TOMOYO Linux Cross Reference
Linux/fs/inode.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    * (C) 1997 Linus Torvalds
    * (C) 1999 Andrea Arcangeli <andrea@suse.de> (dynamic inode allocation)
    */
   #include <linux/export.h>
   #include <linux/fs.h>
   #include <linux/filelock.h>
   #include <linux/mm.h>
  #include <linux/backing-dev.h>
  #include <linux/hash.h>
  #include <linux/swap.h>
  #include <linux/security.h>
  #include <linux/cdev.h>
  #include <linux/memblock.h>
  #include <linux/fsnotify.h>
  #include <linux/mount.h>
  #include <linux/posix_acl.h>
  #include <linux/buffer_head.h> /* for inode_has_buffers */
  #include <linux/ratelimit.h>
  #include <linux/list_lru.h>
  #include <linux/iversion.h>
  #include <linux/rw_hint.h>
  #include <trace/events/writeback.h>
  #include "internal.h"
  
  /*
   * Inode locking rules:
   *
   * inode->i_lock protects:
   *   inode->i_state, inode->i_hash, __iget(), inode->i_io_list
   * Inode LRU list locks protect:
   *   inode->i_sb->s_inode_lru, inode->i_lru
   * inode->i_sb->s_inode_list_lock protects:
   *   inode->i_sb->s_inodes, inode->i_sb_list
   * bdi->wb.list_lock protects:
   *   bdi->wb.b_{dirty,io,more_io,dirty_time}, inode->i_io_list
   * inode_hash_lock protects:
   *   inode_hashtable, inode->i_hash
   *
   * Lock ordering:
   *
   * inode->i_sb->s_inode_list_lock
   *   inode->i_lock
   *     Inode LRU list locks
   *
   * bdi->wb.list_lock
   *   inode->i_lock
   *
   * inode_hash_lock
   *   inode->i_sb->s_inode_list_lock
   *   inode->i_lock
   *
   * iunique_lock
   *   inode_hash_lock
   */
  
  static unsigned int i_hash_mask __ro_after_init;
  static unsigned int i_hash_shift __ro_after_init;
  static struct hlist_head *inode_hashtable __ro_after_init;
  static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);
  
  /*
   * Empty aops. Can be used for the cases where the user does not
   * define any of the address_space operations.
   */
  const struct address_space_operations empty_aops = {
  };
  EXPORT_SYMBOL(empty_aops);
  
  static DEFINE_PER_CPU(unsigned long, nr_inodes);
  static DEFINE_PER_CPU(unsigned long, nr_unused);
  
  static struct kmem_cache *inode_cachep __ro_after_init;
  
  static long get_nr_inodes(void)
  {
          int i;
          long sum = 0;
          for_each_possible_cpu(i)
                  sum += per_cpu(nr_inodes, i);
          return sum < 0 ? 0 : sum;
  }
  
  static inline long get_nr_inodes_unused(void)
  {
          int i;
          long sum = 0;
          for_each_possible_cpu(i)
                  sum += per_cpu(nr_unused, i);
          return sum < 0 ? 0 : sum;
  }
  
  long get_nr_dirty_inodes(void)
  {
          /* not actually dirty inodes, but a wild approximation */
          long nr_dirty = get_nr_inodes() - get_nr_inodes_unused();
          return nr_dirty > 0 ? nr_dirty : 0;
  }
 
 /*
  * Handle nr_inode sysctl
  */
 #ifdef CONFIG_SYSCTL
 /*
  * Statistics gathering..
  */
 static struct inodes_stat_t inodes_stat;
 
 static int proc_nr_inodes(const struct ctl_table *table, int write, void *buffer,
                           size_t *lenp, loff_t *ppos)
 {
         inodes_stat.nr_inodes = get_nr_inodes();
         inodes_stat.nr_unused = get_nr_inodes_unused();
         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
 
 static struct ctl_table inodes_sysctls[] = {
         {
                 .procname       = "inode-nr",
                 .data           = &inodes_stat,
                 .maxlen         = 2*sizeof(long),
                 .mode           = 0444,
                 .proc_handler   = proc_nr_inodes,
         },
         {
                 .procname       = "inode-state",
                 .data           = &inodes_stat,
                 .maxlen         = 7*sizeof(long),
                 .mode           = 0444,
                 .proc_handler   = proc_nr_inodes,
         },
 };
 
 static int __init init_fs_inode_sysctls(void)
 {
         register_sysctl_init("fs", inodes_sysctls);
         return 0;
 }
 early_initcall(init_fs_inode_sysctls);
 #endif
 
 static int no_open(struct inode *inode, struct file *file)
 {
         return -ENXIO;
 }
 
 /**
  * inode_init_always - perform inode structure initialisation
  * @sb: superblock inode belongs to
  * @inode: inode to initialise
  *
  * These are initializations that need to be done on every inode
  * allocation as the fields are not initialised by slab allocation.
  */
 int inode_init_always(struct super_block *sb, struct inode *inode)
 {
         static const struct inode_operations empty_iops;
         static const struct file_operations no_open_fops = {.open = no_open};
         struct address_space *const mapping = &inode->i_data;
 
         inode->i_sb = sb;
         inode->i_blkbits = sb->s_blocksize_bits;
         inode->i_flags = 0;
         inode->i_state = 0;
         atomic64_set(&inode->i_sequence, 0);
         atomic_set(&inode->i_count, 1);
         inode->i_op = &empty_iops;
         inode->i_fop = &no_open_fops;
         inode->i_ino = 0;
         inode->__i_nlink = 1;
         inode->i_opflags = 0;
         if (sb->s_xattr)
                 inode->i_opflags |= IOP_XATTR;
         i_uid_write(inode, 0);
         i_gid_write(inode, 0);
         atomic_set(&inode->i_writecount, 0);
         inode->i_size = 0;
         inode->i_write_hint = WRITE_LIFE_NOT_SET;
         inode->i_blocks = 0;
         inode->i_bytes = 0;
         inode->i_generation = 0;
         inode->i_pipe = NULL;
         inode->i_cdev = NULL;
         inode->i_link = NULL;
         inode->i_dir_seq = 0;
         inode->i_rdev = 0;
         inode->dirtied_when = 0;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
         inode->i_wb_frn_winner = 0;
         inode->i_wb_frn_avg_time = 0;
         inode->i_wb_frn_history = 0;
 #endif
 
         spin_lock_init(&inode->i_lock);
         lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
 
         init_rwsem(&inode->i_rwsem);
         lockdep_set_class(&inode->i_rwsem, &sb->s_type->i_mutex_key);
 
         atomic_set(&inode->i_dio_count, 0);
 
         mapping->a_ops = &empty_aops;
         mapping->host = inode;
         mapping->flags = 0;
         mapping->wb_err = 0;
         atomic_set(&mapping->i_mmap_writable, 0);
 #ifdef CONFIG_READ_ONLY_THP_FOR_FS
         atomic_set(&mapping->nr_thps, 0);
 #endif
         mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
         mapping->i_private_data = NULL;
         mapping->writeback_index = 0;
         init_rwsem(&mapping->invalidate_lock);
         lockdep_set_class_and_name(&mapping->invalidate_lock,
                                    &sb->s_type->invalidate_lock_key,
                                    "mapping.invalidate_lock");
         if (sb->s_iflags & SB_I_STABLE_WRITES)
                 mapping_set_stable_writes(mapping);
         inode->i_private = NULL;
         inode->i_mapping = mapping;
         INIT_HLIST_HEAD(&inode->i_dentry);      /* buggered by rcu freeing */
 #ifdef CONFIG_FS_POSIX_ACL
         inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
 #endif
 
 #ifdef CONFIG_FSNOTIFY
         inode->i_fsnotify_mask = 0;
 #endif
         inode->i_flctx = NULL;
 
         if (unlikely(security_inode_alloc(inode)))
                 return -ENOMEM;
 
         this_cpu_inc(nr_inodes);
 
         return 0;
 }
 EXPORT_SYMBOL(inode_init_always);
 
 void free_inode_nonrcu(struct inode *inode)
 {
         kmem_cache_free(inode_cachep, inode);
 }
 EXPORT_SYMBOL(free_inode_nonrcu);
 
 static void i_callback(struct rcu_head *head)
 {
         struct inode *inode = container_of(head, struct inode, i_rcu);
         if (inode->free_inode)
                 inode->free_inode(inode);
         else
                 free_inode_nonrcu(inode);
 }
 
 static struct inode *alloc_inode(struct super_block *sb)
 {
         const struct super_operations *ops = sb->s_op;
         struct inode *inode;
 
         if (ops->alloc_inode)
                 inode = ops->alloc_inode(sb);
         else
                 inode = alloc_inode_sb(sb, inode_cachep, GFP_KERNEL);
 
         if (!inode)
                 return NULL;
 
         if (unlikely(inode_init_always(sb, inode))) {
                 if (ops->destroy_inode) {
                         ops->destroy_inode(inode);
                         if (!ops->free_inode)
                                 return NULL;
                 }
                 inode->free_inode = ops->free_inode;
                 i_callback(&inode->i_rcu);
                 return NULL;
         }
 
         return inode;
 }
 
 void __destroy_inode(struct inode *inode)
 {
         BUG_ON(inode_has_buffers(inode));
         inode_detach_wb(inode);
         security_inode_free(inode);
         fsnotify_inode_delete(inode);
         locks_free_lock_context(inode);
         if (!inode->i_nlink) {
                 WARN_ON(atomic_long_read(&inode->i_sb->s_remove_count) == 0);
                 atomic_long_dec(&inode->i_sb->s_remove_count);
         }
 
 #ifdef CONFIG_FS_POSIX_ACL
         if (inode->i_acl && !is_uncached_acl(inode->i_acl))
                 posix_acl_release(inode->i_acl);
         if (inode->i_default_acl && !is_uncached_acl(inode->i_default_acl))
                 posix_acl_release(inode->i_default_acl);
 #endif
         this_cpu_dec(nr_inodes);
 }
 EXPORT_SYMBOL(__destroy_inode);
 
 static void destroy_inode(struct inode *inode)
 {
         const struct super_operations *ops = inode->i_sb->s_op;
 
         BUG_ON(!list_empty(&inode->i_lru));
         __destroy_inode(inode);
         if (ops->destroy_inode) {
                 ops->destroy_inode(inode);
                 if (!ops->free_inode)
                         return;
         }
         inode->free_inode = ops->free_inode;
         call_rcu(&inode->i_rcu, i_callback);
 }
 
 /**
  * drop_nlink - directly drop an inode's link count
  * @inode: inode
  *
  * This is a low-level filesystem helper to replace any
  * direct filesystem manipulation of i_nlink.  In cases
  * where we are attempting to track writes to the
  * filesystem, a decrement to zero means an imminent
  * write when the file is truncated and actually unlinked
  * on the filesystem.
  */
 void drop_nlink(struct inode *inode)
 {
         WARN_ON(inode->i_nlink == 0);
         inode->__i_nlink--;
         if (!inode->i_nlink)
                 atomic_long_inc(&inode->i_sb->s_remove_count);
 }
 EXPORT_SYMBOL(drop_nlink);
 
 /**
  * clear_nlink - directly zero an inode's link count
  * @inode: inode
  *
  * This is a low-level filesystem helper to replace any
  * direct filesystem manipulation of i_nlink.  See
  * drop_nlink() for why we care about i_nlink hitting zero.
  */
 void clear_nlink(struct inode *inode)
 {
         if (inode->i_nlink) {
                 inode->__i_nlink = 0;
                 atomic_long_inc(&inode->i_sb->s_remove_count);
         }
 }
 EXPORT_SYMBOL(clear_nlink);
 
 /**
  * set_nlink - directly set an inode's link count
  * @inode: inode
  * @nlink: new nlink (should be non-zero)
  *
  * This is a low-level filesystem helper to replace any
  * direct filesystem manipulation of i_nlink.
  */
 void set_nlink(struct inode *inode, unsigned int nlink)
 {
         if (!nlink) {
                 clear_nlink(inode);
         } else {
                 /* Yes, some filesystems do change nlink from zero to one */
                 if (inode->i_nlink == 0)
                         atomic_long_dec(&inode->i_sb->s_remove_count);
 
                 inode->__i_nlink = nlink;
         }
 }
 EXPORT_SYMBOL(set_nlink);
 
 /**
  * inc_nlink - directly increment an inode's link count
  * @inode: inode
  *
  * This is a low-level filesystem helper to replace any
  * direct filesystem manipulation of i_nlink.  Currently,
  * it is only here for parity with dec_nlink().
  */
 void inc_nlink(struct inode *inode)
 {
         if (unlikely(inode->i_nlink == 0)) {
                 WARN_ON(!(inode->i_state & I_LINKABLE));
                 atomic_long_dec(&inode->i_sb->s_remove_count);
         }
 
         inode->__i_nlink++;
 }
 EXPORT_SYMBOL(inc_nlink);
 
 static void __address_space_init_once(struct address_space *mapping)
 {
         xa_init_flags(&mapping->i_pages, XA_FLAGS_LOCK_IRQ | XA_FLAGS_ACCOUNT);
         init_rwsem(&mapping->i_mmap_rwsem);
         INIT_LIST_HEAD(&mapping->i_private_list);
         spin_lock_init(&mapping->i_private_lock);
         mapping->i_mmap = RB_ROOT_CACHED;
 }
 
 void address_space_init_once(struct address_space *mapping)
 {
         memset(mapping, 0, sizeof(*mapping));
         __address_space_init_once(mapping);
 }
 EXPORT_SYMBOL(address_space_init_once);
 
 /*
  * These are initializations that only need to be done
  * once, because the fields are idempotent across use
  * of the inode, so let the slab aware of that.
  */
 void inode_init_once(struct inode *inode)
 {
         memset(inode, 0, sizeof(*inode));
         INIT_HLIST_NODE(&inode->i_hash);
         INIT_LIST_HEAD(&inode->i_devices);
         INIT_LIST_HEAD(&inode->i_io_list);
         INIT_LIST_HEAD(&inode->i_wb_list);
         INIT_LIST_HEAD(&inode->i_lru);
         INIT_LIST_HEAD(&inode->i_sb_list);
         __address_space_init_once(&inode->i_data);
         i_size_ordered_init(inode);
 }
 EXPORT_SYMBOL(inode_init_once);
 
 static void init_once(void *foo)
 {
         struct inode *inode = (struct inode *) foo;
 
         inode_init_once(inode);
 }
 
 /*
  * inode->i_lock must be held
  */
 void __iget(struct inode *inode)
 {
         atomic_inc(&inode->i_count);
 }
 
 /*
  * get additional reference to inode; caller must already hold one.
  */
 void ihold(struct inode *inode)
 {
         WARN_ON(atomic_inc_return(&inode->i_count) < 2);
 }
 EXPORT_SYMBOL(ihold);
 
 static void __inode_add_lru(struct inode *inode, bool rotate)
 {
         if (inode->i_state & (I_DIRTY_ALL | I_SYNC | I_FREEING | I_WILL_FREE))
                 return;
         if (atomic_read(&inode->i_count))
                 return;
         if (!(inode->i_sb->s_flags & SB_ACTIVE))
                 return;
         if (!mapping_shrinkable(&inode->i_data))
                 return;
 
         if (list_lru_add_obj(&inode->i_sb->s_inode_lru, &inode->i_lru))
                 this_cpu_inc(nr_unused);
         else if (rotate)
                 inode->i_state |= I_REFERENCED;
 }
 
 /*
  * Add inode to LRU if needed (inode is unused and clean).
  *
  * Needs inode->i_lock held.
  */
 void inode_add_lru(struct inode *inode)
 {
         __inode_add_lru(inode, false);
 }
 
 static void inode_lru_list_del(struct inode *inode)
 {
         if (list_lru_del_obj(&inode->i_sb->s_inode_lru, &inode->i_lru))
                 this_cpu_dec(nr_unused);
 }
 
 static void inode_pin_lru_isolating(struct inode *inode)
 {
         lockdep_assert_held(&inode->i_lock);
         WARN_ON(inode->i_state & (I_LRU_ISOLATING | I_FREEING | I_WILL_FREE));
         inode->i_state |= I_LRU_ISOLATING;
 }
 
 static void inode_unpin_lru_isolating(struct inode *inode)
 {
         spin_lock(&inode->i_lock);
         WARN_ON(!(inode->i_state & I_LRU_ISOLATING));
         inode->i_state &= ~I_LRU_ISOLATING;
         smp_mb();
         wake_up_bit(&inode->i_state, __I_LRU_ISOLATING);
         spin_unlock(&inode->i_lock);
 }
 
 static void inode_wait_for_lru_isolating(struct inode *inode)
 {
         spin_lock(&inode->i_lock);
         if (inode->i_state & I_LRU_ISOLATING) {
                 DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LRU_ISOLATING);
                 wait_queue_head_t *wqh;
 
                 wqh = bit_waitqueue(&inode->i_state, __I_LRU_ISOLATING);
                 spin_unlock(&inode->i_lock);
                 __wait_on_bit(wqh, &wq, bit_wait, TASK_UNINTERRUPTIBLE);
                 spin_lock(&inode->i_lock);
                 WARN_ON(inode->i_state & I_LRU_ISOLATING);
         }
         spin_unlock(&inode->i_lock);
 }
 
 /**
  * inode_sb_list_add - add inode to the superblock list of inodes
  * @inode: inode to add
  */
 void inode_sb_list_add(struct inode *inode)
 {
         spin_lock(&inode->i_sb->s_inode_list_lock);
         list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
         spin_unlock(&inode->i_sb->s_inode_list_lock);
 }
 EXPORT_SYMBOL_GPL(inode_sb_list_add);
 
 static inline void inode_sb_list_del(struct inode *inode)
 {
         if (!list_empty(&inode->i_sb_list)) {
                 spin_lock(&inode->i_sb->s_inode_list_lock);
                 list_del_init(&inode->i_sb_list);
                 spin_unlock(&inode->i_sb->s_inode_list_lock);
         }
 }
 
 static unsigned long hash(struct super_block *sb, unsigned long hashval)
 {
         unsigned long tmp;
 
         tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
                         L1_CACHE_BYTES;
         tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> i_hash_shift);
         return tmp & i_hash_mask;
 }
 
 /**
  *      __insert_inode_hash - hash an inode
  *      @inode: unhashed inode
  *      @hashval: unsigned long value used to locate this object in the
  *              inode_hashtable.
  *
  *      Add an inode to the inode hash for this superblock.
  */
 void __insert_inode_hash(struct inode *inode, unsigned long hashval)
 {
         struct hlist_head *b = inode_hashtable + hash(inode->i_sb, hashval);
 
         spin_lock(&inode_hash_lock);
         spin_lock(&inode->i_lock);
         hlist_add_head_rcu(&inode->i_hash, b);
         spin_unlock(&inode->i_lock);
         spin_unlock(&inode_hash_lock);
 }
 EXPORT_SYMBOL(__insert_inode_hash);
 
 /**
  *      __remove_inode_hash - remove an inode from the hash
  *      @inode: inode to unhash
  *
  *      Remove an inode from the superblock.
  */
 void __remove_inode_hash(struct inode *inode)
 {
         spin_lock(&inode_hash_lock);
         spin_lock(&inode->i_lock);
         hlist_del_init_rcu(&inode->i_hash);
         spin_unlock(&inode->i_lock);
         spin_unlock(&inode_hash_lock);
 }
 EXPORT_SYMBOL(__remove_inode_hash);
 
 void dump_mapping(const struct address_space *mapping)
 {
         struct inode *host;
         const struct address_space_operations *a_ops;
         struct hlist_node *dentry_first;
         struct dentry *dentry_ptr;
         struct dentry dentry;
         char fname[64] = {};
         unsigned long ino;
 
         /*
          * If mapping is an invalid pointer, we don't want to crash
          * accessing it, so probe everything depending on it carefully.
          */
         if (get_kernel_nofault(host, &mapping->host) ||
             get_kernel_nofault(a_ops, &mapping->a_ops)) {
                 pr_warn("invalid mapping:%px\n", mapping);
                 return;
         }
 
         if (!host) {
                 pr_warn("aops:%ps\n", a_ops);
                 return;
         }
 
         if (get_kernel_nofault(dentry_first, &host->i_dentry.first) ||
             get_kernel_nofault(ino, &host->i_ino)) {
                 pr_warn("aops:%ps invalid inode:%px\n", a_ops, host);
                 return;
         }
 
         if (!dentry_first) {
                 pr_warn("aops:%ps ino:%lx\n", a_ops, ino);
                 return;
         }
 
         dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
         if (get_kernel_nofault(dentry, dentry_ptr) ||
             !dentry.d_parent || !dentry.d_name.name) {
                 pr_warn("aops:%ps ino:%lx invalid dentry:%px\n",
                                 a_ops, ino, dentry_ptr);
                 return;
         }
 
         if (strncpy_from_kernel_nofault(fname, dentry.d_name.name, 63) < 0)
                 strscpy(fname, "<invalid>");
         /*
          * Even if strncpy_from_kernel_nofault() succeeded,
          * the fname could be unreliable
          */
         pr_warn("aops:%ps ino:%lx dentry name(?):\"%s\"\n",
                 a_ops, ino, fname);
 }
 
 void clear_inode(struct inode *inode)
 {
         /*
          * We have to cycle the i_pages lock here because reclaim can be in the
          * process of removing the last page (in __filemap_remove_folio())
          * and we must not free the mapping under it.
          */
         xa_lock_irq(&inode->i_data.i_pages);
         BUG_ON(inode->i_data.nrpages);
         /*
          * Almost always, mapping_empty(&inode->i_data) here; but there are
          * two known and long-standing ways in which nodes may get left behind
          * (when deep radix-tree node allocation failed partway; or when THP
          * collapse_file() failed). Until those two known cases are cleaned up,
          * or a cleanup function is called here, do not BUG_ON(!mapping_empty),
          * nor even WARN_ON(!mapping_empty).
          */
         xa_unlock_irq(&inode->i_data.i_pages);
         BUG_ON(!list_empty(&inode->i_data.i_private_list));
         BUG_ON(!(inode->i_state & I_FREEING));
         BUG_ON(inode->i_state & I_CLEAR);
         BUG_ON(!list_empty(&inode->i_wb_list));
         /* don't need i_lock here, no concurrent mods to i_state */
         inode->i_state = I_FREEING | I_CLEAR;
 }
 EXPORT_SYMBOL(clear_inode);
 
 /*
  * Free the inode passed in, removing it from the lists it is still connected
  * to. We remove any pages still attached to the inode and wait for any IO that
  * is still in progress before finally destroying the inode.
  *
  * An inode must already be marked I_FREEING so that we avoid the inode being
  * moved back onto lists if we race with other code that manipulates the lists
  * (e.g. writeback_single_inode). The caller is responsible for setting this.
  *
  * An inode must already be removed from the LRU list before being evicted from
  * the cache. This should occur atomically with setting the I_FREEING state
  * flag, so no inodes here should ever be on the LRU when being evicted.
  */
 static void evict(struct inode *inode)
 {
         const struct super_operations *op = inode->i_sb->s_op;
 
         BUG_ON(!(inode->i_state & I_FREEING));
         BUG_ON(!list_empty(&inode->i_lru));
 
         if (!list_empty(&inode->i_io_list))
                 inode_io_list_del(inode);
 
         inode_sb_list_del(inode);
 
         inode_wait_for_lru_isolating(inode);
 
         /*
          * Wait for flusher thread to be done with the inode so that filesystem
          * does not start destroying it while writeback is still running. Since
          * the inode has I_FREEING set, flusher thread won't start new work on
          * the inode.  We just have to wait for running writeback to finish.
          */
         inode_wait_for_writeback(inode);
 
         if (op->evict_inode) {
                 op->evict_inode(inode);
         } else {
                 truncate_inode_pages_final(&inode->i_data);
                 clear_inode(inode);
         }
         if (S_ISCHR(inode->i_mode) && inode->i_cdev)
                 cd_forget(inode);
 
         remove_inode_hash(inode);
 
         /*
          * Wake up waiters in __wait_on_freeing_inode().
          *
          * Lockless hash lookup may end up finding the inode before we removed
          * it above, but only lock it *after* we are done with the wakeup below.
          * In this case the potential waiter cannot safely block.
          *
          * The inode being unhashed after the call to remove_inode_hash() is
          * used as an indicator whether blocking on it is safe.
          */
         spin_lock(&inode->i_lock);
         wake_up_bit(&inode->i_state, __I_NEW);
         BUG_ON(inode->i_state != (I_FREEING | I_CLEAR));
         spin_unlock(&inode->i_lock);
 
         destroy_inode(inode);
 }
 
 /*
  * dispose_list - dispose of the contents of a local list
  * @head: the head of the list to free
  *
  * Dispose-list gets a local list with local inodes in it, so it doesn't
  * need to worry about list corruption and SMP locks.
  */
 static void dispose_list(struct list_head *head)
 {
         while (!list_empty(head)) {
                 struct inode *inode;
 
                 inode = list_first_entry(head, struct inode, i_lru);
                 list_del_init(&inode->i_lru);
 
                 evict(inode);
                 cond_resched();
         }
 }
 
 /**
  * evict_inodes - evict all evictable inodes for a superblock
  * @sb:         superblock to operate on
  *
  * Make sure that no inodes with zero refcount are retained.  This is
  * called by superblock shutdown after having SB_ACTIVE flag removed,
  * so any inode reaching zero refcount during or after that call will
  * be immediately evicted.
  */
 void evict_inodes(struct super_block *sb)
 {
         struct inode *inode, *next;
         LIST_HEAD(dispose);
 
 again:
         spin_lock(&sb->s_inode_list_lock);
         list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                 if (atomic_read(&inode->i_count))
                         continue;
 
                 spin_lock(&inode->i_lock);
                 if (atomic_read(&inode->i_count)) {
                         spin_unlock(&inode->i_lock);
                         continue;
                 }
                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                         spin_unlock(&inode->i_lock);
                         continue;
                 }
 
                 inode->i_state |= I_FREEING;
                 inode_lru_list_del(inode);
                 spin_unlock(&inode->i_lock);
                 list_add(&inode->i_lru, &dispose);
 
                 /*
                  * We can have a ton of inodes to evict at unmount time given
                  * enough memory, check to see if we need to go to sleep for a
                  * bit so we don't livelock.
                  */
                 if (need_resched()) {
                         spin_unlock(&sb->s_inode_list_lock);
                         cond_resched();
                         dispose_list(&dispose);
                         goto again;
                 }
         }
         spin_unlock(&sb->s_inode_list_lock);
 
         dispose_list(&dispose);
 }
 EXPORT_SYMBOL_GPL(evict_inodes);
 
 /**
  * invalidate_inodes    - attempt to free all inodes on a superblock
  * @sb:         superblock to operate on
  *
  * Attempts to free all inodes (including dirty inodes) for a given superblock.
  */
 void invalidate_inodes(struct super_block *sb)
 {
         struct inode *inode, *next;
         LIST_HEAD(dispose);
 
 again:
         spin_lock(&sb->s_inode_list_lock);
         list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                 spin_lock(&inode->i_lock);
                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                         spin_unlock(&inode->i_lock);
                         continue;
                 }
                 if (atomic_read(&inode->i_count)) {
                         spin_unlock(&inode->i_lock);
                         continue;
                 }
 
                 inode->i_state |= I_FREEING;
                 inode_lru_list_del(inode);
                 spin_unlock(&inode->i_lock);
                 list_add(&inode->i_lru, &dispose);
                 if (need_resched()) {
                         spin_unlock(&sb->s_inode_list_lock);
                         cond_resched();
                         dispose_list(&dispose);
                         goto again;
                 }
         }
         spin_unlock(&sb->s_inode_list_lock);
 
         dispose_list(&dispose);
 }
 
 /*
  * Isolate the inode from the LRU in preparation for freeing it.
  *
  * If the inode has the I_REFERENCED flag set, then it means that it has been
  * used recently - the flag is set in iput_final(). When we encounter such an
  * inode, clear the flag and move it to the back of the LRU so it gets another
  * pass through the LRU before it gets reclaimed. This is necessary because of
  * the fact we are doing lazy LRU updates to minimise lock contention so the
  * LRU does not have strict ordering. Hence we don't want to reclaim inodes
  * with this flag set because they are the inodes that are out of order.
  */
 static enum lru_status inode_lru_isolate(struct list_head *item,
                 struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 {
         struct list_head *freeable = arg;
         struct inode    *inode = container_of(item, struct inode, i_lru);
 
         /*
          * We are inverting the lru lock/inode->i_lock here, so use a
          * trylock. If we fail to get the lock, just skip it.
          */
         if (!spin_trylock(&inode->i_lock))
                 return LRU_SKIP;
 
         /*
          * Inodes can get referenced, redirtied, or repopulated while
          * they're already on the LRU, and this can make them
          * unreclaimable for a while. Remove them lazily here; iput,
          * sync, or the last page cache deletion will requeue them.
          */
         if (atomic_read(&inode->i_count) ||
             (inode->i_state & ~I_REFERENCED) ||
             !mapping_shrinkable(&inode->i_data)) {
                 list_lru_isolate(lru, &inode->i_lru);
                 spin_unlock(&inode->i_lock);
                 this_cpu_dec(nr_unused);
                 return LRU_REMOVED;
         }
 
         /* Recently referenced inodes get one more pass */
         if (inode->i_state & I_REFERENCED) {
                 inode->i_state &= ~I_REFERENCED;
                 spin_unlock(&inode->i_lock);
                 return LRU_ROTATE;
         }
 
         /*
          * On highmem systems, mapping_shrinkable() permits dropping
          * page cache in order to free up struct inodes: lowmem might
          * be under pressure before the cache inside the highmem zone.
          */
         if (inode_has_buffers(inode) || !mapping_empty(&inode->i_data)) {
                 inode_pin_lru_isolating(inode);
                 spin_unlock(&inode->i_lock);
                 spin_unlock(lru_lock);
                 if (remove_inode_buffers(inode)) {
                         unsigned long reap;
                         reap = invalidate_mapping_pages(&inode->i_data, 0, -1);
                         if (current_is_kswapd())
                                 __count_vm_events(KSWAPD_INODESTEAL, reap);
                         else
                                 __count_vm_events(PGINODESTEAL, reap);
                         mm_account_reclaimed_pages(reap);
                 }
                 inode_unpin_lru_isolating(inode);
                 spin_lock(lru_lock);
                 return LRU_RETRY;
         }
 
         WARN_ON(inode->i_state & I_NEW);
         inode->i_state |= I_FREEING;
         list_lru_isolate_move(lru, &inode->i_lru, freeable);
         spin_unlock(&inode->i_lock);
 
         this_cpu_dec(nr_unused);
         return LRU_REMOVED;
 }
 
 /*
  * Walk the superblock inode LRU for freeable inodes and attempt to free them.
  * This is called from the superblock shrinker function with a number of inodes
  * to trim from the LRU. Inodes to be freed are moved to a temporary list and
  * then are freed outside inode_lock by dispose_list().
  */
 long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
 {
         LIST_HEAD(freeable);
         long freed;
 
         freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,
                                      inode_lru_isolate, &freeable);
         dispose_list(&freeable);
         return freed;
 }
 
 static void __wait_on_freeing_inode(struct inode *inode, bool is_inode_hash_locked);
 /*
  * Called with the inode lock held.
  */
 static struct inode *find_inode(struct super_block *sb,
                                 struct hlist_head *head,
                                 int (*test)(struct inode *, void *),
                                 void *data, bool is_inode_hash_locked)
 {
         struct inode *inode = NULL;
 
         if (is_inode_hash_locked)
                 lockdep_assert_held(&inode_hash_lock);
         else
                 lockdep_assert_not_held(&inode_hash_lock);
 
         rcu_read_lock();
 repeat:
         hlist_for_each_entry_rcu(inode, head, i_hash) {
                 if (inode->i_sb != sb)
                         continue;
                 if (!test(inode, data))
                         continue;
                 spin_lock(&inode->i_lock);
                 if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                         __wait_on_freeing_inode(inode, is_inode_hash_locked);
                         goto repeat;
                 }
                 if (unlikely(inode->i_state & I_CREATING)) {
                         spin_unlock(&inode->i_lock);
                         rcu_read_unlock();
                         return ERR_PTR(-ESTALE);
                 }
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
                 rcu_read_unlock();
                 return inode;
         }
         rcu_read_unlock();
         return NULL;
 }
 
 /*
  * find_inode_fast is the fast path version of find_inode, see the comment at
  * iget_locked for details.
  */
 static struct inode *find_inode_fast(struct super_block *sb,
                                 struct hlist_head *head, unsigned long ino,
                                 bool is_inode_hash_locked)
 {
         struct inode *inode = NULL;
 
         if (is_inode_hash_locked)
                 lockdep_assert_held(&inode_hash_lock);
         else
                 lockdep_assert_not_held(&inode_hash_lock);
 
         rcu_read_lock();
 repeat:
         hlist_for_each_entry_rcu(inode, head, i_hash) {
                 if (inode->i_ino != ino)
                         continue;
                 if (inode->i_sb != sb)
                         continue;
                 spin_lock(&inode->i_lock);
                 if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                         __wait_on_freeing_inode(inode, is_inode_hash_locked);
                         goto repeat;
                 }
                 if (unlikely(inode->i_state & I_CREATING)) {
                         spin_unlock(&inode->i_lock);
                         rcu_read_unlock();
                         return ERR_PTR(-ESTALE);
                 }
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
                 rcu_read_unlock();
                 return inode;
         }
         rcu_read_unlock();
         return NULL;
 }
 
 /*
  * Each cpu owns a range of LAST_INO_BATCH numbers.
  * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations,
  * to renew the exhausted range.
  *
  * This does not significantly increase overflow rate because every CPU can
  * consume at most LAST_INO_BATCH-1 unused inode numbers. So there is
  * NR_CPUS*(LAST_INO_BATCH-1) wastage. At 4096 and 1024, this is ~0.1% of the
  * 2^32 range, and is a worst-case. Even a 50% wastage would only increase
  * overflow rate by 2x, which does not seem too significant.
  *
  * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
  * error if st_ino won't fit in target struct field. Use 32bit counter
  * here to attempt to avoid that.
  */
 #define LAST_INO_BATCH 1024
 static DEFINE_PER_CPU(unsigned int, last_ino);
 
 unsigned int get_next_ino(void)
 {
         unsigned int *p = &get_cpu_var(last_ino);
         unsigned int res = *p;
 
 #ifdef CONFIG_SMP
         if (unlikely((res & (LAST_INO_BATCH-1)) == 0)) {
                 static atomic_t shared_last_ino;
                 int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino);
 
                 res = next - LAST_INO_BATCH;
         }
 #endif
 
         res++;
         /* get_next_ino should not provide a 0 inode number */
         if (unlikely(!res))
                 res++;
         *p = res;
         put_cpu_var(last_ino);
         return res;
 }
 EXPORT_SYMBOL(get_next_ino);
 
 /**
  *      new_inode_pseudo        - obtain an inode
  *      @sb: superblock
  *
  *      Allocates a new inode for given superblock.
  *      Inode wont be chained in superblock s_inodes list
  *      This means :
  *      - fs can't be unmount
  *      - quotas, fsnotify, writeback can't work
  */
 struct inode *new_inode_pseudo(struct super_block *sb)
 {
         return alloc_inode(sb);
 }
 
 /**
  *      new_inode       - obtain an inode
  *      @sb: superblock
  *
  *      Allocates a new inode for given superblock. The default gfp_mask
  *      for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE.
  *      If HIGHMEM pages are unsuitable or it is known that pages allocated
  *      for the page cache are not reclaimable or migratable,
  *      mapping_set_gfp_mask() must be called with suitable flags on the
  *      newly created inode's mapping
  *
  */
 struct inode *new_inode(struct super_block *sb)
 {
         struct inode *inode;
 
         inode = new_inode_pseudo(sb);
         if (inode)
                 inode_sb_list_add(inode);
         return inode;
 }
 EXPORT_SYMBOL(new_inode);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void lockdep_annotate_inode_mutex_key(struct inode *inode)
 {
         if (S_ISDIR(inode->i_mode)) {
                 struct file_system_type *type = inode->i_sb->s_type;
 
                 /* Set new key only if filesystem hasn't already changed it */
                 if (lockdep_match_class(&inode->i_rwsem, &type->i_mutex_key)) {
                         /*
                          * ensure nobody is actually holding i_mutex
                          */
                         // mutex_destroy(&inode->i_mutex);
                         init_rwsem(&inode->i_rwsem);
                         lockdep_set_class(&inode->i_rwsem,
                                           &type->i_mutex_dir_key);
                 }
         }
 }
 EXPORT_SYMBOL(lockdep_annotate_inode_mutex_key);
 #endif
 
 /**
  * unlock_new_inode - clear the I_NEW state and wake up any waiters
  * @inode:      new inode to unlock
  *
  * Called when the inode is fully initialised to clear the new state of the
  * inode and wake up anyone waiting for the inode to finish initialisation.
  */
 void unlock_new_inode(struct inode *inode)
 {
         lockdep_annotate_inode_mutex_key(inode);
         spin_lock(&inode->i_lock);
         WARN_ON(!(inode->i_state & I_NEW));
         inode->i_state &= ~I_NEW & ~I_CREATING;
         smp_mb();
         wake_up_bit(&inode->i_state, __I_NEW);
         spin_unlock(&inode->i_lock);
 }
 EXPORT_SYMBOL(unlock_new_inode);
 
 void discard_new_inode(struct inode *inode)
 {
         lockdep_annotate_inode_mutex_key(inode);
         spin_lock(&inode->i_lock);
         WARN_ON(!(inode->i_state & I_NEW));
         inode->i_state &= ~I_NEW;
         smp_mb();
         wake_up_bit(&inode->i_state, __I_NEW);
         spin_unlock(&inode->i_lock);
         iput(inode);
 }
 EXPORT_SYMBOL(discard_new_inode);
 
 /**
  * lock_two_nondirectories - take two i_mutexes on non-directory objects
  *
  * Lock any non-NULL argument. Passed objects must not be directories.
  * Zero, one or two objects may be locked by this function.
  *
  * @inode1: first inode to lock
  * @inode2: second inode to lock
  */
 void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
 {
         if (inode1)
                 WARN_ON_ONCE(S_ISDIR(inode1->i_mode));
         if (inode2)
                 WARN_ON_ONCE(S_ISDIR(inode2->i_mode));
         if (inode1 > inode2)
                 swap(inode1, inode2);
         if (inode1)
                 inode_lock(inode1);
         if (inode2 && inode2 != inode1)
                 inode_lock_nested(inode2, I_MUTEX_NONDIR2);
 }
 EXPORT_SYMBOL(lock_two_nondirectories);
 
 /**
  * unlock_two_nondirectories - release locks from lock_two_nondirectories()
  * @inode1: first inode to unlock
  * @inode2: second inode to unlock
  */
 void unlock_two_nondirectories(struct inode *inode1, struct inode *inode2)
 {
         if (inode1) {
                 WARN_ON_ONCE(S_ISDIR(inode1->i_mode));
                 inode_unlock(inode1);
         }
         if (inode2 && inode2 != inode1) {
                 WARN_ON_ONCE(S_ISDIR(inode2->i_mode));
                 inode_unlock(inode2);
         }
 }
 EXPORT_SYMBOL(unlock_two_nondirectories);
 
 /**
  * inode_insert5 - obtain an inode from a mounted file system
  * @inode:      pre-allocated inode to use for insert to cache
  * @hashval:    hash value (usually inode number) to get
  * @test:       callback used for comparisons between inodes
  * @set:        callback used to initialize a new struct inode
  * @data:       opaque data pointer to pass to @test and @set
  *
  * Search for the inode specified by @hashval and @data in the inode cache,
  * and if present it is return it with an increased reference count. This is
  * a variant of iget5_locked() for callers that don't want to fail on memory
  * allocation of inode.
  *
  * If the inode is not in cache, insert the pre-allocated inode to cache and
  * return it locked, hashed, and with the I_NEW flag set. The file system gets
  * to fill it in before unlocking it via unlock_new_inode().
  *
  * Note both @test and @set are called with the inode_hash_lock held, so can't
  * sleep.
  */
 struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
                             int (*test)(struct inode *, void *),
                             int (*set)(struct inode *, void *), void *data)
 {
         struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
         struct inode *old;
 
 again:
         spin_lock(&inode_hash_lock);
         old = find_inode(inode->i_sb, head, test, data, true);
         if (unlikely(old)) {
                 /*
                  * Uhhuh, somebody else created the same inode under us.
                  * Use the old inode instead of the preallocated one.
                  */
                 spin_unlock(&inode_hash_lock);
                 if (IS_ERR(old))
                         return NULL;
                 wait_on_inode(old);
                 if (unlikely(inode_unhashed(old))) {
                         iput(old);
                         goto again;
                 }
                 return old;
         }
 
         if (set && unlikely(set(inode, data))) {
                 inode = NULL;
                 goto unlock;
         }
 
         /*
          * Return the locked inode with I_NEW set, the
          * caller is responsible for filling in the contents
          */
         spin_lock(&inode->i_lock);
         inode->i_state |= I_NEW;
         hlist_add_head_rcu(&inode->i_hash, head);
         spin_unlock(&inode->i_lock);
 
         /*
          * Add inode to the sb list if it's not already. It has I_NEW at this
          * point, so it should be safe to test i_sb_list locklessly.
          */
         if (list_empty(&inode->i_sb_list))
                 inode_sb_list_add(inode);
 unlock:
         spin_unlock(&inode_hash_lock);
 
         return inode;
 }
 EXPORT_SYMBOL(inode_insert5);
 
 /**
  * iget5_locked - obtain an inode from a mounted file system
  * @sb:         super block of file system
  * @hashval:    hash value (usually inode number) to get
  * @test:       callback used for comparisons between inodes
  * @set:        callback used to initialize a new struct inode
  * @data:       opaque data pointer to pass to @test and @set
  *
  * Search for the inode specified by @hashval and @data in the inode cache,
  * and if present it is return it with an increased reference count. This is
  * a generalized version of iget_locked() for file systems where the inode
  * number is not sufficient for unique identification of an inode.
  *
  * If the inode is not in cache, allocate a new inode and return it locked,
  * hashed, and with the I_NEW flag set. The file system gets to fill it in
  * before unlocking it via unlock_new_inode().
  *
  * Note both @test and @set are called with the inode_hash_lock held, so can't
  * sleep.
  */
 struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
                 int (*test)(struct inode *, void *),
                 int (*set)(struct inode *, void *), void *data)
 {
         struct inode *inode = ilookup5(sb, hashval, test, data);
 
         if (!inode) {
                 struct inode *new = alloc_inode(sb);
 
                 if (new) {
                         inode = inode_insert5(new, hashval, test, set, data);
                         if (unlikely(inode != new))
                                 destroy_inode(new);
                 }
         }
         return inode;
 }
 EXPORT_SYMBOL(iget5_locked);
 
 /**
  * iget5_locked_rcu - obtain an inode from a mounted file system
  * @sb:         super block of file system
  * @hashval:    hash value (usually inode number) to get
  * @test:       callback used for comparisons between inodes
  * @set:        callback used to initialize a new struct inode
  * @data:       opaque data pointer to pass to @test and @set
  *
  * This is equivalent to iget5_locked, except the @test callback must
  * tolerate the inode not being stable, including being mid-teardown.
  */
 struct inode *iget5_locked_rcu(struct super_block *sb, unsigned long hashval,
                 int (*test)(struct inode *, void *),
                 int (*set)(struct inode *, void *), void *data)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, hashval);
         struct inode *inode, *new;
 
 again:
         inode = find_inode(sb, head, test, data, false);
         if (inode) {
                 if (IS_ERR(inode))
                         return NULL;
                 wait_on_inode(inode);
                 if (unlikely(inode_unhashed(inode))) {
                         iput(inode);
                         goto again;
                 }
                 return inode;
         }
 
         new = alloc_inode(sb);
         if (new) {
                 inode = inode_insert5(new, hashval, test, set, data);
                 if (unlikely(inode != new))
                         destroy_inode(new);
         }
         return inode;
 }
 EXPORT_SYMBOL_GPL(iget5_locked_rcu);
 
 /**
  * iget_locked - obtain an inode from a mounted file system
  * @sb:         super block of file system
  * @ino:        inode number to get
  *
  * Search for the inode specified by @ino in the inode cache and if present
  * return it with an increased reference count. This is for file systems
  * where the inode number is sufficient for unique identification of an inode.
  *
  * If the inode is not in cache, allocate a new inode and return it locked,
  * hashed, and with the I_NEW flag set.  The file system gets to fill it in
  * before unlocking it via unlock_new_inode().
  */
 struct inode *iget_locked(struct super_block *sb, unsigned long ino)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, ino);
         struct inode *inode;
 again:
         inode = find_inode_fast(sb, head, ino, false);
         if (inode) {
                 if (IS_ERR(inode))
                         return NULL;
                 wait_on_inode(inode);
                 if (unlikely(inode_unhashed(inode))) {
                         iput(inode);
                         goto again;
                 }
                 return inode;
         }
 
         inode = alloc_inode(sb);
         if (inode) {
                 struct inode *old;
 
                 spin_lock(&inode_hash_lock);
                 /* We released the lock, so.. */
                 old = find_inode_fast(sb, head, ino, true);
                 if (!old) {
                         inode->i_ino = ino;
                         spin_lock(&inode->i_lock);
                         inode->i_state = I_NEW;
                         hlist_add_head_rcu(&inode->i_hash, head);
                         spin_unlock(&inode->i_lock);
                         inode_sb_list_add(inode);
                         spin_unlock(&inode_hash_lock);
 
                         /* Return the locked inode with I_NEW set, the
                          * caller is responsible for filling in the contents
                          */
                         return inode;
                 }
 
                 /*
                  * Uhhuh, somebody else created the same inode under
                  * us. Use the old inode instead of the one we just
                  * allocated.
                  */
                 spin_unlock(&inode_hash_lock);
                 destroy_inode(inode);
                 if (IS_ERR(old))
                         return NULL;
                 inode = old;
                 wait_on_inode(inode);
                 if (unlikely(inode_unhashed(inode))) {
                         iput(inode);
                         goto again;
                 }
         }
         return inode;
 }
 EXPORT_SYMBOL(iget_locked);
 
 /*
  * search the inode cache for a matching inode number.
  * If we find one, then the inode number we are trying to
  * allocate is not unique and so we should not use it.
  *
  * Returns 1 if the inode number is unique, 0 if it is not.
  */
 static int test_inode_iunique(struct super_block *sb, unsigned long ino)
 {
         struct hlist_head *b = inode_hashtable + hash(sb, ino);
         struct inode *inode;
 
         hlist_for_each_entry_rcu(inode, b, i_hash) {
                 if (inode->i_ino == ino && inode->i_sb == sb)
                         return 0;
         }
         return 1;
 }
 
 /**
  *      iunique - get a unique inode number
  *      @sb: superblock
  *      @max_reserved: highest reserved inode number
  *
  *      Obtain an inode number that is unique on the system for a given
  *      superblock. This is used by file systems that have no natural
  *      permanent inode numbering system. An inode number is returned that
  *      is higher than the reserved limit but unique.
  *
  *      BUGS:
  *      With a large number of inodes live on the file system this function
  *      currently becomes quite slow.
  */
 ino_t iunique(struct super_block *sb, ino_t max_reserved)
 {
         /*
          * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
          * error if st_ino won't fit in target struct field. Use 32bit counter
          * here to attempt to avoid that.
          */
         static DEFINE_SPINLOCK(iunique_lock);
         static unsigned int counter;
         ino_t res;
 
         rcu_read_lock();
         spin_lock(&iunique_lock);
         do {
                 if (counter <= max_reserved)
                         counter = max_reserved + 1;
                 res = counter++;
         } while (!test_inode_iunique(sb, res));
         spin_unlock(&iunique_lock);
         rcu_read_unlock();
 
         return res;
 }
 EXPORT_SYMBOL(iunique);
 
 struct inode *igrab(struct inode *inode)
 {
         spin_lock(&inode->i_lock);
         if (!(inode->i_state & (I_FREEING|I_WILL_FREE))) {
                 __iget(inode);
                 spin_unlock(&inode->i_lock);
         } else {
                 spin_unlock(&inode->i_lock);
                 /*
                  * Handle the case where s_op->clear_inode is not been
                  * called yet, and somebody is calling igrab
                  * while the inode is getting freed.
                  */
                 inode = NULL;
         }
         return inode;
 }
 EXPORT_SYMBOL(igrab);
 
 /**
  * ilookup5_nowait - search for an inode in the inode cache
  * @sb:         super block of file system to search
  * @hashval:    hash value (usually inode number) to search for
  * @test:       callback used for comparisons between inodes
  * @data:       opaque data pointer to pass to @test
  *
  * Search for the inode specified by @hashval and @data in the inode cache.
  * If the inode is in the cache, the inode is returned with an incremented
  * reference count.
  *
  * Note: I_NEW is not waited upon so you have to be very careful what you do
  * with the returned inode.  You probably should be using ilookup5() instead.
  *
  * Note2: @test is called with the inode_hash_lock held, so can't sleep.
  */
 struct inode *ilookup5_nowait(struct super_block *sb, unsigned long hashval,
                 int (*test)(struct inode *, void *), void *data)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, hashval);
         struct inode *inode;
 
         spin_lock(&inode_hash_lock);
         inode = find_inode(sb, head, test, data, true);
         spin_unlock(&inode_hash_lock);
 
         return IS_ERR(inode) ? NULL : inode;
 }
 EXPORT_SYMBOL(ilookup5_nowait);
 
 /**
  * ilookup5 - search for an inode in the inode cache
  * @sb:         super block of file system to search
  * @hashval:    hash value (usually inode number) to search for
  * @test:       callback used for comparisons between inodes
  * @data:       opaque data pointer to pass to @test
  *
  * Search for the inode specified by @hashval and @data in the inode cache,
  * and if the inode is in the cache, return the inode with an incremented
  * reference count.  Waits on I_NEW before returning the inode.
  * returned with an incremented reference count.
  *
  * This is a generalized version of ilookup() for file systems where the
  * inode number is not sufficient for unique identification of an inode.
  *
  * Note: @test is called with the inode_hash_lock held, so can't sleep.
  */
 struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
                 int (*test)(struct inode *, void *), void *data)
 {
         struct inode *inode;
 again:
         inode = ilookup5_nowait(sb, hashval, test, data);
         if (inode) {
                 wait_on_inode(inode);
                 if (unlikely(inode_unhashed(inode))) {
                         iput(inode);
                         goto again;
                 }
         }
         return inode;
 }
 EXPORT_SYMBOL(ilookup5);
 
 /**
  * ilookup - search for an inode in the inode cache
  * @sb:         super block of file system to search
  * @ino:        inode number to search for
  *
  * Search for the inode @ino in the inode cache, and if the inode is in the
  * cache, the inode is returned with an incremented reference count.
  */
 struct inode *ilookup(struct super_block *sb, unsigned long ino)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, ino);
         struct inode *inode;
 again:
         inode = find_inode_fast(sb, head, ino, false);
 
         if (inode) {
                 if (IS_ERR(inode))
                         return NULL;
                 wait_on_inode(inode);
                 if (unlikely(inode_unhashed(inode))) {
                         iput(inode);
                         goto again;
                 }
         }
         return inode;
 }
 EXPORT_SYMBOL(ilookup);
 
 /**
  * find_inode_nowait - find an inode in the inode cache
  * @sb:         super block of file system to search
  * @hashval:    hash value (usually inode number) to search for
  * @match:      callback used for comparisons between inodes
  * @data:       opaque data pointer to pass to @match
  *
  * Search for the inode specified by @hashval and @data in the inode
  * cache, where the helper function @match will return 0 if the inode
  * does not match, 1 if the inode does match, and -1 if the search
  * should be stopped.  The @match function must be responsible for
  * taking the i_lock spin_lock and checking i_state for an inode being
  * freed or being initialized, and incrementing the reference count
  * before returning 1.  It also must not sleep, since it is called with
  * the inode_hash_lock spinlock held.
  *
  * This is a even more generalized version of ilookup5() when the
  * function must never block --- find_inode() can block in
  * __wait_on_freeing_inode() --- or when the caller can not increment
  * the reference count because the resulting iput() might cause an
  * inode eviction.  The tradeoff is that the @match funtion must be
  * very carefully implemented.
  */
 struct inode *find_inode_nowait(struct super_block *sb,
                                 unsigned long hashval,
                                 int (*match)(struct inode *, unsigned long,
                                              void *),
                                 void *data)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, hashval);
         struct inode *inode, *ret_inode = NULL;
         int mval;
 
         spin_lock(&inode_hash_lock);
         hlist_for_each_entry(inode, head, i_hash) {
                 if (inode->i_sb != sb)
                         continue;
                 mval = match(inode, hashval, data);
                 if (mval == 0)
                         continue;
                 if (mval == 1)
                         ret_inode = inode;
                 goto out;
         }
 out:
         spin_unlock(&inode_hash_lock);
         return ret_inode;
 }
 EXPORT_SYMBOL(find_inode_nowait);
 
 /**
  * find_inode_rcu - find an inode in the inode cache
  * @sb:         Super block of file system to search
  * @hashval:    Key to hash
  * @test:       Function to test match on an inode
  * @data:       Data for test function
  *
  * Search for the inode specified by @hashval and @data in the inode cache,
  * where the helper function @test will return 0 if the inode does not match
  * and 1 if it does.  The @test function must be responsible for taking the
  * i_lock spin_lock and checking i_state for an inode being freed or being
  * initialized.
  *
  * If successful, this will return the inode for which the @test function
  * returned 1 and NULL otherwise.
  *
  * The @test function is not permitted to take a ref on any inode presented.
  * It is also not permitted to sleep.
  *
  * The caller must hold the RCU read lock.
  */
 struct inode *find_inode_rcu(struct super_block *sb, unsigned long hashval,
                              int (*test)(struct inode *, void *), void *data)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, hashval);
         struct inode *inode;
 
         RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
                          "suspicious find_inode_rcu() usage");
 
         hlist_for_each_entry_rcu(inode, head, i_hash) {
                 if (inode->i_sb == sb &&
                     !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)) &&
                     test(inode, data))
                         return inode;
         }
         return NULL;
 }
 EXPORT_SYMBOL(find_inode_rcu);
 
 /**
  * find_inode_by_ino_rcu - Find an inode in the inode cache
  * @sb:         Super block of file system to search
  * @ino:        The inode number to match
  *
  * Search for the inode specified by @hashval and @data in the inode cache,
  * where the helper function @test will return 0 if the inode does not match
  * and 1 if it does.  The @test function must be responsible for taking the
  * i_lock spin_lock and checking i_state for an inode being freed or being
  * initialized.
  *
  * If successful, this will return the inode for which the @test function
  * returned 1 and NULL otherwise.
  *
  * The @test function is not permitted to take a ref on any inode presented.
  * It is also not permitted to sleep.
  *
  * The caller must hold the RCU read lock.
  */
 struct inode *find_inode_by_ino_rcu(struct super_block *sb,
                                     unsigned long ino)
 {
         struct hlist_head *head = inode_hashtable + hash(sb, ino);
         struct inode *inode;
 
         RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
                          "suspicious find_inode_by_ino_rcu() usage");
 
         hlist_for_each_entry_rcu(inode, head, i_hash) {
                 if (inode->i_ino == ino &&
                     inode->i_sb == sb &&
                     !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)))
                     return inode;
         }
         return NULL;
 }
 EXPORT_SYMBOL(find_inode_by_ino_rcu);
 
 int insert_inode_locked(struct inode *inode)
 {
         struct super_block *sb = inode->i_sb;
         ino_t ino = inode->i_ino;
         struct hlist_head *head = inode_hashtable + hash(sb, ino);
 
         while (1) {
                 struct inode *old = NULL;
                 spin_lock(&inode_hash_lock);
                 hlist_for_each_entry(old, head, i_hash) {
                         if (old->i_ino != ino)
                                 continue;
                         if (old->i_sb != sb)
                                 continue;
                         spin_lock(&old->i_lock);
                         if (old->i_state & (I_FREEING|I_WILL_FREE)) {
                                 spin_unlock(&old->i_lock);
                                 continue;
                         }
                         break;
                 }
                 if (likely(!old)) {
                         spin_lock(&inode->i_lock);
                         inode->i_state |= I_NEW | I_CREATING;
                         hlist_add_head_rcu(&inode->i_hash, head);
                         spin_unlock(&inode->i_lock);
                         spin_unlock(&inode_hash_lock);
                         return 0;
                 }
                 if (unlikely(old->i_state & I_CREATING)) {
                         spin_unlock(&old->i_lock);
                         spin_unlock(&inode_hash_lock);
                         return -EBUSY;
                 }
                 __iget(old);
                 spin_unlock(&old->i_lock);
                 spin_unlock(&inode_hash_lock);
                 wait_on_inode(old);
                 if (unlikely(!inode_unhashed(old))) {
                         iput(old);
                         return -EBUSY;
                 }
                 iput(old);
         }
 }
 EXPORT_SYMBOL(insert_inode_locked);
 
 int insert_inode_locked4(struct inode *inode, unsigned long hashval,
                 int (*test)(struct inode *, void *), void *data)
 {
         struct inode *old;
 
         inode->i_state |= I_CREATING;
         old = inode_insert5(inode, hashval, test, NULL, data);
 
         if (old != inode) {
                 iput(old);
                 return -EBUSY;
         }
         return 0;
 }
 EXPORT_SYMBOL(insert_inode_locked4);
 
 
 int generic_delete_inode(struct inode *inode)
 {
         return 1;
 }
 EXPORT_SYMBOL(generic_delete_inode);
 
 /*
  * Called when we're dropping the last reference
  * to an inode.
  *
  * Call the FS "drop_inode()" function, defaulting to
  * the legacy UNIX filesystem behaviour.  If it tells
  * us to evict inode, do so.  Otherwise, retain inode
  * in cache if fs is alive, sync and evict if fs is
  * shutting down.
  */
 static void iput_final(struct inode *inode)
 {
         struct super_block *sb = inode->i_sb;
         const struct super_operations *op = inode->i_sb->s_op;
         unsigned long state;
         int drop;
 
         WARN_ON(inode->i_state & I_NEW);
 
         if (op->drop_inode)
                 drop = op->drop_inode(inode);
         else
                 drop = generic_drop_inode(inode);
 
         if (!drop &&
             !(inode->i_state & I_DONTCACHE) &&
             (sb->s_flags & SB_ACTIVE)) {
                 __inode_add_lru(inode, true);
                 spin_unlock(&inode->i_lock);
                 return;
         }
 
         state = inode->i_state;
         if (!drop) {
                 WRITE_ONCE(inode->i_state, state | I_WILL_FREE);
                 spin_unlock(&inode->i_lock);
 
                 write_inode_now(inode, 1);
 
                 spin_lock(&inode->i_lock);
                 state = inode->i_state;
                 WARN_ON(state & I_NEW);
                 state &= ~I_WILL_FREE;
         }
 
         WRITE_ONCE(inode->i_state, state | I_FREEING);
         if (!list_empty(&inode->i_lru))
                 inode_lru_list_del(inode);
         spin_unlock(&inode->i_lock);
 
         evict(inode);
 }
 
 /**
  *      iput    - put an inode
  *      @inode: inode to put
  *
  *      Puts an inode, dropping its usage count. If the inode use count hits
  *      zero, the inode is then freed and may also be destroyed.
  *
  *      Consequently, iput() can sleep.
  */
 void iput(struct inode *inode)
 {
         if (!inode)
                 return;
         BUG_ON(inode->i_state & I_CLEAR);
 retry:
         if (atomic_dec_and_lock(&inode->i_count, &inode->i_lock)) {
                 if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) {
                         atomic_inc(&inode->i_count);
                         spin_unlock(&inode->i_lock);
                         trace_writeback_lazytime_iput(inode);
                         mark_inode_dirty_sync(inode);
                         goto retry;
                 }
                 iput_final(inode);
         }
 }
 EXPORT_SYMBOL(iput);
 
 #ifdef CONFIG_BLOCK
 /**
  *      bmap    - find a block number in a file
  *      @inode:  inode owning the block number being requested
  *      @block: pointer containing the block to find
  *
  *      Replaces the value in ``*block`` with the block number on the device holding
  *      corresponding to the requested block number in the file.
  *      That is, asked for block 4 of inode 1 the function will replace the
  *      4 in ``*block``, with disk block relative to the disk start that holds that
  *      block of the file.
  *
  *      Returns -EINVAL in case of error, 0 otherwise. If mapping falls into a
  *      hole, returns 0 and ``*block`` is also set to 0.
  */
 int bmap(struct inode *inode, sector_t *block)
 {
         if (!inode->i_mapping->a_ops->bmap)
                 return -EINVAL;
 
         *block = inode->i_mapping->a_ops->bmap(inode->i_mapping, *block);
         return 0;
 }
 EXPORT_SYMBOL(bmap);
 #endif
 
 /*
  * With relative atime, only update atime if the previous atime is
  * earlier than or equal to either the ctime or mtime,
  * or if at least a day has passed since the last atime update.
  */
 static bool relatime_need_update(struct vfsmount *mnt, struct inode *inode,
                              struct timespec64 now)
 {
         struct timespec64 atime, mtime, ctime;
 
         if (!(mnt->mnt_flags & MNT_RELATIME))
                 return true;
         /*
          * Is mtime younger than or equal to atime? If yes, update atime:
          */
         atime = inode_get_atime(inode);
         mtime = inode_get_mtime(inode);
         if (timespec64_compare(&mtime, &atime) >= 0)
                 return true;
         /*
          * Is ctime younger than or equal to atime? If yes, update atime:
          */
         ctime = inode_get_ctime(inode);
         if (timespec64_compare(&ctime, &atime) >= 0)
                 return true;
 
         /*
          * Is the previous atime value older than a day? If yes,
          * update atime:
          */
         if ((long)(now.tv_sec - atime.tv_sec) >= 24*60*60)
                 return true;
         /*
          * Good, we can skip the atime update:
          */
         return false;
 }
 
 /**
  * inode_update_timestamps - update the timestamps on the inode
  * @inode: inode to be updated
  * @flags: S_* flags that needed to be updated
  *
  * The update_time function is called when an inode's timestamps need to be
  * updated for a read or write operation. This function handles updating the
  * actual timestamps. It's up to the caller to ensure that the inode is marked
  * dirty appropriately.
  *
  * In the case where any of S_MTIME, S_CTIME, or S_VERSION need to be updated,
  * attempt to update all three of them. S_ATIME updates can be handled
  * independently of the rest.
  *
  * Returns a set of S_* flags indicating which values changed.
  */
 int inode_update_timestamps(struct inode *inode, int flags)
 {
         int updated = 0;
         struct timespec64 now;
 
         if (flags & (S_MTIME|S_CTIME|S_VERSION)) {
                 struct timespec64 ctime = inode_get_ctime(inode);
                 struct timespec64 mtime = inode_get_mtime(inode);
 
                 now = inode_set_ctime_current(inode);
                 if (!timespec64_equal(&now, &ctime))
                         updated |= S_CTIME;
                 if (!timespec64_equal(&now, &mtime)) {
                         inode_set_mtime_to_ts(inode, now);
                         updated |= S_MTIME;
                 }
                 if (IS_I_VERSION(inode) && inode_maybe_inc_iversion(inode, updated))
                         updated |= S_VERSION;
         } else {
                 now = current_time(inode);
         }
 
         if (flags & S_ATIME) {
                 struct timespec64 atime = inode_get_atime(inode);
 
                 if (!timespec64_equal(&now, &atime)) {
                         inode_set_atime_to_ts(inode, now);
                         updated |= S_ATIME;
                 }
         }
         return updated;
 }
 EXPORT_SYMBOL(inode_update_timestamps);
 
 /**
  * generic_update_time - update the timestamps on the inode
  * @inode: inode to be updated
  * @flags: S_* flags that needed to be updated
  *
  * The update_time function is called when an inode's timestamps need to be
  * updated for a read or write operation. In the case where any of S_MTIME, S_CTIME,
  * or S_VERSION need to be updated we attempt to update all three of them. S_ATIME
  * updates can be handled done independently of the rest.
  *
  * Returns a S_* mask indicating which fields were updated.
  */
 int generic_update_time(struct inode *inode, int flags)
 {
         int updated = inode_update_timestamps(inode, flags);
         int dirty_flags = 0;
 
         if (updated & (S_ATIME|S_MTIME|S_CTIME))
                 dirty_flags = inode->i_sb->s_flags & SB_LAZYTIME ? I_DIRTY_TIME : I_DIRTY_SYNC;
         if (updated & S_VERSION)
                 dirty_flags |= I_DIRTY_SYNC;
         __mark_inode_dirty(inode, dirty_flags);
         return updated;
 }
 EXPORT_SYMBOL(generic_update_time);
 
 /*
  * This does the actual work of updating an inodes time or version.  Must have
  * had called mnt_want_write() before calling this.
  */
 int inode_update_time(struct inode *inode, int flags)
 {
         if (inode->i_op->update_time)
                 return inode->i_op->update_time(inode, flags);
         generic_update_time(inode, flags);
         return 0;
 }
 EXPORT_SYMBOL(inode_update_time);
 
 /**
  *      atime_needs_update      -       update the access time
  *      @path: the &struct path to update
  *      @inode: inode to update
  *
  *      Update the accessed time on an inode and mark it for writeback.
  *      This function automatically handles read only file systems and media,
  *      as well as the "noatime" flag and inode specific "noatime" markers.
  */
 bool atime_needs_update(const struct path *path, struct inode *inode)
 {
         struct vfsmount *mnt = path->mnt;
         struct timespec64 now, atime;
 
         if (inode->i_flags & S_NOATIME)
                 return false;
 
         /* Atime updates will likely cause i_uid and i_gid to be written
          * back improprely if their true value is unknown to the vfs.
          */
         if (HAS_UNMAPPED_ID(mnt_idmap(mnt), inode))
                 return false;
 
         if (IS_NOATIME(inode))
                 return false;
         if ((inode->i_sb->s_flags & SB_NODIRATIME) && S_ISDIR(inode->i_mode))
                 return false;
 
         if (mnt->mnt_flags & MNT_NOATIME)
                 return false;
         if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
                 return false;
 
         now = current_time(inode);
 
         if (!relatime_need_update(mnt, inode, now))
                 return false;
 
         atime = inode_get_atime(inode);
         if (timespec64_equal(&atime, &now))
                 return false;
 
         return true;
 }
 
 void touch_atime(const struct path *path)
 {
         struct vfsmount *mnt = path->mnt;
         struct inode *inode = d_inode(path->dentry);
 
         if (!atime_needs_update(path, inode))
                 return;
 
         if (!sb_start_write_trylock(inode->i_sb))
                 return;
 
         if (mnt_get_write_access(mnt) != 0)
                 goto skip_update;
         /*
          * File systems can error out when updating inodes if they need to
          * allocate new space to modify an inode (such is the case for
          * Btrfs), but since we touch atime while walking down the path we
          * really don't care if we failed to update the atime of the file,
          * so just ignore the return value.
          * We may also fail on filesystems that have the ability to make parts
          * of the fs read only, e.g. subvolumes in Btrfs.
          */
         inode_update_time(inode, S_ATIME);
         mnt_put_write_access(mnt);
 skip_update:
         sb_end_write(inode->i_sb);
 }
 EXPORT_SYMBOL(touch_atime);
 
 /*
  * Return mask of changes for notify_change() that need to be done as a
  * response to write or truncate. Return 0 if nothing has to be changed.
  * Negative value on error (change should be denied).
  */
 int dentry_needs_remove_privs(struct mnt_idmap *idmap,
                               struct dentry *dentry)
 {
         struct inode *inode = d_inode(dentry);
         int mask = 0;
         int ret;
 
         if (IS_NOSEC(inode))
                 return 0;
 
         mask = setattr_should_drop_suidgid(idmap, inode);
         ret = security_inode_need_killpriv(dentry);
         if (ret < 0)
                 return ret;
         if (ret)
                 mask |= ATTR_KILL_PRIV;
         return mask;
 }
 
 static int __remove_privs(struct mnt_idmap *idmap,
                           struct dentry *dentry, int kill)
 {
         struct iattr newattrs;
 
         newattrs.ia_valid = ATTR_FORCE | kill;
         /*
          * Note we call this on write, so notify_change will not
          * encounter any conflicting delegations:
          */
         return notify_change(idmap, dentry, &newattrs, NULL);
 }
 
 int file_remove_privs_flags(struct file *file, unsigned int flags)
 {
         struct dentry *dentry = file_dentry(file);
         struct inode *inode = file_inode(file);
         int error = 0;
         int kill;
 
         if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
                 return 0;
 
         kill = dentry_needs_remove_privs(file_mnt_idmap(file), dentry);
         if (kill < 0)
                 return kill;
 
         if (kill) {
                 if (flags & IOCB_NOWAIT)
                         return -EAGAIN;
 
                 error = __remove_privs(file_mnt_idmap(file), dentry, kill);
         }
 
         if (!error)
                 inode_has_no_xattr(inode);
         return error;
 }
 EXPORT_SYMBOL_GPL(file_remove_privs_flags);
 
 /**
  * file_remove_privs - remove special file privileges (suid, capabilities)
  * @file: file to remove privileges from
  *
  * When file is modified by a write or truncation ensure that special
  * file privileges are removed.
  *
  * Return: 0 on success, negative errno on failure.
  */
 int file_remove_privs(struct file *file)
 {
         return file_remove_privs_flags(file, 0);
 }
 EXPORT_SYMBOL(file_remove_privs);
 
 static int inode_needs_update_time(struct inode *inode)
 {
         int sync_it = 0;
         struct timespec64 now = current_time(inode);
         struct timespec64 ts;
 
         /* First try to exhaust all avenues to not sync */
         if (IS_NOCMTIME(inode))
                 return 0;
 
         ts = inode_get_mtime(inode);
         if (!timespec64_equal(&ts, &now))
                 sync_it = S_MTIME;
 
         ts = inode_get_ctime(inode);
         if (!timespec64_equal(&ts, &now))
                 sync_it |= S_CTIME;
 
         if (IS_I_VERSION(inode) && inode_iversion_need_inc(inode))
                 sync_it |= S_VERSION;
 
         return sync_it;
 }
 
 static int __file_update_time(struct file *file, int sync_mode)
 {
         int ret = 0;
         struct inode *inode = file_inode(file);
 
         /* try to update time settings */
         if (!mnt_get_write_access_file(file)) {
                 ret = inode_update_time(inode, sync_mode);
                 mnt_put_write_access_file(file);
         }
 
         return ret;
 }
 
 /**
  * file_update_time - update mtime and ctime time
  * @file: file accessed
  *
  * Update the mtime and ctime members of an inode and mark the inode for
  * writeback. Note that this function is meant exclusively for usage in
  * the file write path of filesystems, and filesystems may choose to
  * explicitly ignore updates via this function with the _NOCMTIME inode
  * flag, e.g. for network filesystem where these imestamps are handled
  * by the server. This can return an error for file systems who need to
  * allocate space in order to update an inode.
  *
  * Return: 0 on success, negative errno on failure.
  */
 int file_update_time(struct file *file)
 {
         int ret;
         struct inode *inode = file_inode(file);
 
         ret = inode_needs_update_time(inode);
         if (ret <= 0)
                 return ret;
 
         return __file_update_time(file, ret);
 }
 EXPORT_SYMBOL(file_update_time);
 
 /**
  * file_modified_flags - handle mandated vfs changes when modifying a file
  * @file: file that was modified
  * @flags: kiocb flags
  *
  * When file has been modified ensure that special
  * file privileges are removed and time settings are updated.
  *
  * If IOCB_NOWAIT is set, special file privileges will not be removed and
  * time settings will not be updated. It will return -EAGAIN.
  *
  * Context: Caller must hold the file's inode lock.
  *
  * Return: 0 on success, negative errno on failure.
  */
 static int file_modified_flags(struct file *file, int flags)
 {
         int ret;
         struct inode *inode = file_inode(file);
 
         /*
          * Clear the security bits if the process is not being run by root.
          * This keeps people from modifying setuid and setgid binaries.
          */
         ret = file_remove_privs_flags(file, flags);
         if (ret)
                 return ret;
 
         if (unlikely(file->f_mode & FMODE_NOCMTIME))
                 return 0;
 
         ret = inode_needs_update_time(inode);
         if (ret <= 0)
                 return ret;
         if (flags & IOCB_NOWAIT)
                 return -EAGAIN;
 
         return __file_update_time(file, ret);
 }
 
 /**
  * file_modified - handle mandated vfs changes when modifying a file
  * @file: file that was modified
  *
  * When file has been modified ensure that special
  * file privileges are removed and time settings are updated.
  *
  * Context: Caller must hold the file's inode lock.
  *
  * Return: 0 on success, negative errno on failure.
  */
 int file_modified(struct file *file)
 {
         return file_modified_flags(file, 0);
 }
 EXPORT_SYMBOL(file_modified);
 
 /**
  * kiocb_modified - handle mandated vfs changes when modifying a file
  * @iocb: iocb that was modified
  *
  * When file has been modified ensure that special
  * file privileges are removed and time settings are updated.
  *
  * Context: Caller must hold the file's inode lock.
  *
  * Return: 0 on success, negative errno on failure.
  */
 int kiocb_modified(struct kiocb *iocb)
 {
         return file_modified_flags(iocb->ki_filp, iocb->ki_flags);
 }
 EXPORT_SYMBOL_GPL(kiocb_modified);
 
 int inode_needs_sync(struct inode *inode)
 {
         if (IS_SYNC(inode))
                 return 1;
         if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
                 return 1;
         return 0;
 }
 EXPORT_SYMBOL(inode_needs_sync);
 
 /*
  * If we try to find an inode in the inode hash while it is being
  * deleted, we have to wait until the filesystem completes its
  * deletion before reporting that it isn't found.  This function waits
  * until the deletion _might_ have completed.  Callers are responsible
  * to recheck inode state.
  *
  * It doesn't matter if I_NEW is not set initially, a call to
  * wake_up_bit(&inode->i_state, __I_NEW) after removing from the hash list
  * will DTRT.
  */
 static void __wait_on_freeing_inode(struct inode *inode, bool is_inode_hash_locked)
 {
         wait_queue_head_t *wq;
         DEFINE_WAIT_BIT(wait, &inode->i_state, __I_NEW);
 
         /*
          * Handle racing against evict(), see that routine for more details.
          */
         if (unlikely(inode_unhashed(inode))) {
                 WARN_ON(is_inode_hash_locked);
                 spin_unlock(&inode->i_lock);
                 return;
         }
 
         wq = bit_waitqueue(&inode->i_state, __I_NEW);
         prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
         spin_unlock(&inode->i_lock);
         rcu_read_unlock();
         if (is_inode_hash_locked)
                 spin_unlock(&inode_hash_lock);
         schedule();
         finish_wait(wq, &wait.wq_entry);
         if (is_inode_hash_locked)
                 spin_lock(&inode_hash_lock);
         rcu_read_lock();
 }
 
 static __initdata unsigned long ihash_entries;
 static int __init set_ihash_entries(char *str)
 {
         if (!str)
                 return 0;
         ihash_entries = simple_strtoul(str, &str, 0);
         return 1;
 }
 __setup("ihash_entries=", set_ihash_entries);
 
 /*
  * Initialize the waitqueues and inode hash table.
  */
 void __init inode_init_early(void)
 {
         /* If hashes are distributed across NUMA nodes, defer
          * hash allocation until vmalloc space is available.
          */
         if (hashdist)
                 return;
 
         inode_hashtable =
                 alloc_large_system_hash("Inode-cache",
                                         sizeof(struct hlist_head),
                                         ihash_entries,
                                         14,
                                         HASH_EARLY | HASH_ZERO,
                                         &i_hash_shift,
                                         &i_hash_mask,
                                         0,
                                         0);
 }
 
 void __init inode_init(void)
 {
         /* inode slab cache */
         inode_cachep = kmem_cache_create("inode_cache",
                                          sizeof(struct inode),
                                          0,
                                          (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
                                          SLAB_ACCOUNT),
                                          init_once);
 
         /* Hash may have been set up in inode_init_early */
         if (!hashdist)
                 return;
 
         inode_hashtable =
                 alloc_large_system_hash("Inode-cache",
                                         sizeof(struct hlist_head),
                                         ihash_entries,
                                         14,
                                         HASH_ZERO,
                                         &i_hash_shift,
                                         &i_hash_mask,
                                         0,
                                         0);
 }
 
 void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
 {
         inode->i_mode = mode;
         if (S_ISCHR(mode)) {
                 inode->i_fop = &def_chr_fops;
                 inode->i_rdev = rdev;
         } else if (S_ISBLK(mode)) {
                 if (IS_ENABLED(CONFIG_BLOCK))
                         inode->i_fop = &def_blk_fops;
                 inode->i_rdev = rdev;
         } else if (S_ISFIFO(mode))
                 inode->i_fop = &pipefifo_fops;
         else if (S_ISSOCK(mode))
                 ;       /* leave it no_open_fops */
         else
                 printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o) for"
                                   " inode %s:%lu\n", mode, inode->i_sb->s_id,
                                   inode->i_ino);
 }
 EXPORT_SYMBOL(init_special_inode);
 
 /**
  * inode_init_owner - Init uid,gid,mode for new inode according to posix standards
  * @idmap: idmap of the mount the inode was created from
  * @inode: New inode
  * @dir: Directory inode
  * @mode: mode of the new inode
  *
  * If the inode has been created through an idmapped mount the idmap of
  * the vfsmount must be passed through @idmap. This function will then take
  * care to map the inode according to @idmap before checking permissions
  * and initializing i_uid and i_gid. On non-idmapped mounts or if permission
  * checking is to be performed on the raw inode simply pass @nop_mnt_idmap.
  */
 void inode_init_owner(struct mnt_idmap *idmap, struct inode *inode,
                       const struct inode *dir, umode_t mode)
 {
         inode_fsuid_set(inode, idmap);
         if (dir && dir->i_mode & S_ISGID) {
                 inode->i_gid = dir->i_gid;
 
                 /* Directories are special, and always inherit S_ISGID */
                 if (S_ISDIR(mode))
                         mode |= S_ISGID;
         } else
                 inode_fsgid_set(inode, idmap);
         inode->i_mode = mode;
 }
 EXPORT_SYMBOL(inode_init_owner);
 
 /**
  * inode_owner_or_capable - check current task permissions to inode
  * @idmap: idmap of the mount the inode was found from
  * @inode: inode being checked
  *
  * Return true if current either has CAP_FOWNER in a namespace with the
  * inode owner uid mapped, or owns the file.
  *
  * If the inode has been found through an idmapped mount the idmap of
  * the vfsmount must be passed through @idmap. This function will then take
  * care to map the inode according to @idmap before checking permissions.
  * On non-idmapped mounts or if permission checking is to be performed on the
  * raw inode simply pass @nop_mnt_idmap.
  */
 bool inode_owner_or_capable(struct mnt_idmap *idmap,
                             const struct inode *inode)
 {
         vfsuid_t vfsuid;
         struct user_namespace *ns;
 
         vfsuid = i_uid_into_vfsuid(idmap, inode);
         if (vfsuid_eq_kuid(vfsuid, current_fsuid()))
                 return true;
 
         ns = current_user_ns();
         if (vfsuid_has_mapping(ns, vfsuid) && ns_capable(ns, CAP_FOWNER))
                 return true;
         return false;
 }
 EXPORT_SYMBOL(inode_owner_or_capable);
 
 /*
  * Direct i/o helper functions
  */
 static void __inode_dio_wait(struct inode *inode)
 {
         wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
         DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);
 
         do {
                 prepare_to_wait(wq, &q.wq_entry, TASK_UNINTERRUPTIBLE);
                 if (atomic_read(&inode->i_dio_count))
                         schedule();
         } while (atomic_read(&inode->i_dio_count));
         finish_wait(wq, &q.wq_entry);
 }
 
 /**
  * inode_dio_wait - wait for outstanding DIO requests to finish
  * @inode: inode to wait for
  *
  * Waits for all pending direct I/O requests to finish so that we can
  * proceed with a truncate or equivalent operation.
  *
  * Must be called under a lock that serializes taking new references
  * to i_dio_count, usually by inode->i_mutex.
  */
 void inode_dio_wait(struct inode *inode)
 {
         if (atomic_read(&inode->i_dio_count))
                 __inode_dio_wait(inode);
 }
 EXPORT_SYMBOL(inode_dio_wait);
 
 /*
  * inode_set_flags - atomically set some inode flags
  *
  * Note: the caller should be holding i_mutex, or else be sure that
  * they have exclusive access to the inode structure (i.e., while the
  * inode is being instantiated).  The reason for the cmpxchg() loop
  * --- which wouldn't be necessary if all code paths which modify
  * i_flags actually followed this rule, is that there is at least one
  * code path which doesn't today so we use cmpxchg() out of an abundance
  * of caution.
  *
  * In the long run, i_mutex is overkill, and we should probably look
  * at using the i_lock spinlock to protect i_flags, and then make sure
  * it is so documented in include/linux/fs.h and that all code follows
  * the locking convention!!
  */
 void inode_set_flags(struct inode *inode, unsigned int flags,
                      unsigned int mask)
 {
         WARN_ON_ONCE(flags & ~mask);
         set_mask_bits(&inode->i_flags, mask, flags);
 }
 EXPORT_SYMBOL(inode_set_flags);
 
 void inode_nohighmem(struct inode *inode)
 {
         mapping_set_gfp_mask(inode->i_mapping, GFP_USER);
 }
 EXPORT_SYMBOL(inode_nohighmem);
 
 /**
  * timestamp_truncate - Truncate timespec to a granularity
  * @t: Timespec
  * @inode: inode being updated
  *
  * Truncate a timespec to the granularity supported by the fs
  * containing the inode. Always rounds down. gran must
  * not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns).
  */
 struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode)
 {
         struct super_block *sb = inode->i_sb;
         unsigned int gran = sb->s_time_gran;
 
         t.tv_sec = clamp(t.tv_sec, sb->s_time_min, sb->s_time_max);
         if (unlikely(t.tv_sec == sb->s_time_max || t.tv_sec == sb->s_time_min))
                 t.tv_nsec = 0;
 
         /* Avoid division in the common cases 1 ns and 1 s. */
         if (gran == 1)
                 ; /* nothing */
         else if (gran == NSEC_PER_SEC)
                 t.tv_nsec = 0;
         else if (gran > 1 && gran < NSEC_PER_SEC)
                 t.tv_nsec -= t.tv_nsec % gran;
         else
                 WARN(1, "invalid file time granularity: %u", gran);
         return t;
 }
 EXPORT_SYMBOL(timestamp_truncate);
 
 /**
  * current_time - Return FS time
  * @inode: inode.
  *
  * Return the current time truncated to the time granularity supported by
  * the fs.
  *
  * Note that inode and inode->sb cannot be NULL.
  * Otherwise, the function warns and returns time without truncation.
  */
 struct timespec64 current_time(struct inode *inode)
 {
         struct timespec64 now;
 
         ktime_get_coarse_real_ts64(&now);
         return timestamp_truncate(now, inode);
 }
 EXPORT_SYMBOL(current_time);
 
 /**
  * inode_set_ctime_current - set the ctime to current_time
  * @inode: inode
  *
  * Set the inode->i_ctime to the current value for the inode. Returns
  * the current value that was assigned to i_ctime.
  */
 struct timespec64 inode_set_ctime_current(struct inode *inode)
 {
         struct timespec64 now = current_time(inode);
 
         inode_set_ctime_to_ts(inode, now);
         return now;
 }
 EXPORT_SYMBOL(inode_set_ctime_current);
 
 /**
  * in_group_or_capable - check whether caller is CAP_FSETID privileged
  * @idmap:      idmap of the mount @inode was found from
  * @inode:      inode to check
  * @vfsgid:     the new/current vfsgid of @inode
  *
  * Check wether @vfsgid is in the caller's group list or if the caller is
  * privileged with CAP_FSETID over @inode. This can be used to determine
  * whether the setgid bit can be kept or must be dropped.
  *
  * Return: true if the caller is sufficiently privileged, false if not.
  */
 bool in_group_or_capable(struct mnt_idmap *idmap,
                          const struct inode *inode, vfsgid_t vfsgid)
 {
         if (vfsgid_in_group_p(vfsgid))
                 return true;
         if (capable_wrt_inode_uidgid(idmap, inode, CAP_FSETID))
                 return true;
         return false;
 }
 EXPORT_SYMBOL(in_group_or_capable);
 
 /**
  * mode_strip_sgid - handle the sgid bit for non-directories
  * @idmap: idmap of the mount the inode was created from
  * @dir: parent directory inode
  * @mode: mode of the file to be created in @dir
  *
  * If the @mode of the new file has both the S_ISGID and S_IXGRP bit
  * raised and @dir has the S_ISGID bit raised ensure that the caller is
  * either in the group of the parent directory or they have CAP_FSETID
  * in their user namespace and are privileged over the parent directory.
  * In all other cases, strip the S_ISGID bit from @mode.
  *
  * Return: the new mode to use for the file
  */
 umode_t mode_strip_sgid(struct mnt_idmap *idmap,
                         const struct inode *dir, umode_t mode)
 {
         if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
                 return mode;
         if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
                 return mode;
         if (in_group_or_capable(idmap, dir, i_gid_into_vfsgid(idmap, dir)))
                 return mode;
         return mode & ~S_ISGID;
 }
 EXPORT_SYMBOL(mode_strip_sgid);
 

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.