summaryrefslogtreecommitdiffstats
path: root/fs/kernfs/mount.c
blob: b3d73ad52b22ae9d22f2cea762fa0d5d34809e3e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
/*
 * fs/kernfs/mount.c - kernfs mount implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/seq_file.h>

#include "kernfs-internal.h"

struct kmem_cache *kernfs_node_cache;

static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
{
	struct kernfs_root *root = kernfs_info(sb)->root;
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->remount_fs)
		return scops->remount_fs(root, flags, data);
	return 0;
}

static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
{
	struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_options)
		return scops->show_options(sf, root);
	return 0;
}

static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
{
	struct kernfs_node *node = dentry->d_fsdata;
	struct kernfs_root *root = kernfs_root(node);
	struct kernfs_syscall_ops *scops = root->syscall_ops;

	if (scops && scops->show_path)
		return scops->show_path(sf, node, root);

	seq_dentry(sf, dentry, " \t\n\\");
	return 0;
}

const struct super_operations kernfs_sops = {
	.statfs		= simple_statfs,
	.drop_inode	= generic_delete_inode,
	.evict_inode	= kernfs_evict_inode,

	.remount_fs	= kernfs_sop_remount_fs,
	.show_options	= kernfs_sop_show_options,
	.show_path	= kernfs_sop_show_path,
};

/**
 * kernfs_root_from_sb - determine kernfs_root associated with a super_block
 * @sb: the super_block in question
 *
 * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
 * %NULL is returned.
 */
struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
{
	if (sb->s_op == &kernfs_sops)
		return kernfs_info(sb)->root;
	return NULL;
}

/*
 * find the next ancestor in the path down to @child, where @parent was the
 * ancestor whose descendant we want to find.
 *
 * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
 * node.  If @parent is b, then we return the node for c.
 * Passing in d as @parent is not ok.
 */
static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
					      struct kernfs_node *parent)
{
	if (child == parent) {
		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
		return NULL;
	}

	while (child->parent != parent) {
		if (!child->parent)
			return NULL;
		child = child->parent;
	}

	return child;
}

/**
 * kernfs_node_dentry - get a dentry for the given kernfs_node
 * @kn: kernfs_node for which a dentry is needed
 * @sb: the kernfs super_block
 */
struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
				  struct super_block *sb)
{
	struct dentry *dentry;
	struct kernfs_node *knparent = NULL;

	BUG_ON(sb->s_op != &kernfs_sops);

	dentry = dget(sb->s_root);

	/* Check if this is the root kernfs_node */
	if (!kn->parent)
		return dentry;

	knparent = find_next_ancestor(kn, NULL);
	if (WARN_ON(!knparent))
		return ERR_PTR(-EINVAL);

	do {
		struct dentry *dtmp;
		struct kernfs_node *kntmp;

		if (kn == knparent)
			return dentry;
		kntmp = find_next_ancestor(kn, knparent);
		if (WARN_ON(!kntmp))
			return ERR_PTR(-EINVAL);
		dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
					       strlen(kntmp->name));
		dput(dentry);
		if (IS_ERR(dtmp))
			return dtmp;
		knparent = kntmp;
		dentry = dtmp;
	} while (true);
}

static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct inode *inode;
	struct dentry *root;

	info->sb = sb;
	/* Userspace would break if executables or devices appear on sysfs */
	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
	sb->s_blocksize = PAGE_SIZE;
	sb->s_blocksize_bits = PAGE_SHIFT;
	sb->s_magic = magic;
	sb->s_op = &kernfs_sops;
	sb->s_time_gran = 1;

	/* get root inode, initialize and unlock it */
	mutex_lock(&kernfs_mutex);
	inode = kernfs_get_inode(sb, info->root->kn);
	mutex_unlock(&kernfs_mutex);
	if (!inode) {
		pr_debug("kernfs: could not get root inode\n");
		return -ENOMEM;
	}

	/* instantiate and link root dentry */
	root = d_make_root(inode);
	if (!root) {
		pr_debug("%s: could not get root dentry!\n", __func__);
		return -ENOMEM;
	}
	kernfs_get(info->root->kn);
	root->d_fsdata = info->root->kn;
	sb->s_root = root;
	sb->s_d_op = &kernfs_dops;
	return 0;
}

static int kernfs_test_super(struct super_block *sb, void *data)
{
	struct kernfs_super_info *sb_info = kernfs_info(sb);
	struct kernfs_super_info *info = data;

	return sb_info->root == info->root && sb_info->ns == info->ns;
}

static int kernfs_set_super(struct super_block *sb, void *data)
{
	int error;
	error = set_anon_super(sb, data);
	if (!error)
		sb->s_fs_info = data;
	return error;
}

/**
 * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 * @sb: super_block of interest
 *
 * Return the namespace tag associated with kernfs super_block @sb.
 */
const void *kernfs_super_ns(struct super_block *sb)
{
	struct kernfs_super_info *info = kernfs_info(sb);

	return info->ns;
}

/**
 * kernfs_mount_ns - kernfs mount helper
 * @fs_type: file_system_type of the fs being mounted
 * @flags: mount flags specified for the mount
 * @root: kernfs_root of the hierarchy being mounted
 * @magic: file system specific magic number
 * @new_sb_created: tell the caller if we allocated a new superblock
 * @ns: optional namespace tag of the mount
 *
 * This is to be called from each kernfs user's file_system_type->mount()
 * implementation, which should pass through the specified @fs_type and
 * @flags, and specify the hierarchy and namespace tag to mount via @root
 * and @ns, respectively.
 *
 * The return value can be passed to the vfs layer verbatim.
 */
struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
				struct kernfs_root *root, unsigned long magic,
				bool *new_sb_created, const void *ns)
{
	struct super_block *sb;
	struct kernfs_super_info *info;
	int error;

	info = kzalloc(sizeof(*info), GFP_KERNEL);
	if (!info)
		return ERR_PTR(-ENOMEM);

	info->root = root;
	info->ns = ns;

	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
			 &init_user_ns, info);
	if (IS_ERR(sb) || sb->s_fs_info != info)
		kfree(info);
	if (IS_ERR(sb))
		return ERR_CAST(sb);

	if (new_sb_created)
		*new_sb_created = !sb->s_root;

	if (!sb->s_root) {
		struct kernfs_super_info *info = kernfs_info(sb);

		error = kernfs_fill_super(sb, magic);
		if (error) {
			deactivate_locked_super(sb);
			return ERR_PTR(error);
		}
		sb->s_flags |= MS_ACTIVE;

		mutex_lock(&kernfs_mutex);
		list_add(&info->node, &root->supers);
		mutex_unlock(&kernfs_mutex);
	}

	return dget(sb->s_root);
}

/**
 * kernfs_kill_sb - kill_sb for kernfs
 * @sb: super_block being killed
 *
 * This can be used directly for file_system_type->kill_sb().  If a kernfs
 * user needs extra cleanup, it can implement its own kill_sb() and call
 * this function at the end.
 */
void kernfs_kill_sb(struct super_block *sb)
{
	struct kernfs_super_info *info = kernfs_info(sb);
	struct kernfs_node *root_kn = sb->s_root->d_fsdata;

	mutex_lock(&kernfs_mutex);
	list_del(&info->node);
	mutex_unlock(&kernfs_mutex);

	/*
	 * Remove the superblock from fs_supers/s_instances
	 * so we can't find it, before freeing kernfs_super_info.
	 */
	kill_anon_super(sb);
	kfree(info);
	kernfs_put(root_kn);
}

/**
 * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 * @kernfs_root: the kernfs_root in question
 * @ns: the namespace tag
 *
 * Pin the superblock so the superblock won't be destroyed in subsequent
 * operations.  This can be used to block ->kill_sb() which may be useful
 * for kernfs users which dynamically manage superblocks.
 *
 * Returns NULL if there's no superblock associated to this kernfs_root, or
 * -EINVAL if the superblock is being freed.
 */
struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
{
	struct kernfs_super_info *info;
	struct super_block *sb = NULL;

	mutex_lock(&kernfs_mutex);
	list_for_each_entry(info, &root->supers, node) {
		if (info->ns == ns) {
			sb = info->sb;
			if (!atomic_inc_not_zero(&info->sb->s_active))
				sb = ERR_PTR(-EINVAL);
			break;
		}
	}
	mutex_unlock(&kernfs_mutex);
	return sb;
}

void __init kernfs_init(void)
{
	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
					      sizeof(struct kernfs_node),
					      0, SLAB_PANIC, NULL);
}
OpenPOWER on IntegriCloud