1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * kernfs.h - pseudo filesystem decoupled from vfs locking
4 */
5
6 #ifndef __LINUX_KERNFS_H
7 #define __LINUX_KERNFS_H
8
9 #include <linux/err.h>
10 #include <linux/list.h>
11 #include <linux/mutex.h>
12 #include <linux/idr.h>
13 #include <linux/lockdep.h>
14 #include <linux/rbtree.h>
15 #include <linux/atomic.h>
16 #include <linux/bug.h>
17 #include <linux/types.h>
18 #include <linux/uidgid.h>
19 #include <linux/wait.h>
20 #include <linux/rwsem.h>
21 #include <linux/cache.h>
22
23 struct file;
24 struct dentry;
25 struct iattr;
26 struct seq_file;
27 struct vm_area_struct;
28 struct vm_operations_struct;
29 struct super_block;
30 struct file_system_type;
31 struct poll_table_struct;
32 struct fs_context;
33
34 struct kernfs_fs_context;
35 struct kernfs_open_node;
36 struct kernfs_iattrs;
37
38 /*
39 * NR_KERNFS_LOCK_BITS determines size (NR_KERNFS_LOCKS) of hash
40 * table of locks.
41 * Having a small hash table would impact scalability, since
42 * more and more kernfs_node objects will end up using same lock
43 * and having a very large hash table would waste memory.
44 *
45 * At the moment size of hash table of locks is being set based on
46 * the number of CPUs as follows:
47 *
48 * NR_CPU NR_KERNFS_LOCK_BITS NR_KERNFS_LOCKS
49 * 1 1 2
50 * 2-3 2 4
51 * 4-7 4 16
52 * 8-15 6 64
53 * 16-31 8 256
54 * 32 and more 10 1024
55 *
56 * The above relation between NR_CPU and number of locks is based
57 * on some internal experimentation which involved booting qemu
58 * with different values of smp, performing some sysfs operations
59 * on all CPUs and observing how increase in number of locks impacts
60 * completion time of these sysfs operations on each CPU.
61 */
62 #ifdef CONFIG_SMP
63 #define NR_KERNFS_LOCK_BITS (2 * (ilog2(NR_CPUS < 32 ? NR_CPUS : 32)))
64 #else
65 #define NR_KERNFS_LOCK_BITS 1
66 #endif
67
68 #define NR_KERNFS_LOCKS (1 << NR_KERNFS_LOCK_BITS)
69
70 /*
71 * There's one kernfs_open_file for each open file and one kernfs_open_node
72 * for each kernfs_node with one or more open files.
73 *
74 * filp->private_data points to seq_file whose ->private points to
75 * kernfs_open_file.
76 *
77 * kernfs_open_files are chained at kernfs_open_node->files, which is
78 * protected by kernfs_global_locks.open_file_mutex[i].
79 *
80 * To reduce possible contention in sysfs access, arising due to single
81 * locks, use an array of locks (e.g. open_file_mutex) and use kernfs_node
82 * object address as hash keys to get the index of these locks.
83 *
84 * Hashed mutexes are safe to use here because operations using these don't
85 * rely on global exclusion.
86 *
87 * In future we intend to replace other global locks with hashed ones as well.
88 * kernfs_global_locks acts as a holder for all such hash tables.
89 */
90 struct kernfs_global_locks {
91 struct mutex open_file_mutex[NR_KERNFS_LOCKS];
92 };
93
94 enum kernfs_node_type {
95 KERNFS_DIR = 0x0001,
96 KERNFS_FILE = 0x0002,
97 KERNFS_LINK = 0x0004,
98 };
99
100 #define KERNFS_TYPE_MASK 0x000f
101 #define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK
102 #define KERNFS_MAX_USER_XATTRS 128
103 #define KERNFS_USER_XATTR_SIZE_LIMIT (128 << 10)
104
105 enum kernfs_node_flag {
106 KERNFS_ACTIVATED = 0x0010,
107 KERNFS_NS = 0x0020,
108 KERNFS_HAS_SEQ_SHOW = 0x0040,
109 KERNFS_HAS_MMAP = 0x0080,
110 KERNFS_LOCKDEP = 0x0100,
111 KERNFS_HIDDEN = 0x0200,
112 KERNFS_SUICIDAL = 0x0400,
113 KERNFS_SUICIDED = 0x0800,
114 KERNFS_EMPTY_DIR = 0x1000,
115 KERNFS_HAS_RELEASE = 0x2000,
116 KERNFS_REMOVING = 0x4000,
117 };
118
119 /* @flags for kernfs_create_root() */
120 enum kernfs_root_flag {
121 /*
122 * kernfs_nodes are created in the deactivated state and invisible.
123 * They require explicit kernfs_activate() to become visible. This
124 * can be used to make related nodes become visible atomically
125 * after all nodes are created successfully.
126 */
127 KERNFS_ROOT_CREATE_DEACTIVATED = 0x0001,
128
129 /*
130 * For regular files, if the opener has CAP_DAC_OVERRIDE, open(2)
131 * succeeds regardless of the RW permissions. sysfs had an extra
132 * layer of enforcement where open(2) fails with -EACCES regardless
133 * of CAP_DAC_OVERRIDE if the permission doesn't have the
134 * respective read or write access at all (none of S_IRUGO or
135 * S_IWUGO) or the respective operation isn't implemented. The
136 * following flag enables that behavior.
137 */
138 KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK = 0x0002,
139
140 /*
141 * The filesystem supports exportfs operation, so userspace can use
142 * fhandle to access nodes of the fs.
143 */
144 KERNFS_ROOT_SUPPORT_EXPORTOP = 0x0004,
145
146 /*
147 * Support user xattrs to be written to nodes rooted at this root.
148 */
149 KERNFS_ROOT_SUPPORT_USER_XATTR = 0x0008,
150 };
151
152 /* type-specific structures for kernfs_node union members */
153 struct kernfs_elem_dir {
154 unsigned long subdirs;
155 /* children rbtree starts here and goes through kn->rb */
156 struct rb_root children;
157
158 /*
159 * The kernfs hierarchy this directory belongs to. This fits
160 * better directly in kernfs_node but is here to save space.
161 */
162 struct kernfs_root *root;
163 /*
164 * Monotonic revision counter, used to identify if a directory
165 * node has changed during negative dentry revalidation.
166 */
167 unsigned long rev;
168 };
169
170 struct kernfs_elem_symlink {
171 struct kernfs_node *target_kn;
172 };
173
174 struct kernfs_elem_attr {
175 const struct kernfs_ops *ops;
176 struct kernfs_open_node __rcu *open;
177 loff_t size;
178 struct kernfs_node *notify_next; /* for kernfs_notify() */
179 };
180
181 /*
182 * kernfs_node - the building block of kernfs hierarchy. Each and every
183 * kernfs node is represented by single kernfs_node. Most fields are
184 * private to kernfs and shouldn't be accessed directly by kernfs users.
185 *
186 * As long as count reference is held, the kernfs_node itself is
187 * accessible. Dereferencing elem or any other outer entity requires
188 * active reference.
189 */
190 struct kernfs_node {
191 atomic_t count;
192 atomic_t active;
193 #ifdef CONFIG_DEBUG_LOCK_ALLOC
194 struct lockdep_map dep_map;
195 #endif
196 /*
197 * Use kernfs_get_parent() and kernfs_name/path() instead of
198 * accessing the following two fields directly. If the node is
199 * never moved to a different parent, it is safe to access the
200 * parent directly.
201 */
202 struct kernfs_node *parent;
203 const char *name;
204
205 struct rb_node rb;
206
207 const void *ns; /* namespace tag */
208 unsigned int hash; /* ns + name hash */
209 unsigned short flags;
210 umode_t mode;
211
212 union {
213 struct kernfs_elem_dir dir;
214 struct kernfs_elem_symlink symlink;
215 struct kernfs_elem_attr attr;
216 };
217
218 /*
219 * 64bit unique ID. On 64bit ino setups, id is the ino. On 32bit,
220 * the low 32bits are ino and upper generation.
221 */
222 u64 id;
223
224 void *priv;
225 struct kernfs_iattrs *iattr;
226
227 struct rcu_head rcu;
228 };
229
230 /*
231 * kernfs_syscall_ops may be specified on kernfs_create_root() to support
232 * syscalls. These optional callbacks are invoked on the matching syscalls
233 * and can perform any kernfs operations which don't necessarily have to be
234 * the exact operation requested. An active reference is held for each
235 * kernfs_node parameter.
236 */
237 struct kernfs_syscall_ops {
238 int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
239
240 int (*mkdir)(struct kernfs_node *parent, const char *name,
241 umode_t mode);
242 int (*rmdir)(struct kernfs_node *kn);
243 int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
244 const char *new_name);
245 int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
246 struct kernfs_root *root);
247 };
248
249 struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root);
250
251 struct kernfs_open_file {
252 /* published fields */
253 struct kernfs_node *kn;
254 struct file *file;
255 struct seq_file *seq_file;
256 void *priv;
257
258 /* private fields, do not use outside kernfs proper */
259 struct mutex mutex;
260 struct mutex prealloc_mutex;
261 int event;
262 struct list_head list;
263 char *prealloc_buf;
264
265 size_t atomic_write_len;
266 bool mmapped:1;
267 bool released:1;
268 const struct vm_operations_struct *vm_ops;
269 };
270
271 struct kernfs_ops {
272 /*
273 * Optional open/release methods. Both are called with
274 * @of->seq_file populated.
275 */
276 int (*open)(struct kernfs_open_file *of);
277 void (*release)(struct kernfs_open_file *of);
278
279 /*
280 * Read is handled by either seq_file or raw_read().
281 *
282 * If seq_show() is present, seq_file path is active. Other seq
283 * operations are optional and if not implemented, the behavior is
284 * equivalent to single_open(). @sf->private points to the
285 * associated kernfs_open_file.
286 *
287 * read() is bounced through kernel buffer and a read larger than
288 * PAGE_SIZE results in partial operation of PAGE_SIZE.
289 */
290 int (*seq_show)(struct seq_file *sf, void *v);
291
292 void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
293 void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
294 void (*seq_stop)(struct seq_file *sf, void *v);
295
296 ssize_t (*read)(struct kernfs_open_file *of, char *buf, size_t bytes,
297 loff_t off);
298
299 /*
300 * write() is bounced through kernel buffer. If atomic_write_len
301 * is not set, a write larger than PAGE_SIZE results in partial
302 * operations of PAGE_SIZE chunks. If atomic_write_len is set,
303 * writes upto the specified size are executed atomically but
304 * larger ones are rejected with -E2BIG.
305 */
306 size_t atomic_write_len;
307 /*
308 * "prealloc" causes a buffer to be allocated at open for
309 * all read/write requests. As ->seq_show uses seq_read()
310 * which does its own allocation, it is incompatible with
311 * ->prealloc. Provide ->read and ->write with ->prealloc.
312 */
313 bool prealloc;
314 ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
315 loff_t off);
316
317 __poll_t (*poll)(struct kernfs_open_file *of,
318 struct poll_table_struct *pt);
319
320 int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);
321 loff_t (*llseek)(struct kernfs_open_file *of, loff_t offset, int whence);
322 };
323
324 /*
325 * The kernfs superblock creation/mount parameter context.
326 */
327 struct kernfs_fs_context {
328 struct kernfs_root *root; /* Root of the hierarchy being mounted */
329 void *ns_tag; /* Namespace tag of the mount (or NULL) */
330 unsigned long magic; /* File system specific magic number */
331
332 /* The following are set/used by kernfs_mount() */
333 bool new_sb_created; /* Set to T if we allocated a new sb */
334 };
335
336 #ifdef CONFIG_KERNFS
337
338 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
339 {
340 return kn->flags & KERNFS_TYPE_MASK;
341 }
342
343 static inline ino_t kernfs_id_ino(u64 id)
344 {
345 /* id is ino if ino_t is 64bit; otherwise, low 32bits */
346 if (sizeof(ino_t) >= sizeof(u64))
347 return id;
348 else
349 return (u32)id;
350 }
351
352 static inline u32 kernfs_id_gen(u64 id)
353 {
354 /* gen is fixed at 1 if ino_t is 64bit; otherwise, high 32bits */
355 if (sizeof(ino_t) >= sizeof(u64))
356 return 1;
357 else
358 return id >> 32;
359 }
360
361 static inline ino_t kernfs_ino(struct kernfs_node *kn)
362 {
363 return kernfs_id_ino(kn->id);
364 }
365
366 static inline ino_t kernfs_gen(struct kernfs_node *kn)
367 {
368 return kernfs_id_gen(kn->id);
369 }
370
371 /**
372 * kernfs_enable_ns - enable namespace under a directory
373 * @kn: directory of interest, should be empty
374 *
375 * This is to be called right after @kn is created to enable namespace
376 * under it. All children of @kn must have non-NULL namespace tags and
377 * only the ones which match the super_block's tag will be visible.
378 */
379 static inline void kernfs_enable_ns(struct kernfs_node *kn)
380 {
381 WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
382 WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
383 kn->flags |= KERNFS_NS;
384 }
385
386 /**
387 * kernfs_ns_enabled - test whether namespace is enabled
388 * @kn: the node to test
389 *
390 * Test whether namespace filtering is enabled for the children of @ns.
391 */
392 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
393 {
394 return kn->flags & KERNFS_NS;
395 }
396
397 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
398 int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
399 char *buf, size_t buflen);
400 void pr_cont_kernfs_name(struct kernfs_node *kn);
401 void pr_cont_kernfs_path(struct kernfs_node *kn);
402 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
403 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
404 const char *name, const void *ns);
405 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
406 const char *path, const void *ns);
407 void kernfs_get(struct kernfs_node *kn);
408 void kernfs_put(struct kernfs_node *kn);
409
410 struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
411 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
412 struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);
413
414 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
415 struct super_block *sb);
416 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
417 unsigned int flags, void *priv);
418 void kernfs_destroy_root(struct kernfs_root *root);
419
420 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
421 const char *name, umode_t mode,
422 kuid_t uid, kgid_t gid,
423 void *priv, const void *ns);
424 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
425 const char *name);
426 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
427 const char *name, umode_t mode,
428 kuid_t uid, kgid_t gid,
429 loff_t size,
430 const struct kernfs_ops *ops,
431 void *priv, const void *ns,
432 struct lock_class_key *key);
433 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
434 const char *name,
435 struct kernfs_node *target);
436 void kernfs_activate(struct kernfs_node *kn);
437 void kernfs_show(struct kernfs_node *kn, bool show);
438 void kernfs_remove(struct kernfs_node *kn);
439 void kernfs_break_active_protection(struct kernfs_node *kn);
440 void kernfs_unbreak_active_protection(struct kernfs_node *kn);
441 bool kernfs_remove_self(struct kernfs_node *kn);
442 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
443 const void *ns);
444 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
445 const char *new_name, const void *new_ns);
446 int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
447 __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
448 struct poll_table_struct *pt);
449 void kernfs_notify(struct kernfs_node *kn);
450
451 int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
452 void *value, size_t size);
453 int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
454 const void *value, size_t size, int flags);
455
456 const void *kernfs_super_ns(struct super_block *sb);
457 int kernfs_get_tree(struct fs_context *fc);
458 void kernfs_free_fs_context(struct fs_context *fc);
459 void kernfs_kill_sb(struct super_block *sb);
460
461 void kernfs_init(void);
462
463 struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
464 u64 id);
465 #else /* CONFIG_KERNFS */
466
467 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
468 { return 0; } /* whatever */
469
470 static inline void kernfs_enable_ns(struct kernfs_node *kn) { }
471
472 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
473 { return false; }
474
475 static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
476 { return -ENOSYS; }
477
478 static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
479 struct kernfs_node *kn,
480 char *buf, size_t buflen)
481 { return -ENOSYS; }
482
483 static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
484 static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }
485
486 static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
487 { return NULL; }
488
489 static inline struct kernfs_node *
490 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
491 const void *ns)
492 { return NULL; }
493 static inline struct kernfs_node *
494 kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
495 const void *ns)
496 { return NULL; }
497
498 static inline void kernfs_get(struct kernfs_node *kn) { }
499 static inline void kernfs_put(struct kernfs_node *kn) { }
500
501 static inline struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
502 { return NULL; }
503
504 static inline struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
505 { return NULL; }
506
507 static inline struct inode *
508 kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
509 { return NULL; }
510
511 static inline struct kernfs_root *
512 kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
513 void *priv)
514 { return ERR_PTR(-ENOSYS); }
515
516 static inline void kernfs_destroy_root(struct kernfs_root *root) { }
517
518 static inline struct kernfs_node *
519 kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
520 umode_t mode, kuid_t uid, kgid_t gid,
521 void *priv, const void *ns)
522 { return ERR_PTR(-ENOSYS); }
523
524 static inline struct kernfs_node *
525 __kernfs_create_file(struct kernfs_node *parent, const char *name,
526 umode_t mode, kuid_t uid, kgid_t gid,
527 loff_t size, const struct kernfs_ops *ops,
528 void *priv, const void *ns, struct lock_class_key *key)
529 { return ERR_PTR(-ENOSYS); }
530
531 static inline struct kernfs_node *
532 kernfs_create_link(struct kernfs_node *parent, const char *name,
533 struct kernfs_node *target)
534 { return ERR_PTR(-ENOSYS); }
535
536 static inline void kernfs_activate(struct kernfs_node *kn) { }
537
538 static inline void kernfs_remove(struct kernfs_node *kn) { }
539
540 static inline bool kernfs_remove_self(struct kernfs_node *kn)
541 { return false; }
542
543 static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
544 const char *name, const void *ns)
545 { return -ENOSYS; }
546
547 static inline int kernfs_rename_ns(struct kernfs_node *kn,
548 struct kernfs_node *new_parent,
549 const char *new_name, const void *new_ns)
550 { return -ENOSYS; }
551
552 static inline int kernfs_setattr(struct kernfs_node *kn,
553 const struct iattr *iattr)
554 { return -ENOSYS; }
555
556 static inline __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
557 struct poll_table_struct *pt)
558 { return -ENOSYS; }
559
560 static inline void kernfs_notify(struct kernfs_node *kn) { }
561
562 static inline int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
563 void *value, size_t size)
564 { return -ENOSYS; }
565
566 static inline int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
567 const void *value, size_t size, int flags)
568 { return -ENOSYS; }
569
570 static inline const void *kernfs_super_ns(struct super_block *sb)
571 { return NULL; }
572
573 static inline int kernfs_get_tree(struct fs_context *fc)
574 { return -ENOSYS; }
575
576 static inline void kernfs_free_fs_context(struct fs_context *fc) { }
577
578 static inline void kernfs_kill_sb(struct super_block *sb) { }
579
580 static inline void kernfs_init(void) { }
581
582 #endif /* CONFIG_KERNFS */
583
584 /**
585 * kernfs_path - build full path of a given node
586 * @kn: kernfs_node of interest
587 * @buf: buffer to copy @kn's name into
588 * @buflen: size of @buf
589 *
590 * If @kn is NULL result will be "(null)".
591 *
592 * Returns the length of the full path. If the full length is equal to or
593 * greater than @buflen, @buf contains the truncated path with the trailing
594 * '\0'. On error, -errno is returned.
595 */
596 static inline int kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
597 {
598 return kernfs_path_from_node(kn, NULL, buf, buflen);
599 }
600
601 static inline struct kernfs_node *
602 kernfs_find_and_get(struct kernfs_node *kn, const char *name)
603 {
604 return kernfs_find_and_get_ns(kn, name, NULL);
605 }
606
607 static inline struct kernfs_node *
608 kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
609 {
610 return kernfs_walk_and_get_ns(kn, path, NULL);
611 }
612
613 static inline struct kernfs_node *
614 kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
615 void *priv)
616 {
617 return kernfs_create_dir_ns(parent, name, mode,
618 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
619 priv, NULL);
620 }
621
622 static inline int kernfs_remove_by_name(struct kernfs_node *parent,
623 const char *name)
624 {
625 return kernfs_remove_by_name_ns(parent, name, NULL);
626 }
627
628 static inline int kernfs_rename(struct kernfs_node *kn,
629 struct kernfs_node *new_parent,
630 const char *new_name)
631 {
632 return kernfs_rename_ns(kn, new_parent, new_name, NULL);
633 }
634
635 #endif /* __LINUX_KERNFS_H */
636
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