TOMOYO Linux Cross Reference
Linux/fs/libfs.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    *      fs/libfs.c
    *      Library for filesystems writers.
    */
   
   #include <linux/blkdev.h>
   #include <linux/export.h>
   #include <linux/pagemap.h>
  #include <linux/slab.h>
  #include <linux/cred.h>
  #include <linux/mount.h>
  #include <linux/vfs.h>
  #include <linux/quotaops.h>
  #include <linux/mutex.h>
  #include <linux/namei.h>
  #include <linux/exportfs.h>
  #include <linux/iversion.h>
  #include <linux/writeback.h>
  #include <linux/buffer_head.h> /* sync_mapping_buffers */
  #include <linux/fs_context.h>
  #include <linux/pseudo_fs.h>
  #include <linux/fsnotify.h>
  #include <linux/unicode.h>
  #include <linux/fscrypt.h>
  #include <linux/pidfs.h>
  
  #include <linux/uaccess.h>
  
  #include "internal.h"
  
  int simple_getattr(struct mnt_idmap *idmap, const struct path *path,
                     struct kstat *stat, u32 request_mask,
                     unsigned int query_flags)
  {
          struct inode *inode = d_inode(path->dentry);
          generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
          stat->blocks = inode->i_mapping->nrpages << (PAGE_SHIFT - 9);
          return 0;
  }
  EXPORT_SYMBOL(simple_getattr);
  
  int simple_statfs(struct dentry *dentry, struct kstatfs *buf)
  {
          u64 id = huge_encode_dev(dentry->d_sb->s_dev);
  
          buf->f_fsid = u64_to_fsid(id);
          buf->f_type = dentry->d_sb->s_magic;
          buf->f_bsize = PAGE_SIZE;
          buf->f_namelen = NAME_MAX;
          return 0;
  }
  EXPORT_SYMBOL(simple_statfs);
  
  /*
   * Retaining negative dentries for an in-memory filesystem just wastes
   * memory and lookup time: arrange for them to be deleted immediately.
   */
  int always_delete_dentry(const struct dentry *dentry)
  {
          return 1;
  }
  EXPORT_SYMBOL(always_delete_dentry);
  
  const struct dentry_operations simple_dentry_operations = {
          .d_delete = always_delete_dentry,
  };
  EXPORT_SYMBOL(simple_dentry_operations);
  
  /*
   * Lookup the data. This is trivial - if the dentry didn't already
   * exist, we know it is negative.  Set d_op to delete negative dentries.
   */
  struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
  {
          if (dentry->d_name.len > NAME_MAX)
                  return ERR_PTR(-ENAMETOOLONG);
          if (!dentry->d_sb->s_d_op)
                  d_set_d_op(dentry, &simple_dentry_operations);
          d_add(dentry, NULL);
          return NULL;
  }
  EXPORT_SYMBOL(simple_lookup);
  
  int dcache_dir_open(struct inode *inode, struct file *file)
  {
          file->private_data = d_alloc_cursor(file->f_path.dentry);
  
          return file->private_data ? 0 : -ENOMEM;
  }
  EXPORT_SYMBOL(dcache_dir_open);
  
  int dcache_dir_close(struct inode *inode, struct file *file)
  {
          dput(file->private_data);
          return 0;
  }
  EXPORT_SYMBOL(dcache_dir_close);
  
 /* parent is locked at least shared */
 /*
  * Returns an element of siblings' list.
  * We are looking for <count>th positive after <p>; if
  * found, dentry is grabbed and returned to caller.
  * If no such element exists, NULL is returned.
  */
 static struct dentry *scan_positives(struct dentry *cursor,
                                         struct hlist_node **p,
                                         loff_t count,
                                         struct dentry *last)
 {
         struct dentry *dentry = cursor->d_parent, *found = NULL;
 
         spin_lock(&dentry->d_lock);
         while (*p) {
                 struct dentry *d = hlist_entry(*p, struct dentry, d_sib);
                 p = &d->d_sib.next;
                 // we must at least skip cursors, to avoid livelocks
                 if (d->d_flags & DCACHE_DENTRY_CURSOR)
                         continue;
                 if (simple_positive(d) && !--count) {
                         spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
                         if (simple_positive(d))
                                 found = dget_dlock(d);
                         spin_unlock(&d->d_lock);
                         if (likely(found))
                                 break;
                         count = 1;
                 }
                 if (need_resched()) {
                         if (!hlist_unhashed(&cursor->d_sib))
                                 __hlist_del(&cursor->d_sib);
                         hlist_add_behind(&cursor->d_sib, &d->d_sib);
                         p = &cursor->d_sib.next;
                         spin_unlock(&dentry->d_lock);
                         cond_resched();
                         spin_lock(&dentry->d_lock);
                 }
         }
         spin_unlock(&dentry->d_lock);
         dput(last);
         return found;
 }
 
 loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
 {
         struct dentry *dentry = file->f_path.dentry;
         switch (whence) {
                 case 1:
                         offset += file->f_pos;
                         fallthrough;
                 case 0:
                         if (offset >= 0)
                                 break;
                         fallthrough;
                 default:
                         return -EINVAL;
         }
         if (offset != file->f_pos) {
                 struct dentry *cursor = file->private_data;
                 struct dentry *to = NULL;
 
                 inode_lock_shared(dentry->d_inode);
 
                 if (offset > 2)
                         to = scan_positives(cursor, &dentry->d_children.first,
                                             offset - 2, NULL);
                 spin_lock(&dentry->d_lock);
                 hlist_del_init(&cursor->d_sib);
                 if (to)
                         hlist_add_behind(&cursor->d_sib, &to->d_sib);
                 spin_unlock(&dentry->d_lock);
                 dput(to);
 
                 file->f_pos = offset;
 
                 inode_unlock_shared(dentry->d_inode);
         }
         return offset;
 }
 EXPORT_SYMBOL(dcache_dir_lseek);
 
 /*
  * Directory is locked and all positive dentries in it are safe, since
  * for ramfs-type trees they can't go away without unlink() or rmdir(),
  * both impossible due to the lock on directory.
  */
 
 int dcache_readdir(struct file *file, struct dir_context *ctx)
 {
         struct dentry *dentry = file->f_path.dentry;
         struct dentry *cursor = file->private_data;
         struct dentry *next = NULL;
         struct hlist_node **p;
 
         if (!dir_emit_dots(file, ctx))
                 return 0;
 
         if (ctx->pos == 2)
                 p = &dentry->d_children.first;
         else
                 p = &cursor->d_sib.next;
 
         while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
                 if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
                               d_inode(next)->i_ino,
                               fs_umode_to_dtype(d_inode(next)->i_mode)))
                         break;
                 ctx->pos++;
                 p = &next->d_sib.next;
         }
         spin_lock(&dentry->d_lock);
         hlist_del_init(&cursor->d_sib);
         if (next)
                 hlist_add_before(&cursor->d_sib, &next->d_sib);
         spin_unlock(&dentry->d_lock);
         dput(next);
 
         return 0;
 }
 EXPORT_SYMBOL(dcache_readdir);
 
 ssize_t generic_read_dir(struct file *filp, char __user *buf, size_t siz, loff_t *ppos)
 {
         return -EISDIR;
 }
 EXPORT_SYMBOL(generic_read_dir);
 
 const struct file_operations simple_dir_operations = {
         .open           = dcache_dir_open,
         .release        = dcache_dir_close,
         .llseek         = dcache_dir_lseek,
         .read           = generic_read_dir,
         .iterate_shared = dcache_readdir,
         .fsync          = noop_fsync,
 };
 EXPORT_SYMBOL(simple_dir_operations);
 
 const struct inode_operations simple_dir_inode_operations = {
         .lookup         = simple_lookup,
 };
 EXPORT_SYMBOL(simple_dir_inode_operations);
 
 /* 0 is '.', 1 is '..', so always start with offset 2 or more */
 enum {
         DIR_OFFSET_MIN  = 2,
 };
 
 static void offset_set(struct dentry *dentry, long offset)
 {
         dentry->d_fsdata = (void *)offset;
 }
 
 static long dentry2offset(struct dentry *dentry)
 {
         return (long)dentry->d_fsdata;
 }
 
 static struct lock_class_key simple_offset_lock_class;
 
 /**
  * simple_offset_init - initialize an offset_ctx
  * @octx: directory offset map to be initialized
  *
  */
 void simple_offset_init(struct offset_ctx *octx)
 {
         mt_init_flags(&octx->mt, MT_FLAGS_ALLOC_RANGE);
         lockdep_set_class(&octx->mt.ma_lock, &simple_offset_lock_class);
         octx->next_offset = DIR_OFFSET_MIN;
 }
 
 /**
  * simple_offset_add - Add an entry to a directory's offset map
  * @octx: directory offset ctx to be updated
  * @dentry: new dentry being added
  *
  * Returns zero on success. @octx and the dentry's offset are updated.
  * Otherwise, a negative errno value is returned.
  */
 int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
 {
         unsigned long offset;
         int ret;
 
         if (dentry2offset(dentry) != 0)
                 return -EBUSY;
 
         ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN,
                                  LONG_MAX, &octx->next_offset, GFP_KERNEL);
         if (ret < 0)
                 return ret;
 
         offset_set(dentry, offset);
         return 0;
 }
 
 static int simple_offset_replace(struct offset_ctx *octx, struct dentry *dentry,
                                  long offset)
 {
         int ret;
 
         ret = mtree_store(&octx->mt, offset, dentry, GFP_KERNEL);
         if (ret)
                 return ret;
         offset_set(dentry, offset);
         return 0;
 }
 
 /**
  * simple_offset_remove - Remove an entry to a directory's offset map
  * @octx: directory offset ctx to be updated
  * @dentry: dentry being removed
  *
  */
 void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
 {
         long offset;
 
         offset = dentry2offset(dentry);
         if (offset == 0)
                 return;
 
         mtree_erase(&octx->mt, offset);
         offset_set(dentry, 0);
 }
 
 /**
  * simple_offset_empty - Check if a dentry can be unlinked
  * @dentry: dentry to be tested
  *
  * Returns 0 if @dentry is a non-empty directory; otherwise returns 1.
  */
 int simple_offset_empty(struct dentry *dentry)
 {
         struct inode *inode = d_inode(dentry);
         struct offset_ctx *octx;
         struct dentry *child;
         unsigned long index;
         int ret = 1;
 
         if (!inode || !S_ISDIR(inode->i_mode))
                 return ret;
 
         index = DIR_OFFSET_MIN;
         octx = inode->i_op->get_offset_ctx(inode);
         mt_for_each(&octx->mt, child, index, LONG_MAX) {
                 spin_lock(&child->d_lock);
                 if (simple_positive(child)) {
                         spin_unlock(&child->d_lock);
                         ret = 0;
                         break;
                 }
                 spin_unlock(&child->d_lock);
         }
 
         return ret;
 }
 
 /**
  * simple_offset_rename - handle directory offsets for rename
  * @old_dir: parent directory of source entry
  * @old_dentry: dentry of source entry
  * @new_dir: parent_directory of destination entry
  * @new_dentry: dentry of destination
  *
  * Caller provides appropriate serialization.
  *
  * User space expects the directory offset value of the replaced
  * (new) directory entry to be unchanged after a rename.
  *
  * Returns zero on success, a negative errno value on failure.
  */
 int simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,
                          struct inode *new_dir, struct dentry *new_dentry)
 {
         struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);
         struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);
         long new_offset = dentry2offset(new_dentry);
 
         simple_offset_remove(old_ctx, old_dentry);
 
         if (new_offset) {
                 offset_set(new_dentry, 0);
                 return simple_offset_replace(new_ctx, old_dentry, new_offset);
         }
         return simple_offset_add(new_ctx, old_dentry);
 }
 
 /**
  * simple_offset_rename_exchange - exchange rename with directory offsets
  * @old_dir: parent of dentry being moved
  * @old_dentry: dentry being moved
  * @new_dir: destination parent
  * @new_dentry: destination dentry
  *
  * This API preserves the directory offset values. Caller provides
  * appropriate serialization.
  *
  * Returns zero on success. Otherwise a negative errno is returned and the
  * rename is rolled back.
  */
 int simple_offset_rename_exchange(struct inode *old_dir,
                                   struct dentry *old_dentry,
                                   struct inode *new_dir,
                                   struct dentry *new_dentry)
 {
         struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);
         struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);
         long old_index = dentry2offset(old_dentry);
         long new_index = dentry2offset(new_dentry);
         int ret;
 
         simple_offset_remove(old_ctx, old_dentry);
         simple_offset_remove(new_ctx, new_dentry);
 
         ret = simple_offset_replace(new_ctx, old_dentry, new_index);
         if (ret)
                 goto out_restore;
 
         ret = simple_offset_replace(old_ctx, new_dentry, old_index);
         if (ret) {
                 simple_offset_remove(new_ctx, old_dentry);
                 goto out_restore;
         }
 
         ret = simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
         if (ret) {
                 simple_offset_remove(new_ctx, old_dentry);
                 simple_offset_remove(old_ctx, new_dentry);
                 goto out_restore;
         }
         return 0;
 
 out_restore:
         (void)simple_offset_replace(old_ctx, old_dentry, old_index);
         (void)simple_offset_replace(new_ctx, new_dentry, new_index);
         return ret;
 }
 
 /**
  * simple_offset_destroy - Release offset map
  * @octx: directory offset ctx that is about to be destroyed
  *
  * During fs teardown (eg. umount), a directory's offset map might still
  * contain entries. xa_destroy() cleans out anything that remains.
  */
 void simple_offset_destroy(struct offset_ctx *octx)
 {
         mtree_destroy(&octx->mt);
 }
 
 /**
  * offset_dir_llseek - Advance the read position of a directory descriptor
  * @file: an open directory whose position is to be updated
  * @offset: a byte offset
  * @whence: enumerator describing the starting position for this update
  *
  * SEEK_END, SEEK_DATA, and SEEK_HOLE are not supported for directories.
  *
  * Returns the updated read position if successful; otherwise a
  * negative errno is returned and the read position remains unchanged.
  */
 static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence)
 {
         switch (whence) {
         case SEEK_CUR:
                 offset += file->f_pos;
                 fallthrough;
         case SEEK_SET:
                 if (offset >= 0)
                         break;
                 fallthrough;
         default:
                 return -EINVAL;
         }
 
         /* In this case, ->private_data is protected by f_pos_lock */
         file->private_data = NULL;
         return vfs_setpos(file, offset, LONG_MAX);
 }
 
 static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset)
 {
         MA_STATE(mas, &octx->mt, offset, offset);
         struct dentry *child, *found = NULL;
 
         rcu_read_lock();
         child = mas_find(&mas, LONG_MAX);
         if (!child)
                 goto out;
         spin_lock(&child->d_lock);
         if (simple_positive(child))
                 found = dget_dlock(child);
         spin_unlock(&child->d_lock);
 out:
         rcu_read_unlock();
         return found;
 }
 
 static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry)
 {
         struct inode *inode = d_inode(dentry);
         long offset = dentry2offset(dentry);
 
         return ctx->actor(ctx, dentry->d_name.name, dentry->d_name.len, offset,
                           inode->i_ino, fs_umode_to_dtype(inode->i_mode));
 }
 
 static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx)
 {
         struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode);
         struct dentry *dentry;
 
         while (true) {
                 dentry = offset_find_next(octx, ctx->pos);
                 if (!dentry)
                         return ERR_PTR(-ENOENT);
 
                 if (!offset_dir_emit(ctx, dentry)) {
                         dput(dentry);
                         break;
                 }
 
                 ctx->pos = dentry2offset(dentry) + 1;
                 dput(dentry);
         }
         return NULL;
 }
 
 /**
  * offset_readdir - Emit entries starting at offset @ctx->pos
  * @file: an open directory to iterate over
  * @ctx: directory iteration context
  *
  * Caller must hold @file's i_rwsem to prevent insertion or removal of
  * entries during this call.
  *
  * On entry, @ctx->pos contains an offset that represents the first entry
  * to be read from the directory.
  *
  * The operation continues until there are no more entries to read, or
  * until the ctx->actor indicates there is no more space in the caller's
  * output buffer.
  *
  * On return, @ctx->pos contains an offset that will read the next entry
  * in this directory when offset_readdir() is called again with @ctx.
  *
  * Return values:
  *   %0 - Complete
  */
 static int offset_readdir(struct file *file, struct dir_context *ctx)
 {
         struct dentry *dir = file->f_path.dentry;
 
         lockdep_assert_held(&d_inode(dir)->i_rwsem);
 
         if (!dir_emit_dots(file, ctx))
                 return 0;
 
         /* In this case, ->private_data is protected by f_pos_lock */
         if (ctx->pos == DIR_OFFSET_MIN)
                 file->private_data = NULL;
         else if (file->private_data == ERR_PTR(-ENOENT))
                 return 0;
         file->private_data = offset_iterate_dir(d_inode(dir), ctx);
         return 0;
 }
 
 const struct file_operations simple_offset_dir_operations = {
         .llseek         = offset_dir_llseek,
         .iterate_shared = offset_readdir,
         .read           = generic_read_dir,
         .fsync          = noop_fsync,
 };
 
 static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev)
 {
         struct dentry *child = NULL, *d;
 
         spin_lock(&parent->d_lock);
         d = prev ? d_next_sibling(prev) : d_first_child(parent);
         hlist_for_each_entry_from(d, d_sib) {
                 if (simple_positive(d)) {
                         spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
                         if (simple_positive(d))
                                 child = dget_dlock(d);
                         spin_unlock(&d->d_lock);
                         if (likely(child))
                                 break;
                 }
         }
         spin_unlock(&parent->d_lock);
         dput(prev);
         return child;
 }
 
 void simple_recursive_removal(struct dentry *dentry,
                               void (*callback)(struct dentry *))
 {
         struct dentry *this = dget(dentry);
         while (true) {
                 struct dentry *victim = NULL, *child;
                 struct inode *inode = this->d_inode;
 
                 inode_lock(inode);
                 if (d_is_dir(this))
                         inode->i_flags |= S_DEAD;
                 while ((child = find_next_child(this, victim)) == NULL) {
                         // kill and ascend
                         // update metadata while it's still locked
                         inode_set_ctime_current(inode);
                         clear_nlink(inode);
                         inode_unlock(inode);
                         victim = this;
                         this = this->d_parent;
                         inode = this->d_inode;
                         inode_lock(inode);
                         if (simple_positive(victim)) {
                                 d_invalidate(victim);   // avoid lost mounts
                                 if (d_is_dir(victim))
                                         fsnotify_rmdir(inode, victim);
                                 else
                                         fsnotify_unlink(inode, victim);
                                 if (callback)
                                         callback(victim);
                                 dput(victim);           // unpin it
                         }
                         if (victim == dentry) {
                                 inode_set_mtime_to_ts(inode,
                                                       inode_set_ctime_current(inode));
                                 if (d_is_dir(dentry))
                                         drop_nlink(inode);
                                 inode_unlock(inode);
                                 dput(dentry);
                                 return;
                         }
                 }
                 inode_unlock(inode);
                 this = child;
         }
 }
 EXPORT_SYMBOL(simple_recursive_removal);
 
 static const struct super_operations simple_super_operations = {
         .statfs         = simple_statfs,
 };
 
 static int pseudo_fs_fill_super(struct super_block *s, struct fs_context *fc)
 {
         struct pseudo_fs_context *ctx = fc->fs_private;
         struct inode *root;
 
         s->s_maxbytes = MAX_LFS_FILESIZE;
         s->s_blocksize = PAGE_SIZE;
         s->s_blocksize_bits = PAGE_SHIFT;
         s->s_magic = ctx->magic;
         s->s_op = ctx->ops ?: &simple_super_operations;
         s->s_xattr = ctx->xattr;
         s->s_time_gran = 1;
         root = new_inode(s);
         if (!root)
                 return -ENOMEM;
 
         /*
          * since this is the first inode, make it number 1. New inodes created
          * after this must take care not to collide with it (by passing
          * max_reserved of 1 to iunique).
          */
         root->i_ino = 1;
         root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
         simple_inode_init_ts(root);
         s->s_root = d_make_root(root);
         if (!s->s_root)
                 return -ENOMEM;
         s->s_d_op = ctx->dops;
         return 0;
 }
 
 static int pseudo_fs_get_tree(struct fs_context *fc)
 {
         return get_tree_nodev(fc, pseudo_fs_fill_super);
 }
 
 static void pseudo_fs_free(struct fs_context *fc)
 {
         kfree(fc->fs_private);
 }
 
 static const struct fs_context_operations pseudo_fs_context_ops = {
         .free           = pseudo_fs_free,
         .get_tree       = pseudo_fs_get_tree,
 };
 
 /*
  * Common helper for pseudo-filesystems (sockfs, pipefs, bdev - stuff that
  * will never be mountable)
  */
 struct pseudo_fs_context *init_pseudo(struct fs_context *fc,
                                         unsigned long magic)
 {
         struct pseudo_fs_context *ctx;
 
         ctx = kzalloc(sizeof(struct pseudo_fs_context), GFP_KERNEL);
         if (likely(ctx)) {
                 ctx->magic = magic;
                 fc->fs_private = ctx;
                 fc->ops = &pseudo_fs_context_ops;
                 fc->sb_flags |= SB_NOUSER;
                 fc->global = true;
         }
         return ctx;
 }
 EXPORT_SYMBOL(init_pseudo);
 
 int simple_open(struct inode *inode, struct file *file)
 {
         if (inode->i_private)
                 file->private_data = inode->i_private;
         return 0;
 }
 EXPORT_SYMBOL(simple_open);
 
 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode = d_inode(old_dentry);
 
         inode_set_mtime_to_ts(dir,
                               inode_set_ctime_to_ts(dir, inode_set_ctime_current(inode)));
         inc_nlink(inode);
         ihold(inode);
         dget(dentry);
         d_instantiate(dentry, inode);
         return 0;
 }
 EXPORT_SYMBOL(simple_link);
 
 int simple_empty(struct dentry *dentry)
 {
         struct dentry *child;
         int ret = 0;
 
         spin_lock(&dentry->d_lock);
         hlist_for_each_entry(child, &dentry->d_children, d_sib) {
                 spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
                 if (simple_positive(child)) {
                         spin_unlock(&child->d_lock);
                         goto out;
                 }
                 spin_unlock(&child->d_lock);
         }
         ret = 1;
 out:
         spin_unlock(&dentry->d_lock);
         return ret;
 }
 EXPORT_SYMBOL(simple_empty);
 
 int simple_unlink(struct inode *dir, struct dentry *dentry)
 {
         struct inode *inode = d_inode(dentry);
 
         inode_set_mtime_to_ts(dir,
                               inode_set_ctime_to_ts(dir, inode_set_ctime_current(inode)));
         drop_nlink(inode);
         dput(dentry);
         return 0;
 }
 EXPORT_SYMBOL(simple_unlink);
 
 int simple_rmdir(struct inode *dir, struct dentry *dentry)
 {
         if (!simple_empty(dentry))
                 return -ENOTEMPTY;
 
         drop_nlink(d_inode(dentry));
         simple_unlink(dir, dentry);
         drop_nlink(dir);
         return 0;
 }
 EXPORT_SYMBOL(simple_rmdir);
 
 /**
  * simple_rename_timestamp - update the various inode timestamps for rename
  * @old_dir: old parent directory
  * @old_dentry: dentry that is being renamed
  * @new_dir: new parent directory
  * @new_dentry: target for rename
  *
  * POSIX mandates that the old and new parent directories have their ctime and
  * mtime updated, and that inodes of @old_dentry and @new_dentry (if any), have
  * their ctime updated.
  */
 void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
                              struct inode *new_dir, struct dentry *new_dentry)
 {
         struct inode *newino = d_inode(new_dentry);
 
         inode_set_mtime_to_ts(old_dir, inode_set_ctime_current(old_dir));
         if (new_dir != old_dir)
                 inode_set_mtime_to_ts(new_dir,
                                       inode_set_ctime_current(new_dir));
         inode_set_ctime_current(d_inode(old_dentry));
         if (newino)
                 inode_set_ctime_current(newino);
 }
 EXPORT_SYMBOL_GPL(simple_rename_timestamp);
 
 int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
                            struct inode *new_dir, struct dentry *new_dentry)
 {
         bool old_is_dir = d_is_dir(old_dentry);
         bool new_is_dir = d_is_dir(new_dentry);
 
         if (old_dir != new_dir && old_is_dir != new_is_dir) {
                 if (old_is_dir) {
                         drop_nlink(old_dir);
                         inc_nlink(new_dir);
                 } else {
                         drop_nlink(new_dir);
                         inc_nlink(old_dir);
                 }
         }
         simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
         return 0;
 }
 EXPORT_SYMBOL_GPL(simple_rename_exchange);
 
 int simple_rename(struct mnt_idmap *idmap, struct inode *old_dir,
                   struct dentry *old_dentry, struct inode *new_dir,
                   struct dentry *new_dentry, unsigned int flags)
 {
         int they_are_dirs = d_is_dir(old_dentry);
 
         if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
                 return -EINVAL;
 
         if (flags & RENAME_EXCHANGE)
                 return simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
 
         if (!simple_empty(new_dentry))
                 return -ENOTEMPTY;
 
         if (d_really_is_positive(new_dentry)) {
                 simple_unlink(new_dir, new_dentry);
                 if (they_are_dirs) {
                         drop_nlink(d_inode(new_dentry));
                         drop_nlink(old_dir);
                 }
         } else if (they_are_dirs) {
                 drop_nlink(old_dir);
                 inc_nlink(new_dir);
         }
 
         simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
         return 0;
 }
 EXPORT_SYMBOL(simple_rename);
 
 /**
  * simple_setattr - setattr for simple filesystem
  * @idmap: idmap of the target mount
  * @dentry: dentry
  * @iattr: iattr structure
  *
  * Returns 0 on success, -error on failure.
  *
  * simple_setattr is a simple ->setattr implementation without a proper
  * implementation of size changes.
  *
  * It can either be used for in-memory filesystems or special files
  * on simple regular filesystems.  Anything that needs to change on-disk
  * or wire state on size changes needs its own setattr method.
  */
 int simple_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
                    struct iattr *iattr)
 {
         struct inode *inode = d_inode(dentry);
         int error;
 
         error = setattr_prepare(idmap, dentry, iattr);
         if (error)
                 return error;
 
         if (iattr->ia_valid & ATTR_SIZE)
                 truncate_setsize(inode, iattr->ia_size);
         setattr_copy(idmap, inode, iattr);
         mark_inode_dirty(inode);
         return 0;
 }
 EXPORT_SYMBOL(simple_setattr);
 
 static int simple_read_folio(struct file *file, struct folio *folio)
 {
         folio_zero_range(folio, 0, folio_size(folio));
         flush_dcache_folio(folio);
         folio_mark_uptodate(folio);
         folio_unlock(folio);
         return 0;
 }
 
 int simple_write_begin(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len,
                         struct page **pagep, void **fsdata)
 {
         struct folio *folio;
 
         folio = __filemap_get_folio(mapping, pos / PAGE_SIZE, FGP_WRITEBEGIN,
                         mapping_gfp_mask(mapping));
         if (IS_ERR(folio))
                 return PTR_ERR(folio);
 
         *pagep = &folio->page;
 
         if (!folio_test_uptodate(folio) && (len != folio_size(folio))) {
                 size_t from = offset_in_folio(folio, pos);
 
                 folio_zero_segments(folio, 0, from,
                                 from + len, folio_size(folio));
         }
         return 0;
 }
 EXPORT_SYMBOL(simple_write_begin);
 
 /**
  * simple_write_end - .write_end helper for non-block-device FSes
  * @file: See .write_end of address_space_operations
  * @mapping:            "
  * @pos:                "
  * @len:                "
  * @copied:             "
  * @page:               "
  * @fsdata:             "
  *
  * simple_write_end does the minimum needed for updating a page after writing is
  * done. It has the same API signature as the .write_end of
  * address_space_operations vector. So it can just be set onto .write_end for
  * FSes that don't need any other processing. i_mutex is assumed to be held.
  * Block based filesystems should use generic_write_end().
  * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
  * is not called, so a filesystem that actually does store data in .write_inode
  * should extend on what's done here with a call to mark_inode_dirty() in the
  * case that i_size has changed.
  *
  * Use *ONLY* with simple_read_folio()
  */
 static int simple_write_end(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len, unsigned copied,
                         struct page *page, void *fsdata)
 {
         struct folio *folio = page_folio(page);
         struct inode *inode = folio->mapping->host;
         loff_t last_pos = pos + copied;
 
         /* zero the stale part of the folio if we did a short copy */
         if (!folio_test_uptodate(folio)) {
                 if (copied < len) {
                         size_t from = offset_in_folio(folio, pos);
 
                         folio_zero_range(folio, from + copied, len - copied);
                 }
                 folio_mark_uptodate(folio);
         }
         /*
          * No need to use i_size_read() here, the i_size
          * cannot change under us because we hold the i_mutex.
          */
         if (last_pos > inode->i_size)
                 i_size_write(inode, last_pos);
 
         folio_mark_dirty(folio);
         folio_unlock(folio);
         folio_put(folio);
 
         return copied;
 }
 
 /*
  * Provides ramfs-style behavior: data in the pagecache, but no writeback.
  */
 const struct address_space_operations ram_aops = {
         .read_folio     = simple_read_folio,
         .write_begin    = simple_write_begin,
         .write_end      = simple_write_end,
         .dirty_folio    = noop_dirty_folio,
 };
 EXPORT_SYMBOL(ram_aops);
 
 /*
  * the inodes created here are not hashed. If you use iunique to generate
  * unique inode values later for this filesystem, then you must take care
  * to pass it an appropriate max_reserved value to avoid collisions.
  */
 int simple_fill_super(struct super_block *s, unsigned long magic,
                       const struct tree_descr *files)
 {
         struct inode *inode;
         struct dentry *dentry;
         int i;
 
         s->s_blocksize = PAGE_SIZE;
         s->s_blocksize_bits = PAGE_SHIFT;
         s->s_magic = magic;
         s->s_op = &simple_super_operations;
         s->s_time_gran = 1;
 
         inode = new_inode(s);
         if (!inode)
                 return -ENOMEM;
         /*
          * because the root inode is 1, the files array must not contain an
          * entry at index 1
          */
         inode->i_ino = 1;
         inode->i_mode = S_IFDIR | 0755;
         simple_inode_init_ts(inode);
         inode->i_op = &simple_dir_inode_operations;
         inode->i_fop = &simple_dir_operations;
         set_nlink(inode, 2);
         s->s_root = d_make_root(inode);
         if (!s->s_root)
                 return -ENOMEM;
         for (i = 0; !files->name || files->name[0]; i++, files++) {
                 if (!files->name)
                         continue;
 
                 /* warn if it tries to conflict with the root inode */
                 if (unlikely(i == 1))
                         printk(KERN_WARNING "%s: %s passed in a files array"
                                 "with an index of 1!\n", __func__,
                                 s->s_type->name);
 
                 dentry = d_alloc_name(s->s_root, files->name);
                 if (!dentry)
                         return -ENOMEM;
                 inode = new_inode(s);
                 if (!inode) {
                         dput(dentry);
                         return -ENOMEM;
                 }
                 inode->i_mode = S_IFREG | files->mode;
                 simple_inode_init_ts(inode);
                 inode->i_fop = files->ops;
                 inode->i_ino = i;
                 d_add(dentry, inode);
         }
         return 0;
 }
 EXPORT_SYMBOL(simple_fill_super);
 
 static DEFINE_SPINLOCK(pin_fs_lock);
 
 int simple_pin_fs(struct file_system_type *type, struct vfsmount **mount, int *count)
 {
         struct vfsmount *mnt = NULL;
         spin_lock(&pin_fs_lock);
         if (unlikely(!*mount)) {
                 spin_unlock(&pin_fs_lock);
                 mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
                 if (IS_ERR(mnt))
                         return PTR_ERR(mnt);
                 spin_lock(&pin_fs_lock);
                 if (!*mount)
                         *mount = mnt;
         }
         mntget(*mount);
         ++*count;
         spin_unlock(&pin_fs_lock);
         mntput(mnt);
         return 0;
 }
 EXPORT_SYMBOL(simple_pin_fs);
 
 void simple_release_fs(struct vfsmount **mount, int *count)
 {
         struct vfsmount *mnt;
         spin_lock(&pin_fs_lock);
         mnt = *mount;
         if (!--*count)
                 *mount = NULL;
         spin_unlock(&pin_fs_lock);
         mntput(mnt);
 }
 EXPORT_SYMBOL(simple_release_fs);
 
 /**
  * simple_read_from_buffer - copy data from the buffer to user space
  * @to: the user space buffer to read to
  * @count: the maximum number of bytes to read
  * @ppos: the current position in the buffer
  * @from: the buffer to read from
  * @available: the size of the buffer
  *
  * The simple_read_from_buffer() function reads up to @count bytes from the
  * buffer @from at offset @ppos into the user space address starting at @to.
  *
  * On success, the number of bytes read is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
                                 const void *from, size_t available)
 {
         loff_t pos = *ppos;
         size_t ret;
 
         if (pos < 0)
                 return -EINVAL;
         if (pos >= available || !count)
                 return 0;
         if (count > available - pos)
                 count = available - pos;
         ret = copy_to_user(to, from + pos, count);
         if (ret == count)
                 return -EFAULT;
         count -= ret;
         *ppos = pos + count;
         return count;
 }
 EXPORT_SYMBOL(simple_read_from_buffer);
 
 /**
  * simple_write_to_buffer - copy data from user space to the buffer
  * @to: the buffer to write to
  * @available: the size of the buffer
  * @ppos: the current position in the buffer
  * @from: the user space buffer to read from
  * @count: the maximum number of bytes to read
  *
  * The simple_write_to_buffer() function reads up to @count bytes from the user
  * space address starting at @from into the buffer @to at offset @ppos.
  *
  * On success, the number of bytes written is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
                 const void __user *from, size_t count)
 {
         loff_t pos = *ppos;
         size_t res;
 
         if (pos < 0)
                 return -EINVAL;
         if (pos >= available || !count)
                 return 0;
         if (count > available - pos)
                 count = available - pos;
         res = copy_from_user(to + pos, from, count);
         if (res == count)
                 return -EFAULT;
         count -= res;
         *ppos = pos + count;
         return count;
 }
 EXPORT_SYMBOL(simple_write_to_buffer);
 
 /**
  * memory_read_from_buffer - copy data from the buffer
  * @to: the kernel space buffer to read to
  * @count: the maximum number of bytes to read
  * @ppos: the current position in the buffer
  * @from: the buffer to read from
  * @available: the size of the buffer
  *
  * The memory_read_from_buffer() function reads up to @count bytes from the
  * buffer @from at offset @ppos into the kernel space address starting at @to.
  *
  * On success, the number of bytes read is returned and the offset @ppos is
  * advanced by this number, or negative value is returned on error.
  **/
 ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
                                 const void *from, size_t available)
 {
         loff_t pos = *ppos;
 
         if (pos < 0)
                 return -EINVAL;
         if (pos >= available)
                 return 0;
         if (count > available - pos)
                 count = available - pos;
         memcpy(to, from + pos, count);
         *ppos = pos + count;
 
         return count;
 }
 EXPORT_SYMBOL(memory_read_from_buffer);
 
 /*
  * Transaction based IO.
  * The file expects a single write which triggers the transaction, and then
  * possibly a read which collects the result - which is stored in a
  * file-local buffer.
  */
 
 void simple_transaction_set(struct file *file, size_t n)
 {
         struct simple_transaction_argresp *ar = file->private_data;
 
         BUG_ON(n > SIMPLE_TRANSACTION_LIMIT);
 
         /*
          * The barrier ensures that ar->size will really remain zero until
          * ar->data is ready for reading.
          */
         smp_mb();
         ar->size = n;
 }
 EXPORT_SYMBOL(simple_transaction_set);
 
 char *simple_transaction_get(struct file *file, const char __user *buf, size_t size)
 {
         struct simple_transaction_argresp *ar;
         static DEFINE_SPINLOCK(simple_transaction_lock);
 
         if (size > SIMPLE_TRANSACTION_LIMIT - 1)
                 return ERR_PTR(-EFBIG);
 
         ar = (struct simple_transaction_argresp *)get_zeroed_page(GFP_KERNEL);
         if (!ar)
                 return ERR_PTR(-ENOMEM);
 
         spin_lock(&simple_transaction_lock);
 
         /* only one write allowed per open */
         if (file->private_data) {
                 spin_unlock(&simple_transaction_lock);
                 free_page((unsigned long)ar);
                 return ERR_PTR(-EBUSY);
         }
 
         file->private_data = ar;
 
         spin_unlock(&simple_transaction_lock);
 
         if (copy_from_user(ar->data, buf, size))
                 return ERR_PTR(-EFAULT);
 
         return ar->data;
 }
 EXPORT_SYMBOL(simple_transaction_get);
 
 ssize_t simple_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
 {
         struct simple_transaction_argresp *ar = file->private_data;
 
         if (!ar)
                 return 0;
         return simple_read_from_buffer(buf, size, pos, ar->data, ar->size);
 }
 EXPORT_SYMBOL(simple_transaction_read);
 
 int simple_transaction_release(struct inode *inode, struct file *file)
 {
         free_page((unsigned long)file->private_data);
         return 0;
 }
 EXPORT_SYMBOL(simple_transaction_release);
 
 /* Simple attribute files */
 
 struct simple_attr {
         int (*get)(void *, u64 *);
         int (*set)(void *, u64);
         char get_buf[24];       /* enough to store a u64 and "\n\0" */
         char set_buf[24];
         void *data;
         const char *fmt;        /* format for read operation */
         struct mutex mutex;     /* protects access to these buffers */
 };
 
 /* simple_attr_open is called by an actual attribute open file operation
  * to set the attribute specific access operations. */
 int simple_attr_open(struct inode *inode, struct file *file,
                      int (*get)(void *, u64 *), int (*set)(void *, u64),
                      const char *fmt)
 {
         struct simple_attr *attr;
 
         attr = kzalloc(sizeof(*attr), GFP_KERNEL);
         if (!attr)
                 return -ENOMEM;
 
         attr->get = get;
         attr->set = set;
         attr->data = inode->i_private;
         attr->fmt = fmt;
         mutex_init(&attr->mutex);
 
         file->private_data = attr;
 
         return nonseekable_open(inode, file);
 }
 EXPORT_SYMBOL_GPL(simple_attr_open);
 
 int simple_attr_release(struct inode *inode, struct file *file)
 {
         kfree(file->private_data);
         return 0;
 }
 EXPORT_SYMBOL_GPL(simple_attr_release); /* GPL-only?  This?  Really? */
 
 /* read from the buffer that is filled with the get function */
 ssize_t simple_attr_read(struct file *file, char __user *buf,
                          size_t len, loff_t *ppos)
 {
         struct simple_attr *attr;
         size_t size;
         ssize_t ret;
 
         attr = file->private_data;
 
         if (!attr->get)
                 return -EACCES;
 
         ret = mutex_lock_interruptible(&attr->mutex);
         if (ret)
                 return ret;
 
         if (*ppos && attr->get_buf[0]) {
                 /* continued read */
                 size = strlen(attr->get_buf);
         } else {
                 /* first read */
                 u64 val;
                 ret = attr->get(attr->data, &val);
                 if (ret)
                         goto out;
 
                 size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
                                  attr->fmt, (unsigned long long)val);
         }
 
         ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
 out:
         mutex_unlock(&attr->mutex);
         return ret;
 }
 EXPORT_SYMBOL_GPL(simple_attr_read);
 
 /* interpret the buffer as a number to call the set function with */
 static ssize_t simple_attr_write_xsigned(struct file *file, const char __user *buf,
                           size_t len, loff_t *ppos, bool is_signed)
 {
         struct simple_attr *attr;
         unsigned long long val;
         size_t size;
         ssize_t ret;
 
         attr = file->private_data;
         if (!attr->set)
                 return -EACCES;
 
         ret = mutex_lock_interruptible(&attr->mutex);
         if (ret)
                 return ret;
 
         ret = -EFAULT;
         size = min(sizeof(attr->set_buf) - 1, len);
         if (copy_from_user(attr->set_buf, buf, size))
                 goto out;
 
         attr->set_buf[size] = '\0';
         if (is_signed)
                 ret = kstrtoll(attr->set_buf, 0, &val);
         else
                 ret = kstrtoull(attr->set_buf, 0, &val);
         if (ret)
                 goto out;
         ret = attr->set(attr->data, val);
         if (ret == 0)
                 ret = len; /* on success, claim we got the whole input */
 out:
         mutex_unlock(&attr->mutex);
         return ret;
 }
 
 ssize_t simple_attr_write(struct file *file, const char __user *buf,
                           size_t len, loff_t *ppos)
 {
         return simple_attr_write_xsigned(file, buf, len, ppos, false);
 }
 EXPORT_SYMBOL_GPL(simple_attr_write);
 
 ssize_t simple_attr_write_signed(struct file *file, const char __user *buf,
                           size_t len, loff_t *ppos)
 {
         return simple_attr_write_xsigned(file, buf, len, ppos, true);
 }
 EXPORT_SYMBOL_GPL(simple_attr_write_signed);
 
 /**
  * generic_encode_ino32_fh - generic export_operations->encode_fh function
  * @inode:   the object to encode
  * @fh:      where to store the file handle fragment
  * @max_len: maximum length to store there (in 4 byte units)
  * @parent:  parent directory inode, if wanted
  *
  * This generic encode_fh function assumes that the 32 inode number
  * is suitable for locating an inode, and that the generation number
  * can be used to check that it is still valid.  It places them in the
  * filehandle fragment where export_decode_fh expects to find them.
  */
 int generic_encode_ino32_fh(struct inode *inode, __u32 *fh, int *max_len,
                             struct inode *parent)
 {
         struct fid *fid = (void *)fh;
         int len = *max_len;
         int type = FILEID_INO32_GEN;
 
         if (parent && (len < 4)) {
                 *max_len = 4;
                 return FILEID_INVALID;
         } else if (len < 2) {
                 *max_len = 2;
                 return FILEID_INVALID;
         }
 
         len = 2;
         fid->i32.ino = inode->i_ino;
         fid->i32.gen = inode->i_generation;
         if (parent) {
                 fid->i32.parent_ino = parent->i_ino;
                 fid->i32.parent_gen = parent->i_generation;
                 len = 4;
                 type = FILEID_INO32_GEN_PARENT;
         }
         *max_len = len;
         return type;
 }
 EXPORT_SYMBOL_GPL(generic_encode_ino32_fh);
 
 /**
  * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
  * @sb:         filesystem to do the file handle conversion on
  * @fid:        file handle to convert
  * @fh_len:     length of the file handle in bytes
  * @fh_type:    type of file handle
  * @get_inode:  filesystem callback to retrieve inode
  *
  * This function decodes @fid as long as it has one of the well-known
  * Linux filehandle types and calls @get_inode on it to retrieve the
  * inode for the object specified in the file handle.
  */
 struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
                 int fh_len, int fh_type, struct inode *(*get_inode)
                         (struct super_block *sb, u64 ino, u32 gen))
 {
         struct inode *inode = NULL;
 
         if (fh_len < 2)
                 return NULL;
 
         switch (fh_type) {
         case FILEID_INO32_GEN:
         case FILEID_INO32_GEN_PARENT:
                 inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
                 break;
         }
 
         return d_obtain_alias(inode);
 }
 EXPORT_SYMBOL_GPL(generic_fh_to_dentry);
 
 /**
  * generic_fh_to_parent - generic helper for the fh_to_parent export operation
  * @sb:         filesystem to do the file handle conversion on
  * @fid:        file handle to convert
  * @fh_len:     length of the file handle in bytes
  * @fh_type:    type of file handle
  * @get_inode:  filesystem callback to retrieve inode
  *
  * This function decodes @fid as long as it has one of the well-known
  * Linux filehandle types and calls @get_inode on it to retrieve the
  * inode for the _parent_ object specified in the file handle if it
  * is specified in the file handle, or NULL otherwise.
  */
 struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
                 int fh_len, int fh_type, struct inode *(*get_inode)
                         (struct super_block *sb, u64 ino, u32 gen))
 {
         struct inode *inode = NULL;
 
         if (fh_len <= 2)
                 return NULL;
 
         switch (fh_type) {
         case FILEID_INO32_GEN_PARENT:
                 inode = get_inode(sb, fid->i32.parent_ino,
                                   (fh_len > 3 ? fid->i32.parent_gen : 0));
                 break;
         }
 
         return d_obtain_alias(inode);
 }
 EXPORT_SYMBOL_GPL(generic_fh_to_parent);
 
 /**
  * __generic_file_fsync - generic fsync implementation for simple filesystems
  *
  * @file:       file to synchronize
  * @start:      start offset in bytes
  * @end:        end offset in bytes (inclusive)
  * @datasync:   only synchronize essential metadata if true
  *
  * This is a generic implementation of the fsync method for simple
  * filesystems which track all non-inode metadata in the buffers list
  * hanging off the address_space structure.
  */
 int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
                                  int datasync)
 {
         struct inode *inode = file->f_mapping->host;
         int err;
         int ret;
 
         err = file_write_and_wait_range(file, start, end);
         if (err)
                 return err;
 
         inode_lock(inode);
         ret = sync_mapping_buffers(inode->i_mapping);
         if (!(inode->i_state & I_DIRTY_ALL))
                 goto out;
         if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
                 goto out;
 
         err = sync_inode_metadata(inode, 1);
         if (ret == 0)
                 ret = err;
 
 out:
         inode_unlock(inode);
         /* check and advance again to catch errors after syncing out buffers */
         err = file_check_and_advance_wb_err(file);
         if (ret == 0)
                 ret = err;
         return ret;
 }
 EXPORT_SYMBOL(__generic_file_fsync);
 
 /**
  * generic_file_fsync - generic fsync implementation for simple filesystems
  *                      with flush
  * @file:       file to synchronize
  * @start:      start offset in bytes
  * @end:        end offset in bytes (inclusive)
  * @datasync:   only synchronize essential metadata if true
  *
  */
 
 int generic_file_fsync(struct file *file, loff_t start, loff_t end,
                        int datasync)
 {
         struct inode *inode = file->f_mapping->host;
         int err;
 
         err = __generic_file_fsync(file, start, end, datasync);
         if (err)
                 return err;
         return blkdev_issue_flush(inode->i_sb->s_bdev);
 }
 EXPORT_SYMBOL(generic_file_fsync);
 
 /**
  * generic_check_addressable - Check addressability of file system
  * @blocksize_bits:     log of file system block size
  * @num_blocks:         number of blocks in file system
  *
  * Determine whether a file system with @num_blocks blocks (and a
  * block size of 2**@blocksize_bits) is addressable by the sector_t
  * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
  */
 int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
 {
         u64 last_fs_block = num_blocks - 1;
         u64 last_fs_page =
                 last_fs_block >> (PAGE_SHIFT - blocksize_bits);
 
         if (unlikely(num_blocks == 0))
                 return 0;
 
         if ((blocksize_bits < 9) || (blocksize_bits > PAGE_SHIFT))
                 return -EINVAL;
 
         if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
             (last_fs_page > (pgoff_t)(~0ULL))) {
                 return -EFBIG;
         }
         return 0;
 }
 EXPORT_SYMBOL(generic_check_addressable);
 
 /*
  * No-op implementation of ->fsync for in-memory filesystems.
  */
 int noop_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
         return 0;
 }
 EXPORT_SYMBOL(noop_fsync);
 
 ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
         /*
          * iomap based filesystems support direct I/O without need for
          * this callback. However, it still needs to be set in
          * inode->a_ops so that open/fcntl know that direct I/O is
          * generally supported.
          */
         return -EINVAL;
 }
 EXPORT_SYMBOL_GPL(noop_direct_IO);
 
 /* Because kfree isn't assignment-compatible with void(void*) ;-/ */
 void kfree_link(void *p)
 {
         kfree(p);
 }
 EXPORT_SYMBOL(kfree_link);
 
 struct inode *alloc_anon_inode(struct super_block *s)
 {
         static const struct address_space_operations anon_aops = {
                 .dirty_folio    = noop_dirty_folio,
         };
         struct inode *inode = new_inode_pseudo(s);
 
         if (!inode)
                 return ERR_PTR(-ENOMEM);
 
         inode->i_ino = get_next_ino();
         inode->i_mapping->a_ops = &anon_aops;
 
         /*
          * Mark the inode dirty from the very beginning,
          * that way it will never be moved to the dirty
          * list because mark_inode_dirty() will think
          * that it already _is_ on the dirty list.
          */
         inode->i_state = I_DIRTY;
         inode->i_mode = S_IRUSR | S_IWUSR;
         inode->i_uid = current_fsuid();
         inode->i_gid = current_fsgid();
         inode->i_flags |= S_PRIVATE;
         simple_inode_init_ts(inode);
         return inode;
 }
 EXPORT_SYMBOL(alloc_anon_inode);
 
 /**
  * simple_nosetlease - generic helper for prohibiting leases
  * @filp: file pointer
  * @arg: type of lease to obtain
  * @flp: new lease supplied for insertion
  * @priv: private data for lm_setup operation
  *
  * Generic helper for filesystems that do not wish to allow leases to be set.
  * All arguments are ignored and it just returns -EINVAL.
  */
 int
 simple_nosetlease(struct file *filp, int arg, struct file_lease **flp,
                   void **priv)
 {
         return -EINVAL;
 }
 EXPORT_SYMBOL(simple_nosetlease);
 
 /**
  * simple_get_link - generic helper to get the target of "fast" symlinks
  * @dentry: not used here
  * @inode: the symlink inode
  * @done: not used here
  *
  * Generic helper for filesystems to use for symlink inodes where a pointer to
  * the symlink target is stored in ->i_link.  NOTE: this isn't normally called,
  * since as an optimization the path lookup code uses any non-NULL ->i_link
  * directly, without calling ->get_link().  But ->get_link() still must be set,
  * to mark the inode_operations as being for a symlink.
  *
  * Return: the symlink target
  */
 const char *simple_get_link(struct dentry *dentry, struct inode *inode,
                             struct delayed_call *done)
 {
         return inode->i_link;
 }
 EXPORT_SYMBOL(simple_get_link);
 
 const struct inode_operations simple_symlink_inode_operations = {
         .get_link = simple_get_link,
 };
 EXPORT_SYMBOL(simple_symlink_inode_operations);
 
 /*
  * Operations for a permanently empty directory.
  */
 static struct dentry *empty_dir_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 {
         return ERR_PTR(-ENOENT);
 }
 
 static int empty_dir_getattr(struct mnt_idmap *idmap,
                              const struct path *path, struct kstat *stat,
                              u32 request_mask, unsigned int query_flags)
 {
         struct inode *inode = d_inode(path->dentry);
         generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
         return 0;
 }
 
 static int empty_dir_setattr(struct mnt_idmap *idmap,
                              struct dentry *dentry, struct iattr *attr)
 {
         return -EPERM;
 }
 
 static ssize_t empty_dir_listxattr(struct dentry *dentry, char *list, size_t size)
 {
         return -EOPNOTSUPP;
 }
 
 static const struct inode_operations empty_dir_inode_operations = {
         .lookup         = empty_dir_lookup,
         .permission     = generic_permission,
         .setattr        = empty_dir_setattr,
         .getattr        = empty_dir_getattr,
         .listxattr      = empty_dir_listxattr,
 };
 
 static loff_t empty_dir_llseek(struct file *file, loff_t offset, int whence)
 {
         /* An empty directory has two entries . and .. at offsets 0 and 1 */
         return generic_file_llseek_size(file, offset, whence, 2, 2);
 }
 
 static int empty_dir_readdir(struct file *file, struct dir_context *ctx)
 {
         dir_emit_dots(file, ctx);
         return 0;
 }
 
 static const struct file_operations empty_dir_operations = {
         .llseek         = empty_dir_llseek,
         .read           = generic_read_dir,
         .iterate_shared = empty_dir_readdir,
         .fsync          = noop_fsync,
 };
 
 
 void make_empty_dir_inode(struct inode *inode)
 {
         set_nlink(inode, 2);
         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO;
         inode->i_uid = GLOBAL_ROOT_UID;
         inode->i_gid = GLOBAL_ROOT_GID;
         inode->i_rdev = 0;
         inode->i_size = 0;
         inode->i_blkbits = PAGE_SHIFT;
         inode->i_blocks = 0;
 
         inode->i_op = &empty_dir_inode_operations;
         inode->i_opflags &= ~IOP_XATTR;
         inode->i_fop = &empty_dir_operations;
 }
 
 bool is_empty_dir_inode(struct inode *inode)
 {
         return (inode->i_fop == &empty_dir_operations) &&
                 (inode->i_op == &empty_dir_inode_operations);
 }
 
 #if IS_ENABLED(CONFIG_UNICODE)
 /**
  * generic_ci_d_compare - generic d_compare implementation for casefolding filesystems
  * @dentry:     dentry whose name we are checking against
  * @len:        len of name of dentry
  * @str:        str pointer to name of dentry
  * @name:       Name to compare against
  *
  * Return: 0 if names match, 1 if mismatch, or -ERRNO
  */
 static int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
                                 const char *str, const struct qstr *name)
 {
         const struct dentry *parent;
         const struct inode *dir;
         char strbuf[DNAME_INLINE_LEN];
         struct qstr qstr;
 
         /*
          * Attempt a case-sensitive match first. It is cheaper and
          * should cover most lookups, including all the sane
          * applications that expect a case-sensitive filesystem.
          *
          * This comparison is safe under RCU because the caller
          * guarantees the consistency between str and len. See
          * __d_lookup_rcu_op_compare() for details.
          */
         if (len == name->len && !memcmp(str, name->name, len))
                 return 0;
 
         parent = READ_ONCE(dentry->d_parent);
         dir = READ_ONCE(parent->d_inode);
         if (!dir || !IS_CASEFOLDED(dir))
                 return 1;
 
         /*
          * If the dentry name is stored in-line, then it may be concurrently
          * modified by a rename.  If this happens, the VFS will eventually retry
          * the lookup, so it doesn't matter what ->d_compare() returns.
          * However, it's unsafe to call utf8_strncasecmp() with an unstable
          * string.  Therefore, we have to copy the name into a temporary buffer.
          */
         if (len <= DNAME_INLINE_LEN - 1) {
                 memcpy(strbuf, str, len);
                 strbuf[len] = 0;
                 str = strbuf;
                 /* prevent compiler from optimizing out the temporary buffer */
                 barrier();
         }
         qstr.len = len;
         qstr.name = str;
 
         return utf8_strncasecmp(dentry->d_sb->s_encoding, name, &qstr);
 }
 
 /**
  * generic_ci_d_hash - generic d_hash implementation for casefolding filesystems
  * @dentry:     dentry of the parent directory
  * @str:        qstr of name whose hash we should fill in
  *
  * Return: 0 if hash was successful or unchanged, and -EINVAL on error
  */
 static int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
 {
         const struct inode *dir = READ_ONCE(dentry->d_inode);
         struct super_block *sb = dentry->d_sb;
         const struct unicode_map *um = sb->s_encoding;
         int ret;
 
         if (!dir || !IS_CASEFOLDED(dir))
                 return 0;
 
         ret = utf8_casefold_hash(um, dentry, str);
         if (ret < 0 && sb_has_strict_encoding(sb))
                 return -EINVAL;
         return 0;
 }
 
 static const struct dentry_operations generic_ci_dentry_ops = {
         .d_hash = generic_ci_d_hash,
         .d_compare = generic_ci_d_compare,
 #ifdef CONFIG_FS_ENCRYPTION
         .d_revalidate = fscrypt_d_revalidate,
 #endif
 };
 
 /**
  * generic_ci_match() - Match a name (case-insensitively) with a dirent.
  * This is a filesystem helper for comparison with directory entries.
  * generic_ci_d_compare should be used in VFS' ->d_compare instead.
  *
  * @parent: Inode of the parent of the dirent under comparison
  * @name: name under lookup.
  * @folded_name: Optional pre-folded name under lookup
  * @de_name: Dirent name.
  * @de_name_len: dirent name length.
  *
  * Test whether a case-insensitive directory entry matches the filename
  * being searched.  If @folded_name is provided, it is used instead of
  * recalculating the casefold of @name.
  *
  * Return: > 0 if the directory entry matches, 0 if it doesn't match, or
  * < 0 on error.
  */
 int generic_ci_match(const struct inode *parent,
                      const struct qstr *name,
                      const struct qstr *folded_name,
                      const u8 *de_name, u32 de_name_len)
 {
         const struct super_block *sb = parent->i_sb;
         const struct unicode_map *um = sb->s_encoding;
         struct fscrypt_str decrypted_name = FSTR_INIT(NULL, de_name_len);
         struct qstr dirent = QSTR_INIT(de_name, de_name_len);
         int res = 0;
 
         if (IS_ENCRYPTED(parent)) {
                 const struct fscrypt_str encrypted_name =
                         FSTR_INIT((u8 *) de_name, de_name_len);
 
                 if (WARN_ON_ONCE(!fscrypt_has_encryption_key(parent)))
                         return -EINVAL;
 
                 decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
                 if (!decrypted_name.name)
                         return -ENOMEM;
                 res = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
                                                 &decrypted_name);
                 if (res < 0) {
                         kfree(decrypted_name.name);
                         return res;
                 }
                 dirent.name = decrypted_name.name;
                 dirent.len = decrypted_name.len;
         }
 
         /*
          * Attempt a case-sensitive match first. It is cheaper and
          * should cover most lookups, including all the sane
          * applications that expect a case-sensitive filesystem.
          */
 
         if (dirent.len == name->len &&
             !memcmp(name->name, dirent.name, dirent.len))
                 goto out;
 
         if (folded_name->name)
                 res = utf8_strncasecmp_folded(um, folded_name, &dirent);
         else
                 res = utf8_strncasecmp(um, name, &dirent);
 
 out:
         kfree(decrypted_name.name);
         if (res < 0 && sb_has_strict_encoding(sb)) {
                 pr_err_ratelimited("Directory contains filename that is invalid UTF-8");
                 return 0;
         }
         return !res;
 }
 EXPORT_SYMBOL(generic_ci_match);
 #endif
 
 #ifdef CONFIG_FS_ENCRYPTION
 static const struct dentry_operations generic_encrypted_dentry_ops = {
         .d_revalidate = fscrypt_d_revalidate,
 };
 #endif
 
 /**
  * generic_set_sb_d_ops - helper for choosing the set of
  * filesystem-wide dentry operations for the enabled features
  * @sb: superblock to be configured
  *
  * Filesystems supporting casefolding and/or fscrypt can call this
  * helper at mount-time to configure sb->s_d_op to best set of dentry
  * operations required for the enabled features. The helper must be
  * called after these have been configured, but before the root dentry
  * is created.
  */
 void generic_set_sb_d_ops(struct super_block *sb)
 {
 #if IS_ENABLED(CONFIG_UNICODE)
         if (sb->s_encoding) {
                 sb->s_d_op = &generic_ci_dentry_ops;
                 return;
         }
 #endif
 #ifdef CONFIG_FS_ENCRYPTION
         if (sb->s_cop) {
                 sb->s_d_op = &generic_encrypted_dentry_ops;
                 return;
         }
 #endif
 }
 EXPORT_SYMBOL(generic_set_sb_d_ops);
 
 /**
  * inode_maybe_inc_iversion - increments i_version
  * @inode: inode with the i_version that should be updated
  * @force: increment the counter even if it's not necessary?
  *
  * Every time the inode is modified, the i_version field must be seen to have
  * changed by any observer.
  *
  * If "force" is set or the QUERIED flag is set, then ensure that we increment
  * the value, and clear the queried flag.
  *
  * In the common case where neither is set, then we can return "false" without
  * updating i_version.
  *
  * If this function returns false, and no other metadata has changed, then we
  * can avoid logging the metadata.
  */
 bool inode_maybe_inc_iversion(struct inode *inode, bool force)
 {
         u64 cur, new;
 
         /*
          * The i_version field is not strictly ordered with any other inode
          * information, but the legacy inode_inc_iversion code used a spinlock
          * to serialize increments.
          *
          * Here, we add full memory barriers to ensure that any de-facto
          * ordering with other info is preserved.
          *
          * This barrier pairs with the barrier in inode_query_iversion()
          */
         smp_mb();
         cur = inode_peek_iversion_raw(inode);
         do {
                 /* If flag is clear then we needn't do anything */
                 if (!force && !(cur & I_VERSION_QUERIED))
                         return false;
 
                 /* Since lowest bit is flag, add 2 to avoid it */
                 new = (cur & ~I_VERSION_QUERIED) + I_VERSION_INCREMENT;
         } while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
         return true;
 }
 EXPORT_SYMBOL(inode_maybe_inc_iversion);
 
 /**
  * inode_query_iversion - read i_version for later use
  * @inode: inode from which i_version should be read
  *
  * Read the inode i_version counter. This should be used by callers that wish
  * to store the returned i_version for later comparison. This will guarantee
  * that a later query of the i_version will result in a different value if
  * anything has changed.
  *
  * In this implementation, we fetch the current value, set the QUERIED flag and
  * then try to swap it into place with a cmpxchg, if it wasn't already set. If
  * that fails, we try again with the newly fetched value from the cmpxchg.
  */
 u64 inode_query_iversion(struct inode *inode)
 {
         u64 cur, new;
 
         cur = inode_peek_iversion_raw(inode);
         do {
                 /* If flag is already set, then no need to swap */
                 if (cur & I_VERSION_QUERIED) {
                         /*
                          * This barrier (and the implicit barrier in the
                          * cmpxchg below) pairs with the barrier in
                          * inode_maybe_inc_iversion().
                          */
                         smp_mb();
                         break;
                 }
 
                 new = cur | I_VERSION_QUERIED;
         } while (!atomic64_try_cmpxchg(&inode->i_version, &cur, new));
         return cur >> I_VERSION_QUERIED_SHIFT;
 }
 EXPORT_SYMBOL(inode_query_iversion);
 
 ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
                 ssize_t direct_written, ssize_t buffered_written)
 {
         struct address_space *mapping = iocb->ki_filp->f_mapping;
         loff_t pos = iocb->ki_pos - buffered_written;
         loff_t end = iocb->ki_pos - 1;
         int err;
 
         /*
          * If the buffered write fallback returned an error, we want to return
          * the number of bytes which were written by direct I/O, or the error
          * code if that was zero.
          *
          * Note that this differs from normal direct-io semantics, which will
          * return -EFOO even if some bytes were written.
          */
         if (unlikely(buffered_written < 0)) {
                 if (direct_written)
                         return direct_written;
                 return buffered_written;
         }
 
         /*
          * We need to ensure that the page cache pages are written to disk and
          * invalidated to preserve the expected O_DIRECT semantics.
          */
         err = filemap_write_and_wait_range(mapping, pos, end);
         if (err < 0) {
                 /*
                  * We don't know how much we wrote, so just return the number of
                  * bytes which were direct-written
                  */
                 iocb->ki_pos -= buffered_written;
                 if (direct_written)
                         return direct_written;
                 return err;
         }
         invalidate_mapping_pages(mapping, pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
         return direct_written + buffered_written;
 }
 EXPORT_SYMBOL_GPL(direct_write_fallback);
 
 /**
  * simple_inode_init_ts - initialize the timestamps for a new inode
  * @inode: inode to be initialized
  *
  * When a new inode is created, most filesystems set the timestamps to the
  * current time. Add a helper to do this.
  */
 struct timespec64 simple_inode_init_ts(struct inode *inode)
 {
         struct timespec64 ts = inode_set_ctime_current(inode);
 
         inode_set_atime_to_ts(inode, ts);
         inode_set_mtime_to_ts(inode, ts);
         return ts;
 }
 EXPORT_SYMBOL(simple_inode_init_ts);
 
 static inline struct dentry *get_stashed_dentry(struct dentry *stashed)
 {
         struct dentry *dentry;
 
         guard(rcu)();
         dentry = READ_ONCE(stashed);
         if (!dentry)
                 return NULL;
         if (!lockref_get_not_dead(&dentry->d_lockref))
                 return NULL;
         return dentry;
 }
 
 static struct dentry *prepare_anon_dentry(struct dentry **stashed,
                                           struct super_block *sb,
                                           void *data)
 {
         struct dentry *dentry;
         struct inode *inode;
         const struct stashed_operations *sops = sb->s_fs_info;
         int ret;
 
         inode = new_inode_pseudo(sb);
         if (!inode) {
                 sops->put_data(data);
                 return ERR_PTR(-ENOMEM);
         }
 
         inode->i_flags |= S_IMMUTABLE;
         inode->i_mode = S_IFREG;
         simple_inode_init_ts(inode);
 
         ret = sops->init_inode(inode, data);
         if (ret < 0) {
                 iput(inode);
                 return ERR_PTR(ret);
         }
 
         /* Notice when this is changed. */
         WARN_ON_ONCE(!S_ISREG(inode->i_mode));
         WARN_ON_ONCE(!IS_IMMUTABLE(inode));
 
         dentry = d_alloc_anon(sb);
         if (!dentry) {
                 iput(inode);
                 return ERR_PTR(-ENOMEM);
         }
 
         /* Store address of location where dentry's supposed to be stashed. */
         dentry->d_fsdata = stashed;
 
         /* @data is now owned by the fs */
         d_instantiate(dentry, inode);
         return dentry;
 }
 
 static struct dentry *stash_dentry(struct dentry **stashed,
                                    struct dentry *dentry)
 {
         guard(rcu)();
         for (;;) {
                 struct dentry *old;
 
                 /* Assume any old dentry was cleared out. */
                 old = cmpxchg(stashed, NULL, dentry);
                 if (likely(!old))
                         return dentry;
 
                 /* Check if somebody else installed a reusable dentry. */
                 if (lockref_get_not_dead(&old->d_lockref))
                         return old;
 
                 /* There's an old dead dentry there, try to take it over. */
                 if (likely(try_cmpxchg(stashed, &old, dentry)))
                         return dentry;
         }
 }
 
 /**
  * path_from_stashed - create path from stashed or new dentry
  * @stashed:    where to retrieve or stash dentry
  * @mnt:        mnt of the filesystems to use
  * @data:       data to store in inode->i_private
  * @path:       path to create
  *
  * The function tries to retrieve a stashed dentry from @stashed. If the dentry
  * is still valid then it will be reused. If the dentry isn't able the function
  * will allocate a new dentry and inode. It will then check again whether it
  * can reuse an existing dentry in case one has been added in the meantime or
  * update @stashed with the newly added dentry.
  *
  * Special-purpose helper for nsfs and pidfs.
  *
  * Return: On success zero and on failure a negative error is returned.
  */
 int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
                       struct path *path)
 {
         struct dentry *dentry;
         const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info;
 
         /* See if dentry can be reused. */
         path->dentry = get_stashed_dentry(*stashed);
         if (path->dentry) {
                 sops->put_data(data);
                 goto out_path;
         }
 
         /* Allocate a new dentry. */
         dentry = prepare_anon_dentry(stashed, mnt->mnt_sb, data);
         if (IS_ERR(dentry))
                 return PTR_ERR(dentry);
 
         /* Added a new dentry. @data is now owned by the filesystem. */
         path->dentry = stash_dentry(stashed, dentry);
         if (path->dentry != dentry)
                 dput(dentry);
 
 out_path:
         WARN_ON_ONCE(path->dentry->d_fsdata != stashed);
         WARN_ON_ONCE(d_inode(path->dentry)->i_private != data);
         path->mnt = mntget(mnt);
         return 0;
 }
 
 void stashed_dentry_prune(struct dentry *dentry)
 {
         struct dentry **stashed = dentry->d_fsdata;
         struct inode *inode = d_inode(dentry);
 
         if (WARN_ON_ONCE(!stashed))
                 return;
 
         if (!inode)
                 return;
 
         /*
          * Only replace our own @dentry as someone else might've
          * already cleared out @dentry and stashed their own
          * dentry in there.
          */
         cmpxchg(stashed, dentry, NULL);
 }
 

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