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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 */
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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>
fb3c8315 17#include <linux/namei.h>
4f41fc59 18#include <linux/seq_file.h>
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19
20#include "kernfs-internal.h"
21
a797bfc3 22struct kmem_cache *kernfs_node_cache;
fa736a95 23
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24static 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
34static 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
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44static 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
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53 seq_dentry(sf, dentry, " \t\n\\");
54 return 0;
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55}
56
f41c5934 57const struct super_operations kernfs_sops = {
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58 .statfs = simple_statfs,
59 .drop_inode = generic_delete_inode,
c637b8ac 60 .evict_inode = kernfs_evict_inode,
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61
62 .remount_fs = kernfs_sop_remount_fs,
63 .show_options = kernfs_sop_show_options,
4f41fc59 64 .show_path = kernfs_sop_show_path,
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65};
66
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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 */
74struct 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
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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 */
89static 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 */
111struct 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);
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138 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
139 strlen(kntmp->name));
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140 dput(dentry);
141 if (IS_ERR(dtmp))
142 return dtmp;
143 knparent = kntmp;
144 dentry = dtmp;
145 } while (true);
146}
147
26fc9cd2 148static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
fa736a95 149{
c525aadd 150 struct kernfs_super_info *info = kernfs_info(sb);
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151 struct inode *inode;
152 struct dentry *root;
153
7d568a83 154 info->sb = sb;
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155 sb->s_blocksize = PAGE_SIZE;
156 sb->s_blocksize_bits = PAGE_SHIFT;
26fc9cd2 157 sb->s_magic = magic;
a797bfc3 158 sb->s_op = &kernfs_sops;
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159 sb->s_time_gran = 1;
160
161 /* get root inode, initialize and unlock it */
a797bfc3 162 mutex_lock(&kernfs_mutex);
c637b8ac 163 inode = kernfs_get_inode(sb, info->root->kn);
a797bfc3 164 mutex_unlock(&kernfs_mutex);
fa736a95 165 if (!inode) {
c637b8ac 166 pr_debug("kernfs: could not get root inode\n");
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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 }
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176 kernfs_get(info->root->kn);
177 root->d_fsdata = info->root->kn;
fa736a95 178 sb->s_root = root;
a797bfc3 179 sb->s_d_op = &kernfs_dops;
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180 return 0;
181}
182
c637b8ac 183static int kernfs_test_super(struct super_block *sb, void *data)
fa736a95 184{
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185 struct kernfs_super_info *sb_info = kernfs_info(sb);
186 struct kernfs_super_info *info = data;
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187
188 return sb_info->root == info->root && sb_info->ns == info->ns;
189}
190
c637b8ac 191static int kernfs_set_super(struct super_block *sb, void *data)
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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 */
206const void *kernfs_super_ns(struct super_block *sb)
207{
c525aadd 208 struct kernfs_super_info *info = kernfs_info(sb);
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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
26fc9cd2 218 * @magic: file system specific magic number
fed95bab 219 * @new_sb_created: tell the caller if we allocated a new superblock
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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 */
229struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
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230 struct kernfs_root *root, unsigned long magic,
231 bool *new_sb_created, const void *ns)
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232{
233 struct super_block *sb;
c525aadd 234 struct kernfs_super_info *info;
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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
c637b8ac 244 sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
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245 if (IS_ERR(sb) || sb->s_fs_info != info)
246 kfree(info);
247 if (IS_ERR(sb))
248 return ERR_CAST(sb);
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249
250 if (new_sb_created)
251 *new_sb_created = !sb->s_root;
252
fa736a95 253 if (!sb->s_root) {
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254 struct kernfs_super_info *info = kernfs_info(sb);
255
26fc9cd2 256 error = kernfs_fill_super(sb, magic);
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257 if (error) {
258 deactivate_locked_super(sb);
259 return ERR_PTR(error);
260 }
261 sb->s_flags |= MS_ACTIVE;
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262
263 mutex_lock(&kernfs_mutex);
264 list_add(&info->node, &root->supers);
265 mutex_unlock(&kernfs_mutex);
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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 */
279void kernfs_kill_sb(struct super_block *sb)
280{
c525aadd 281 struct kernfs_super_info *info = kernfs_info(sb);
324a56e1 282 struct kernfs_node *root_kn = sb->s_root->d_fsdata;
fa736a95 283
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284 mutex_lock(&kernfs_mutex);
285 list_del(&info->node);
286 mutex_unlock(&kernfs_mutex);
287
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288 /*
289 * Remove the superblock from fs_supers/s_instances
c525aadd 290 * so we can't find it, before freeing kernfs_super_info.
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291 */
292 kill_anon_super(sb);
293 kfree(info);
324a56e1 294 kernfs_put(root_kn);
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295}
296
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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 */
309struct 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
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327void __init kernfs_init(void)
328{
a797bfc3 329 kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
324a56e1 330 sizeof(struct kernfs_node),
fa736a95 331 0, SLAB_PANIC, NULL);
fa736a95 332}