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Linux/fs/kernfs/mount.c

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

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