1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/kernfs/mount.c - kernfs mount implementation
4 *
5 * Copyright (c) 2001-3 Patrick Mochel
6 * Copyright (c) 2007 SUSE Linux Products GmbH
7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
8 */
9
10#include <linux/fs.h>
11#include <linux/mount.h>
12#include <linux/init.h>
13#include <linux/magic.h>
14#include <linux/slab.h>
15#include <linux/pagemap.h>
16#include <linux/namei.h>
17#include <linux/seq_file.h>
18#include <linux/exportfs.h>
19#include <linux/uuid.h>
20#include <linux/statfs.h>
21
22#include "kernfs-internal.h"
23
24struct kmem_cache *kernfs_node_cache __ro_after_init;
25struct kmem_cache *kernfs_iattrs_cache __ro_after_init;
26struct kernfs_global_locks *kernfs_locks __ro_after_init;
27
28static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
29{
30 struct kernfs_root *root = kernfs_root(kn: kernfs_dentry_node(dentry));
31 struct kernfs_syscall_ops *scops = root->syscall_ops;
32
33 if (scops && scops->show_options)
34 return scops->show_options(sf, root);
35 return 0;
36}
37
38static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
39{
40 struct kernfs_node *node = kernfs_dentry_node(dentry);
41 struct kernfs_root *root = kernfs_root(kn: node);
42 struct kernfs_syscall_ops *scops = root->syscall_ops;
43
44 if (scops && scops->show_path)
45 return scops->show_path(sf, node, root);
46
47 seq_dentry(sf, dentry, " \t\n\\");
48 return 0;
49}
50
51static int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
52{
53 simple_statfs(dentry, buf);
54 buf->f_fsid = uuid_to_fsid(uuid: dentry->d_sb->s_uuid.b);
55 return 0;
56}
57
58const struct super_operations kernfs_sops = {
59 .statfs = kernfs_statfs,
60 .drop_inode = generic_delete_inode,
61 .evict_inode = kernfs_evict_inode,
62
63 .show_options = kernfs_sop_show_options,
64 .show_path = kernfs_sop_show_path,
65};
66
67static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
68 struct inode *parent)
69{
70 struct kernfs_node *kn = inode->i_private;
71
72 if (*max_len < 2) {
73 *max_len = 2;
74 return FILEID_INVALID;
75 }
76
77 *max_len = 2;
78 *(u64 *)fh = kn->id;
79 return FILEID_KERNFS;
80}
81
82static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
83 struct fid *fid, int fh_len,
84 int fh_type, bool get_parent)
85{
86 struct kernfs_super_info *info = kernfs_info(sb);
87 struct kernfs_node *kn;
88 struct inode *inode;
89 u64 id;
90
91 if (fh_len < 2)
92 return NULL;
93
94 switch (fh_type) {
95 case FILEID_KERNFS:
96 id = *(u64 *)fid;
97 break;
98 case FILEID_INO32_GEN:
99 case FILEID_INO32_GEN_PARENT:
100 /*
101 * blk_log_action() exposes "LOW32,HIGH32" pair without
102 * type and userland can call us with generic fid
103 * constructed from them. Combine it back to ID. See
104 * blk_log_action().
105 */
106 id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
107 break;
108 default:
109 return NULL;
110 }
111
112 kn = kernfs_find_and_get_node_by_id(root: info->root, id);
113 if (!kn)
114 return ERR_PTR(error: -ESTALE);
115
116 if (get_parent) {
117 struct kernfs_node *parent;
118
119 parent = kernfs_get_parent(kn);
120 kernfs_put(kn);
121 kn = parent;
122 if (!kn)
123 return ERR_PTR(error: -ESTALE);
124 }
125
126 inode = kernfs_get_inode(sb, kn);
127 kernfs_put(kn);
128 if (!inode)
129 return ERR_PTR(error: -ESTALE);
130
131 return d_obtain_alias(inode);
132}
133
134static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
135 struct fid *fid, int fh_len,
136 int fh_type)
137{
138 return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, get_parent: false);
139}
140
141static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
142 struct fid *fid, int fh_len,
143 int fh_type)
144{
145 return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, get_parent: true);
146}
147
148static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
149{
150 struct kernfs_node *kn = kernfs_dentry_node(dentry: child);
151
152 return d_obtain_alias(kernfs_get_inode(sb: child->d_sb, kn: kn->parent));
153}
154
155static const struct export_operations kernfs_export_ops = {
156 .encode_fh = kernfs_encode_fh,
157 .fh_to_dentry = kernfs_fh_to_dentry,
158 .fh_to_parent = kernfs_fh_to_parent,
159 .get_parent = kernfs_get_parent_dentry,
160};
161
162/**
163 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
164 * @sb: the super_block in question
165 *
166 * Return: the kernfs_root associated with @sb. If @sb is not a kernfs one,
167 * %NULL is returned.
168 */
169struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
170{
171 if (sb->s_op == &kernfs_sops)
172 return kernfs_info(sb)->root;
173 return NULL;
174}
175
176/*
177 * find the next ancestor in the path down to @child, where @parent was the
178 * ancestor whose descendant we want to find.
179 *
180 * Say the path is /a/b/c/d. @child is d, @parent is %NULL. We return the root
181 * node. If @parent is b, then we return the node for c.
182 * Passing in d as @parent is not ok.
183 */
184static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
185 struct kernfs_node *parent)
186{
187 if (child == parent) {
188 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
189 return NULL;
190 }
191
192 while (child->parent != parent) {
193 if (!child->parent)
194 return NULL;
195 child = child->parent;
196 }
197
198 return child;
199}
200
201/**
202 * kernfs_node_dentry - get a dentry for the given kernfs_node
203 * @kn: kernfs_node for which a dentry is needed
204 * @sb: the kernfs super_block
205 *
206 * Return: the dentry pointer
207 */
208struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
209 struct super_block *sb)
210{
211 struct dentry *dentry;
212 struct kernfs_node *knparent = NULL;
213
214 BUG_ON(sb->s_op != &kernfs_sops);
215
216 dentry = dget(dentry: sb->s_root);
217
218 /* Check if this is the root kernfs_node */
219 if (!kn->parent)
220 return dentry;
221
222 knparent = find_next_ancestor(child: kn, NULL);
223 if (WARN_ON(!knparent)) {
224 dput(dentry);
225 return ERR_PTR(error: -EINVAL);
226 }
227
228 do {
229 struct dentry *dtmp;
230 struct kernfs_node *kntmp;
231
232 if (kn == knparent)
233 return dentry;
234 kntmp = find_next_ancestor(child: kn, parent: knparent);
235 if (WARN_ON(!kntmp)) {
236 dput(dentry);
237 return ERR_PTR(error: -EINVAL);
238 }
239 dtmp = lookup_positive_unlocked(kntmp->name, dentry,
240 strlen(kntmp->name));
241 dput(dentry);
242 if (IS_ERR(ptr: dtmp))
243 return dtmp;
244 knparent = kntmp;
245 dentry = dtmp;
246 } while (true);
247}
248
249static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
250{
251 struct kernfs_super_info *info = kernfs_info(sb);
252 struct kernfs_root *kf_root = kfc->root;
253 struct inode *inode;
254 struct dentry *root;
255
256 info->sb = sb;
257 /* Userspace would break if executables or devices appear on sysfs */
258 sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
259 sb->s_blocksize = PAGE_SIZE;
260 sb->s_blocksize_bits = PAGE_SHIFT;
261 sb->s_magic = kfc->magic;
262 sb->s_op = &kernfs_sops;
263 sb->s_xattr = kernfs_xattr_handlers;
264 if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
265 sb->s_export_op = &kernfs_export_ops;
266 sb->s_time_gran = 1;
267
268 /* sysfs dentries and inodes don't require IO to create */
269 sb->s_shrink->seeks = 0;
270
271 /* get root inode, initialize and unlock it */
272 down_read(sem: &kf_root->kernfs_rwsem);
273 inode = kernfs_get_inode(sb, kn: info->root->kn);
274 up_read(sem: &kf_root->kernfs_rwsem);
275 if (!inode) {
276 pr_debug("kernfs: could not get root inode\n");
277 return -ENOMEM;
278 }
279
280 /* instantiate and link root dentry */
281 root = d_make_root(inode);
282 if (!root) {
283 pr_debug("%s: could not get root dentry!\n", __func__);
284 return -ENOMEM;
285 }
286 sb->s_root = root;
287 sb->s_d_op = &kernfs_dops;
288 return 0;
289}
290
291static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
292{
293 struct kernfs_super_info *sb_info = kernfs_info(sb);
294 struct kernfs_super_info *info = fc->s_fs_info;
295
296 return sb_info->root == info->root && sb_info->ns == info->ns;
297}
298
299static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
300{
301 struct kernfs_fs_context *kfc = fc->fs_private;
302
303 kfc->ns_tag = NULL;
304 return set_anon_super_fc(s: sb, fc);
305}
306
307/**
308 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
309 * @sb: super_block of interest
310 *
311 * Return: the namespace tag associated with kernfs super_block @sb.
312 */
313const void *kernfs_super_ns(struct super_block *sb)
314{
315 struct kernfs_super_info *info = kernfs_info(sb);
316
317 return info->ns;
318}
319
320/**
321 * kernfs_get_tree - kernfs filesystem access/retrieval helper
322 * @fc: The filesystem context.
323 *
324 * This is to be called from each kernfs user's fs_context->ops->get_tree()
325 * implementation, which should set the specified ->@fs_type and ->@flags, and
326 * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
327 * respectively.
328 *
329 * Return: %0 on success, -errno on failure.
330 */
331int kernfs_get_tree(struct fs_context *fc)
332{
333 struct kernfs_fs_context *kfc = fc->fs_private;
334 struct super_block *sb;
335 struct kernfs_super_info *info;
336 int error;
337
338 info = kzalloc(size: sizeof(*info), GFP_KERNEL);
339 if (!info)
340 return -ENOMEM;
341
342 info->root = kfc->root;
343 info->ns = kfc->ns_tag;
344 INIT_LIST_HEAD(list: &info->node);
345
346 fc->s_fs_info = info;
347 sb = sget_fc(fc, test: kernfs_test_super, set: kernfs_set_super);
348 if (IS_ERR(ptr: sb))
349 return PTR_ERR(ptr: sb);
350
351 if (!sb->s_root) {
352 struct kernfs_super_info *info = kernfs_info(sb);
353 struct kernfs_root *root = kfc->root;
354
355 kfc->new_sb_created = true;
356
357 error = kernfs_fill_super(sb, kfc);
358 if (error) {
359 deactivate_locked_super(sb);
360 return error;
361 }
362 sb->s_flags |= SB_ACTIVE;
363
364 uuid_gen(u: &sb->s_uuid);
365
366 down_write(sem: &root->kernfs_supers_rwsem);
367 list_add(new: &info->node, head: &info->root->supers);
368 up_write(sem: &root->kernfs_supers_rwsem);
369 }
370
371 fc->root = dget(dentry: sb->s_root);
372 return 0;
373}
374
375void kernfs_free_fs_context(struct fs_context *fc)
376{
377 /* Note that we don't deal with kfc->ns_tag here. */
378 kfree(objp: fc->s_fs_info);
379 fc->s_fs_info = NULL;
380}
381
382/**
383 * kernfs_kill_sb - kill_sb for kernfs
384 * @sb: super_block being killed
385 *
386 * This can be used directly for file_system_type->kill_sb(). If a kernfs
387 * user needs extra cleanup, it can implement its own kill_sb() and call
388 * this function at the end.
389 */
390void kernfs_kill_sb(struct super_block *sb)
391{
392 struct kernfs_super_info *info = kernfs_info(sb);
393 struct kernfs_root *root = info->root;
394
395 down_write(sem: &root->kernfs_supers_rwsem);
396 list_del(entry: &info->node);
397 up_write(sem: &root->kernfs_supers_rwsem);
398
399 /*
400 * Remove the superblock from fs_supers/s_instances
401 * so we can't find it, before freeing kernfs_super_info.
402 */
403 kill_anon_super(sb);
404 kfree(objp: info);
405}
406
407static void __init kernfs_mutex_init(void)
408{
409 int count;
410
411 for (count = 0; count < NR_KERNFS_LOCKS; count++)
412 mutex_init(&kernfs_locks->open_file_mutex[count]);
413}
414
415static void __init kernfs_lock_init(void)
416{
417 kernfs_locks = kmalloc(size: sizeof(struct kernfs_global_locks), GFP_KERNEL);
418 WARN_ON(!kernfs_locks);
419
420 kernfs_mutex_init();
421}
422
423void __init kernfs_init(void)
424{
425 kernfs_node_cache = kmem_cache_create(name: "kernfs_node_cache",
426 size: sizeof(struct kernfs_node),
427 align: 0, SLAB_PANIC, NULL);
428
429 /* Creates slab cache for kernfs inode attributes */
430 kernfs_iattrs_cache = kmem_cache_create(name: "kernfs_iattrs_cache",
431 size: sizeof(struct kernfs_iattrs),
432 align: 0, SLAB_PANIC, NULL);
433
434 kernfs_lock_init();
435}
436

source code of linux/fs/kernfs/mount.c