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Tejun Heob8441ed2013-11-24 09:54:58 -05001/*
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 */
Tejun Heofa736a92013-11-28 14:54:44 -050010
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>
Aditya Kalifb3c8312016-01-29 02:54:08 -060017#include <linux/namei.h>
Serge E. Hallyn4f41fc52016-05-09 09:59:55 -050018#include <linux/seq_file.h>
Tejun Heofa736a92013-11-28 14:54:44 -050019
20#include "kernfs-internal.h"
21
Tejun Heoa797bfc2013-12-11 14:11:57 -050022struct kmem_cache *kernfs_node_cache;
Tejun Heofa736a92013-11-28 14:54:44 -050023
Tejun Heo6a7fed42014-02-03 14:09:10 -050024static 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
Serge E. Hallyn4f41fc52016-05-09 09:59:55 -050044static 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
Serge E. Hallyn3cc9b232016-05-12 00:29:45 -050053 seq_dentry(sf, dentry, " \t\n\\");
54 return 0;
Serge E. Hallyn4f41fc52016-05-09 09:59:55 -050055}
56
Li Zefanf41c5932014-02-14 16:57:27 +080057const struct super_operations kernfs_sops = {
Tejun Heofa736a92013-11-28 14:54:44 -050058 .statfs = simple_statfs,
59 .drop_inode = generic_delete_inode,
Tejun Heoc637b8a2013-12-11 14:11:58 -050060 .evict_inode = kernfs_evict_inode,
Tejun Heo6a7fed42014-02-03 14:09:10 -050061
62 .remount_fs = kernfs_sop_remount_fs,
63 .show_options = kernfs_sop_show_options,
Serge E. Hallyn4f41fc52016-05-09 09:59:55 -050064 .show_path = kernfs_sop_show_path,
Tejun Heofa736a92013-11-28 14:54:44 -050065};
66
Tejun Heo0c23b222014-02-03 14:09:15 -050067/**
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
Aditya Kalifb3c8312016-01-29 02:54:08 -060081/*
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);
Al Viro779b8392016-04-11 08:42:55 -0400138 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
139 strlen(kntmp->name));
Aditya Kalifb3c8312016-01-29 02:54:08 -0600140 dput(dentry);
141 if (IS_ERR(dtmp))
142 return dtmp;
143 knparent = kntmp;
144 dentry = dtmp;
145 } while (true);
146}
147
Jianyu Zhan26fc9cd2014-04-26 15:40:28 +0800148static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
Tejun Heofa736a92013-11-28 14:54:44 -0500149{
Tejun Heoc525aad2013-12-11 14:11:55 -0500150 struct kernfs_super_info *info = kernfs_info(sb);
Tejun Heofa736a92013-11-28 14:54:44 -0500151 struct inode *inode;
152 struct dentry *root;
153
Tejun Heo7d568a82014-04-09 11:07:30 -0400154 info->sb = sb;
Eric W. Biedermana2982cc2016-06-09 15:34:02 -0500155 /* Userspace would break if executables or devices appear on sysfs */
156 sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
Kirill A. Shutemov09cbfea2016-04-01 15:29:47 +0300157 sb->s_blocksize = PAGE_SIZE;
158 sb->s_blocksize_bits = PAGE_SHIFT;
Jianyu Zhan26fc9cd2014-04-26 15:40:28 +0800159 sb->s_magic = magic;
Tejun Heoa797bfc2013-12-11 14:11:57 -0500160 sb->s_op = &kernfs_sops;
Tejun Heofa736a92013-11-28 14:54:44 -0500161 sb->s_time_gran = 1;
162
163 /* get root inode, initialize and unlock it */
Tejun Heoa797bfc2013-12-11 14:11:57 -0500164 mutex_lock(&kernfs_mutex);
Tejun Heoc637b8a2013-12-11 14:11:58 -0500165 inode = kernfs_get_inode(sb, info->root->kn);
Tejun Heoa797bfc2013-12-11 14:11:57 -0500166 mutex_unlock(&kernfs_mutex);
Tejun Heofa736a92013-11-28 14:54:44 -0500167 if (!inode) {
Tejun Heoc637b8a2013-12-11 14:11:58 -0500168 pr_debug("kernfs: could not get root inode\n");
Tejun Heofa736a92013-11-28 14:54:44 -0500169 return -ENOMEM;
170 }
171
172 /* instantiate and link root dentry */
173 root = d_make_root(inode);
174 if (!root) {
175 pr_debug("%s: could not get root dentry!\n", __func__);
176 return -ENOMEM;
177 }
Tejun Heo324a56e2013-12-11 14:11:53 -0500178 kernfs_get(info->root->kn);
179 root->d_fsdata = info->root->kn;
Tejun Heofa736a92013-11-28 14:54:44 -0500180 sb->s_root = root;
Tejun Heoa797bfc2013-12-11 14:11:57 -0500181 sb->s_d_op = &kernfs_dops;
Tejun Heofa736a92013-11-28 14:54:44 -0500182 return 0;
183}
184
Tejun Heoc637b8a2013-12-11 14:11:58 -0500185static int kernfs_test_super(struct super_block *sb, void *data)
Tejun Heofa736a92013-11-28 14:54:44 -0500186{
Tejun Heoc525aad2013-12-11 14:11:55 -0500187 struct kernfs_super_info *sb_info = kernfs_info(sb);
188 struct kernfs_super_info *info = data;
Tejun Heofa736a92013-11-28 14:54:44 -0500189
190 return sb_info->root == info->root && sb_info->ns == info->ns;
191}
192
Tejun Heoc637b8a2013-12-11 14:11:58 -0500193static int kernfs_set_super(struct super_block *sb, void *data)
Tejun Heofa736a92013-11-28 14:54:44 -0500194{
195 int error;
196 error = set_anon_super(sb, data);
197 if (!error)
198 sb->s_fs_info = data;
199 return error;
200}
201
202/**
203 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
204 * @sb: super_block of interest
205 *
206 * Return the namespace tag associated with kernfs super_block @sb.
207 */
208const void *kernfs_super_ns(struct super_block *sb)
209{
Tejun Heoc525aad2013-12-11 14:11:55 -0500210 struct kernfs_super_info *info = kernfs_info(sb);
Tejun Heofa736a92013-11-28 14:54:44 -0500211
212 return info->ns;
213}
214
215/**
216 * kernfs_mount_ns - kernfs mount helper
217 * @fs_type: file_system_type of the fs being mounted
218 * @flags: mount flags specified for the mount
219 * @root: kernfs_root of the hierarchy being mounted
Jianyu Zhan26fc9cd2014-04-26 15:40:28 +0800220 * @magic: file system specific magic number
Li Zefanfed95ba2014-02-25 19:28:44 +0800221 * @new_sb_created: tell the caller if we allocated a new superblock
Tejun Heofa736a92013-11-28 14:54:44 -0500222 * @ns: optional namespace tag of the mount
223 *
224 * This is to be called from each kernfs user's file_system_type->mount()
225 * implementation, which should pass through the specified @fs_type and
226 * @flags, and specify the hierarchy and namespace tag to mount via @root
227 * and @ns, respectively.
228 *
229 * The return value can be passed to the vfs layer verbatim.
230 */
231struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
Jianyu Zhan26fc9cd2014-04-26 15:40:28 +0800232 struct kernfs_root *root, unsigned long magic,
233 bool *new_sb_created, const void *ns)
Tejun Heofa736a92013-11-28 14:54:44 -0500234{
235 struct super_block *sb;
Tejun Heoc525aad2013-12-11 14:11:55 -0500236 struct kernfs_super_info *info;
Tejun Heofa736a92013-11-28 14:54:44 -0500237 int error;
238
239 info = kzalloc(sizeof(*info), GFP_KERNEL);
240 if (!info)
241 return ERR_PTR(-ENOMEM);
242
243 info->root = root;
244 info->ns = ns;
245
Eric W. Biederman6e4eab52016-05-24 09:29:01 -0500246 sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
247 &init_user_ns, info);
Tejun Heofa736a92013-11-28 14:54:44 -0500248 if (IS_ERR(sb) || sb->s_fs_info != info)
249 kfree(info);
250 if (IS_ERR(sb))
251 return ERR_CAST(sb);
Li Zefanfed95ba2014-02-25 19:28:44 +0800252
253 if (new_sb_created)
254 *new_sb_created = !sb->s_root;
255
Tejun Heofa736a92013-11-28 14:54:44 -0500256 if (!sb->s_root) {
Tejun Heo7d568a82014-04-09 11:07:30 -0400257 struct kernfs_super_info *info = kernfs_info(sb);
258
Jianyu Zhan26fc9cd2014-04-26 15:40:28 +0800259 error = kernfs_fill_super(sb, magic);
Tejun Heofa736a92013-11-28 14:54:44 -0500260 if (error) {
261 deactivate_locked_super(sb);
262 return ERR_PTR(error);
263 }
264 sb->s_flags |= MS_ACTIVE;
Tejun Heo7d568a82014-04-09 11:07:30 -0400265
266 mutex_lock(&kernfs_mutex);
267 list_add(&info->node, &root->supers);
268 mutex_unlock(&kernfs_mutex);
Tejun Heofa736a92013-11-28 14:54:44 -0500269 }
270
271 return dget(sb->s_root);
272}
273
274/**
275 * kernfs_kill_sb - kill_sb for kernfs
276 * @sb: super_block being killed
277 *
278 * This can be used directly for file_system_type->kill_sb(). If a kernfs
279 * user needs extra cleanup, it can implement its own kill_sb() and call
280 * this function at the end.
281 */
282void kernfs_kill_sb(struct super_block *sb)
283{
Tejun Heoc525aad2013-12-11 14:11:55 -0500284 struct kernfs_super_info *info = kernfs_info(sb);
Tejun Heo324a56e2013-12-11 14:11:53 -0500285 struct kernfs_node *root_kn = sb->s_root->d_fsdata;
Tejun Heofa736a92013-11-28 14:54:44 -0500286
Tejun Heo7d568a82014-04-09 11:07:30 -0400287 mutex_lock(&kernfs_mutex);
288 list_del(&info->node);
289 mutex_unlock(&kernfs_mutex);
290
Tejun Heofa736a92013-11-28 14:54:44 -0500291 /*
292 * Remove the superblock from fs_supers/s_instances
Tejun Heoc525aad2013-12-11 14:11:55 -0500293 * so we can't find it, before freeing kernfs_super_info.
Tejun Heofa736a92013-11-28 14:54:44 -0500294 */
295 kill_anon_super(sb);
296 kfree(info);
Tejun Heo324a56e2013-12-11 14:11:53 -0500297 kernfs_put(root_kn);
Tejun Heofa736a92013-11-28 14:54:44 -0500298}
299
Li Zefan4e264452014-06-30 11:50:28 +0800300/**
301 * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
302 * @kernfs_root: the kernfs_root in question
303 * @ns: the namespace tag
304 *
305 * Pin the superblock so the superblock won't be destroyed in subsequent
306 * operations. This can be used to block ->kill_sb() which may be useful
307 * for kernfs users which dynamically manage superblocks.
308 *
309 * Returns NULL if there's no superblock associated to this kernfs_root, or
310 * -EINVAL if the superblock is being freed.
311 */
312struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
313{
314 struct kernfs_super_info *info;
315 struct super_block *sb = NULL;
316
317 mutex_lock(&kernfs_mutex);
318 list_for_each_entry(info, &root->supers, node) {
319 if (info->ns == ns) {
320 sb = info->sb;
321 if (!atomic_inc_not_zero(&info->sb->s_active))
322 sb = ERR_PTR(-EINVAL);
323 break;
324 }
325 }
326 mutex_unlock(&kernfs_mutex);
327 return sb;
328}
329
Tejun Heofa736a92013-11-28 14:54:44 -0500330void __init kernfs_init(void)
331{
Tejun Heoa797bfc2013-12-11 14:11:57 -0500332 kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
Tejun Heo324a56e2013-12-11 14:11:53 -0500333 sizeof(struct kernfs_node),
Tejun Heofa736a92013-11-28 14:54:44 -0500334 0, SLAB_PANIC, NULL);
Tejun Heofa736a92013-11-28 14:54:44 -0500335}