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
23struct file;
24struct dentry;
25struct iattr;
26struct seq_file;
27struct vm_area_struct;
28struct vm_operations_struct;
29struct super_block;
30struct file_system_type;
31struct poll_table_struct;
32struct fs_context;
33
34struct kernfs_fs_context;
35struct kernfs_open_node;
36struct 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 */
90struct kernfs_global_locks {
91 struct mutex open_file_mutex[NR_KERNFS_LOCKS];
92};
93
94enum 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
105enum 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() */
120enum 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 */
153struct 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
170struct kernfs_elem_symlink {
171 struct kernfs_node *target_kn;
172};
173
174struct 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 */
190struct 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 union {
210 struct kernfs_elem_dir dir;
211 struct kernfs_elem_symlink symlink;
212 struct kernfs_elem_attr attr;
213 };
214
215 void *priv;
216
217 /*
218 * 64bit unique ID. On 64bit ino setups, id is the ino. On 32bit,
219 * the low 32bits are ino and upper generation.
220 */
221 u64 id;
222
223 unsigned short flags;
224 umode_t mode;
225 struct kernfs_iattrs *iattr;
226};
227
228/*
229 * kernfs_syscall_ops may be specified on kernfs_create_root() to support
230 * syscalls. These optional callbacks are invoked on the matching syscalls
231 * and can perform any kernfs operations which don't necessarily have to be
232 * the exact operation requested. An active reference is held for each
233 * kernfs_node parameter.
234 */
235struct kernfs_syscall_ops {
236 int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
237
238 int (*mkdir)(struct kernfs_node *parent, const char *name,
239 umode_t mode);
240 int (*rmdir)(struct kernfs_node *kn);
241 int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
242 const char *new_name);
243 int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
244 struct kernfs_root *root);
245};
246
247struct kernfs_node *kernfs_root_to_node(struct kernfs_root *root);
248
249struct kernfs_open_file {
250 /* published fields */
251 struct kernfs_node *kn;
252 struct file *file;
253 struct seq_file *seq_file;
254 void *priv;
255
256 /* private fields, do not use outside kernfs proper */
257 struct mutex mutex;
258 struct mutex prealloc_mutex;
259 int event;
260 struct list_head list;
261 char *prealloc_buf;
262
263 size_t atomic_write_len;
264 bool mmapped:1;
265 bool released:1;
266 const struct vm_operations_struct *vm_ops;
267};
268
269struct kernfs_ops {
270 /*
271 * Optional open/release methods. Both are called with
272 * @of->seq_file populated.
273 */
274 int (*open)(struct kernfs_open_file *of);
275 void (*release)(struct kernfs_open_file *of);
276
277 /*
278 * Read is handled by either seq_file or raw_read().
279 *
280 * If seq_show() is present, seq_file path is active. Other seq
281 * operations are optional and if not implemented, the behavior is
282 * equivalent to single_open(). @sf->private points to the
283 * associated kernfs_open_file.
284 *
285 * read() is bounced through kernel buffer and a read larger than
286 * PAGE_SIZE results in partial operation of PAGE_SIZE.
287 */
288 int (*seq_show)(struct seq_file *sf, void *v);
289
290 void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
291 void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
292 void (*seq_stop)(struct seq_file *sf, void *v);
293
294 ssize_t (*read)(struct kernfs_open_file *of, char *buf, size_t bytes,
295 loff_t off);
296
297 /*
298 * write() is bounced through kernel buffer. If atomic_write_len
299 * is not set, a write larger than PAGE_SIZE results in partial
300 * operations of PAGE_SIZE chunks. If atomic_write_len is set,
301 * writes upto the specified size are executed atomically but
302 * larger ones are rejected with -E2BIG.
303 */
304 size_t atomic_write_len;
305 /*
306 * "prealloc" causes a buffer to be allocated at open for
307 * all read/write requests. As ->seq_show uses seq_read()
308 * which does its own allocation, it is incompatible with
309 * ->prealloc. Provide ->read and ->write with ->prealloc.
310 */
311 bool prealloc;
312 ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
313 loff_t off);
314
315 __poll_t (*poll)(struct kernfs_open_file *of,
316 struct poll_table_struct *pt);
317
318 int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);
319 loff_t (*llseek)(struct kernfs_open_file *of, loff_t offset, int whence);
320};
321
322/*
323 * The kernfs superblock creation/mount parameter context.
324 */
325struct kernfs_fs_context {
326 struct kernfs_root *root; /* Root of the hierarchy being mounted */
327 void *ns_tag; /* Namespace tag of the mount (or NULL) */
328 unsigned long magic; /* File system specific magic number */
329
330 /* The following are set/used by kernfs_mount() */
331 bool new_sb_created; /* Set to T if we allocated a new sb */
332};
333
334#ifdef CONFIG_KERNFS
335
336static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
337{
338 return kn->flags & KERNFS_TYPE_MASK;
339}
340
341static inline ino_t kernfs_id_ino(u64 id)
342{
343 /* id is ino if ino_t is 64bit; otherwise, low 32bits */
344 if (sizeof(ino_t) >= sizeof(u64))
345 return id;
346 else
347 return (u32)id;
348}
349
350static inline u32 kernfs_id_gen(u64 id)
351{
352 /* gen is fixed at 1 if ino_t is 64bit; otherwise, high 32bits */
353 if (sizeof(ino_t) >= sizeof(u64))
354 return 1;
355 else
356 return id >> 32;
357}
358
359static inline ino_t kernfs_ino(struct kernfs_node *kn)
360{
361 return kernfs_id_ino(id: kn->id);
362}
363
364static inline ino_t kernfs_gen(struct kernfs_node *kn)
365{
366 return kernfs_id_gen(id: kn->id);
367}
368
369/**
370 * kernfs_enable_ns - enable namespace under a directory
371 * @kn: directory of interest, should be empty
372 *
373 * This is to be called right after @kn is created to enable namespace
374 * under it. All children of @kn must have non-NULL namespace tags and
375 * only the ones which match the super_block's tag will be visible.
376 */
377static inline void kernfs_enable_ns(struct kernfs_node *kn)
378{
379 WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
380 WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
381 kn->flags |= KERNFS_NS;
382}
383
384/**
385 * kernfs_ns_enabled - test whether namespace is enabled
386 * @kn: the node to test
387 *
388 * Test whether namespace filtering is enabled for the children of @ns.
389 */
390static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
391{
392 return kn->flags & KERNFS_NS;
393}
394
395int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
396int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
397 char *buf, size_t buflen);
398void pr_cont_kernfs_name(struct kernfs_node *kn);
399void pr_cont_kernfs_path(struct kernfs_node *kn);
400struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
401struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
402 const char *name, const void *ns);
403struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
404 const char *path, const void *ns);
405void kernfs_get(struct kernfs_node *kn);
406void kernfs_put(struct kernfs_node *kn);
407
408struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
409struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
410struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);
411
412struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
413 struct super_block *sb);
414struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
415 unsigned int flags, void *priv);
416void kernfs_destroy_root(struct kernfs_root *root);
417
418struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
419 const char *name, umode_t mode,
420 kuid_t uid, kgid_t gid,
421 void *priv, const void *ns);
422struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
423 const char *name);
424struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
425 const char *name, umode_t mode,
426 kuid_t uid, kgid_t gid,
427 loff_t size,
428 const struct kernfs_ops *ops,
429 void *priv, const void *ns,
430 struct lock_class_key *key);
431struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
432 const char *name,
433 struct kernfs_node *target);
434void kernfs_activate(struct kernfs_node *kn);
435void kernfs_show(struct kernfs_node *kn, bool show);
436void kernfs_remove(struct kernfs_node *kn);
437void kernfs_break_active_protection(struct kernfs_node *kn);
438void kernfs_unbreak_active_protection(struct kernfs_node *kn);
439bool kernfs_remove_self(struct kernfs_node *kn);
440int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
441 const void *ns);
442int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
443 const char *new_name, const void *new_ns);
444int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
445__poll_t kernfs_generic_poll(struct kernfs_open_file *of,
446 struct poll_table_struct *pt);
447void kernfs_notify(struct kernfs_node *kn);
448
449int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
450 void *value, size_t size);
451int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
452 const void *value, size_t size, int flags);
453
454const void *kernfs_super_ns(struct super_block *sb);
455int kernfs_get_tree(struct fs_context *fc);
456void kernfs_free_fs_context(struct fs_context *fc);
457void kernfs_kill_sb(struct super_block *sb);
458
459void kernfs_init(void);
460
461struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
462 u64 id);
463#else /* CONFIG_KERNFS */
464
465static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
466{ return 0; } /* whatever */
467
468static inline void kernfs_enable_ns(struct kernfs_node *kn) { }
469
470static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
471{ return false; }
472
473static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
474{ return -ENOSYS; }
475
476static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
477 struct kernfs_node *kn,
478 char *buf, size_t buflen)
479{ return -ENOSYS; }
480
481static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
482static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }
483
484static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
485{ return NULL; }
486
487static inline struct kernfs_node *
488kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
489 const void *ns)
490{ return NULL; }
491static inline struct kernfs_node *
492kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
493 const void *ns)
494{ return NULL; }
495
496static inline void kernfs_get(struct kernfs_node *kn) { }
497static inline void kernfs_put(struct kernfs_node *kn) { }
498
499static inline struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
500{ return NULL; }
501
502static inline struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
503{ return NULL; }
504
505static inline struct inode *
506kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
507{ return NULL; }
508
509static inline struct kernfs_root *
510kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
511 void *priv)
512{ return ERR_PTR(-ENOSYS); }
513
514static inline void kernfs_destroy_root(struct kernfs_root *root) { }
515
516static inline struct kernfs_node *
517kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
518 umode_t mode, kuid_t uid, kgid_t gid,
519 void *priv, const void *ns)
520{ return ERR_PTR(-ENOSYS); }
521
522static inline struct kernfs_node *
523__kernfs_create_file(struct kernfs_node *parent, const char *name,
524 umode_t mode, kuid_t uid, kgid_t gid,
525 loff_t size, const struct kernfs_ops *ops,
526 void *priv, const void *ns, struct lock_class_key *key)
527{ return ERR_PTR(-ENOSYS); }
528
529static inline struct kernfs_node *
530kernfs_create_link(struct kernfs_node *parent, const char *name,
531 struct kernfs_node *target)
532{ return ERR_PTR(-ENOSYS); }
533
534static inline void kernfs_activate(struct kernfs_node *kn) { }
535
536static inline void kernfs_remove(struct kernfs_node *kn) { }
537
538static inline bool kernfs_remove_self(struct kernfs_node *kn)
539{ return false; }
540
541static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
542 const char *name, const void *ns)
543{ return -ENOSYS; }
544
545static inline int kernfs_rename_ns(struct kernfs_node *kn,
546 struct kernfs_node *new_parent,
547 const char *new_name, const void *new_ns)
548{ return -ENOSYS; }
549
550static inline int kernfs_setattr(struct kernfs_node *kn,
551 const struct iattr *iattr)
552{ return -ENOSYS; }
553
554static inline __poll_t kernfs_generic_poll(struct kernfs_open_file *of,
555 struct poll_table_struct *pt)
556{ return -ENOSYS; }
557
558static inline void kernfs_notify(struct kernfs_node *kn) { }
559
560static inline int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
561 void *value, size_t size)
562{ return -ENOSYS; }
563
564static inline int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
565 const void *value, size_t size, int flags)
566{ return -ENOSYS; }
567
568static inline const void *kernfs_super_ns(struct super_block *sb)
569{ return NULL; }
570
571static inline int kernfs_get_tree(struct fs_context *fc)
572{ return -ENOSYS; }
573
574static inline void kernfs_free_fs_context(struct fs_context *fc) { }
575
576static inline void kernfs_kill_sb(struct super_block *sb) { }
577
578static inline void kernfs_init(void) { }
579
580#endif /* CONFIG_KERNFS */
581
582/**
583 * kernfs_path - build full path of a given node
584 * @kn: kernfs_node of interest
585 * @buf: buffer to copy @kn's name into
586 * @buflen: size of @buf
587 *
588 * If @kn is NULL result will be "(null)".
589 *
590 * Returns the length of the full path. If the full length is equal to or
591 * greater than @buflen, @buf contains the truncated path with the trailing
592 * '\0'. On error, -errno is returned.
593 */
594static inline int kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
595{
596 return kernfs_path_from_node(root_kn: kn, NULL, buf, buflen);
597}
598
599static inline struct kernfs_node *
600kernfs_find_and_get(struct kernfs_node *kn, const char *name)
601{
602 return kernfs_find_and_get_ns(parent: kn, name, NULL);
603}
604
605static inline struct kernfs_node *
606kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
607{
608 return kernfs_walk_and_get_ns(parent: kn, path, NULL);
609}
610
611static inline struct kernfs_node *
612kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
613 void *priv)
614{
615 return kernfs_create_dir_ns(parent, name, mode,
616 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
617 priv, NULL);
618}
619
620static inline int kernfs_remove_by_name(struct kernfs_node *parent,
621 const char *name)
622{
623 return kernfs_remove_by_name_ns(parent, name, NULL);
624}
625
626static inline int kernfs_rename(struct kernfs_node *kn,
627 struct kernfs_node *new_parent,
628 const char *new_name)
629{
630 return kernfs_rename_ns(kn, new_parent, new_name, NULL);
631}
632
633#endif /* __LINUX_KERNFS_H */
634

source code of linux/include/linux/kernfs.h