xref: /linux/fs/kernfs/mount.c (revision 2bc46b3ad3c15165f91459b07ff8682478683194)
1 /*
2  * fs/kernfs/mount.c - kernfs mount implementation
3  *
4  * Copyright (c) 2001-3 Patrick Mochel
5  * Copyright (c) 2007 SUSE Linux Products GmbH
6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
7  *
8  * This file is released under the GPLv2.
9  */
10 
11 #include <linux/fs.h>
12 #include <linux/mount.h>
13 #include <linux/init.h>
14 #include <linux/magic.h>
15 #include <linux/slab.h>
16 #include <linux/pagemap.h>
17 #include <linux/namei.h>
18 #include <linux/seq_file.h>
19 
20 #include "kernfs-internal.h"
21 
22 struct kmem_cache *kernfs_node_cache;
23 
24 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
25 {
26 	struct kernfs_root *root = kernfs_info(sb)->root;
27 	struct kernfs_syscall_ops *scops = root->syscall_ops;
28 
29 	if (scops && scops->remount_fs)
30 		return scops->remount_fs(root, flags, data);
31 	return 0;
32 }
33 
34 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
35 {
36 	struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
37 	struct kernfs_syscall_ops *scops = root->syscall_ops;
38 
39 	if (scops && scops->show_options)
40 		return scops->show_options(sf, root);
41 	return 0;
42 }
43 
44 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
45 {
46 	struct kernfs_node *node = dentry->d_fsdata;
47 	struct kernfs_root *root = kernfs_root(node);
48 	struct kernfs_syscall_ops *scops = root->syscall_ops;
49 
50 	if (scops && scops->show_path)
51 		return scops->show_path(sf, node, root);
52 
53 	seq_dentry(sf, dentry, " \t\n\\");
54 	return 0;
55 }
56 
57 const struct super_operations kernfs_sops = {
58 	.statfs		= simple_statfs,
59 	.drop_inode	= generic_delete_inode,
60 	.evict_inode	= kernfs_evict_inode,
61 
62 	.remount_fs	= kernfs_sop_remount_fs,
63 	.show_options	= kernfs_sop_show_options,
64 	.show_path	= kernfs_sop_show_path,
65 };
66 
67 /**
68  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
69  * @sb: the super_block in question
70  *
71  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
72  * %NULL is returned.
73  */
74 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
75 {
76 	if (sb->s_op == &kernfs_sops)
77 		return kernfs_info(sb)->root;
78 	return NULL;
79 }
80 
81 /*
82  * find the next ancestor in the path down to @child, where @parent was the
83  * ancestor whose descendant we want to find.
84  *
85  * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
86  * node.  If @parent is b, then we return the node for c.
87  * Passing in d as @parent is not ok.
88  */
89 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
90 					      struct kernfs_node *parent)
91 {
92 	if (child == parent) {
93 		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
94 		return NULL;
95 	}
96 
97 	while (child->parent != parent) {
98 		if (!child->parent)
99 			return NULL;
100 		child = child->parent;
101 	}
102 
103 	return child;
104 }
105 
106 /**
107  * kernfs_node_dentry - get a dentry for the given kernfs_node
108  * @kn: kernfs_node for which a dentry is needed
109  * @sb: the kernfs super_block
110  */
111 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
112 				  struct super_block *sb)
113 {
114 	struct dentry *dentry;
115 	struct kernfs_node *knparent = NULL;
116 
117 	BUG_ON(sb->s_op != &kernfs_sops);
118 
119 	dentry = dget(sb->s_root);
120 
121 	/* Check if this is the root kernfs_node */
122 	if (!kn->parent)
123 		return dentry;
124 
125 	knparent = find_next_ancestor(kn, NULL);
126 	if (WARN_ON(!knparent))
127 		return ERR_PTR(-EINVAL);
128 
129 	do {
130 		struct dentry *dtmp;
131 		struct kernfs_node *kntmp;
132 
133 		if (kn == knparent)
134 			return dentry;
135 		kntmp = find_next_ancestor(kn, knparent);
136 		if (WARN_ON(!kntmp))
137 			return ERR_PTR(-EINVAL);
138 		dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
139 					       strlen(kntmp->name));
140 		dput(dentry);
141 		if (IS_ERR(dtmp))
142 			return dtmp;
143 		knparent = kntmp;
144 		dentry = dtmp;
145 	} while (true);
146 }
147 
148 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
149 {
150 	struct kernfs_super_info *info = kernfs_info(sb);
151 	struct inode *inode;
152 	struct dentry *root;
153 
154 	info->sb = sb;
155 	sb->s_blocksize = PAGE_SIZE;
156 	sb->s_blocksize_bits = PAGE_SHIFT;
157 	sb->s_magic = magic;
158 	sb->s_op = &kernfs_sops;
159 	sb->s_time_gran = 1;
160 
161 	/* get root inode, initialize and unlock it */
162 	mutex_lock(&kernfs_mutex);
163 	inode = kernfs_get_inode(sb, info->root->kn);
164 	mutex_unlock(&kernfs_mutex);
165 	if (!inode) {
166 		pr_debug("kernfs: could not get root inode\n");
167 		return -ENOMEM;
168 	}
169 
170 	/* instantiate and link root dentry */
171 	root = d_make_root(inode);
172 	if (!root) {
173 		pr_debug("%s: could not get root dentry!\n", __func__);
174 		return -ENOMEM;
175 	}
176 	kernfs_get(info->root->kn);
177 	root->d_fsdata = info->root->kn;
178 	sb->s_root = root;
179 	sb->s_d_op = &kernfs_dops;
180 	return 0;
181 }
182 
183 static int kernfs_test_super(struct super_block *sb, void *data)
184 {
185 	struct kernfs_super_info *sb_info = kernfs_info(sb);
186 	struct kernfs_super_info *info = data;
187 
188 	return sb_info->root == info->root && sb_info->ns == info->ns;
189 }
190 
191 static int kernfs_set_super(struct super_block *sb, void *data)
192 {
193 	int error;
194 	error = set_anon_super(sb, data);
195 	if (!error)
196 		sb->s_fs_info = data;
197 	return error;
198 }
199 
200 /**
201  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
202  * @sb: super_block of interest
203  *
204  * Return the namespace tag associated with kernfs super_block @sb.
205  */
206 const void *kernfs_super_ns(struct super_block *sb)
207 {
208 	struct kernfs_super_info *info = kernfs_info(sb);
209 
210 	return info->ns;
211 }
212 
213 /**
214  * kernfs_mount_ns - kernfs mount helper
215  * @fs_type: file_system_type of the fs being mounted
216  * @flags: mount flags specified for the mount
217  * @root: kernfs_root of the hierarchy being mounted
218  * @magic: file system specific magic number
219  * @new_sb_created: tell the caller if we allocated a new superblock
220  * @ns: optional namespace tag of the mount
221  *
222  * This is to be called from each kernfs user's file_system_type->mount()
223  * implementation, which should pass through the specified @fs_type and
224  * @flags, and specify the hierarchy and namespace tag to mount via @root
225  * and @ns, respectively.
226  *
227  * The return value can be passed to the vfs layer verbatim.
228  */
229 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
230 				struct kernfs_root *root, unsigned long magic,
231 				bool *new_sb_created, const void *ns)
232 {
233 	struct super_block *sb;
234 	struct kernfs_super_info *info;
235 	int error;
236 
237 	info = kzalloc(sizeof(*info), GFP_KERNEL);
238 	if (!info)
239 		return ERR_PTR(-ENOMEM);
240 
241 	info->root = root;
242 	info->ns = ns;
243 
244 	sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
245 	if (IS_ERR(sb) || sb->s_fs_info != info)
246 		kfree(info);
247 	if (IS_ERR(sb))
248 		return ERR_CAST(sb);
249 
250 	if (new_sb_created)
251 		*new_sb_created = !sb->s_root;
252 
253 	if (!sb->s_root) {
254 		struct kernfs_super_info *info = kernfs_info(sb);
255 
256 		error = kernfs_fill_super(sb, magic);
257 		if (error) {
258 			deactivate_locked_super(sb);
259 			return ERR_PTR(error);
260 		}
261 		sb->s_flags |= MS_ACTIVE;
262 
263 		mutex_lock(&kernfs_mutex);
264 		list_add(&info->node, &root->supers);
265 		mutex_unlock(&kernfs_mutex);
266 	}
267 
268 	return dget(sb->s_root);
269 }
270 
271 /**
272  * kernfs_kill_sb - kill_sb for kernfs
273  * @sb: super_block being killed
274  *
275  * This can be used directly for file_system_type->kill_sb().  If a kernfs
276  * user needs extra cleanup, it can implement its own kill_sb() and call
277  * this function at the end.
278  */
279 void kernfs_kill_sb(struct super_block *sb)
280 {
281 	struct kernfs_super_info *info = kernfs_info(sb);
282 	struct kernfs_node *root_kn = sb->s_root->d_fsdata;
283 
284 	mutex_lock(&kernfs_mutex);
285 	list_del(&info->node);
286 	mutex_unlock(&kernfs_mutex);
287 
288 	/*
289 	 * Remove the superblock from fs_supers/s_instances
290 	 * so we can't find it, before freeing kernfs_super_info.
291 	 */
292 	kill_anon_super(sb);
293 	kfree(info);
294 	kernfs_put(root_kn);
295 }
296 
297 /**
298  * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
299  * @kernfs_root: the kernfs_root in question
300  * @ns: the namespace tag
301  *
302  * Pin the superblock so the superblock won't be destroyed in subsequent
303  * operations.  This can be used to block ->kill_sb() which may be useful
304  * for kernfs users which dynamically manage superblocks.
305  *
306  * Returns NULL if there's no superblock associated to this kernfs_root, or
307  * -EINVAL if the superblock is being freed.
308  */
309 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
310 {
311 	struct kernfs_super_info *info;
312 	struct super_block *sb = NULL;
313 
314 	mutex_lock(&kernfs_mutex);
315 	list_for_each_entry(info, &root->supers, node) {
316 		if (info->ns == ns) {
317 			sb = info->sb;
318 			if (!atomic_inc_not_zero(&info->sb->s_active))
319 				sb = ERR_PTR(-EINVAL);
320 			break;
321 		}
322 	}
323 	mutex_unlock(&kernfs_mutex);
324 	return sb;
325 }
326 
327 void __init kernfs_init(void)
328 {
329 	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
330 					      sizeof(struct kernfs_node),
331 					      0, SLAB_PANIC, NULL);
332 }
333