aboutsummaryrefslogtreecommitdiffstats
path: root/fs/anon_inodes.c
blob: 47a65df8c87142e60600d69391f1d25c357b52a5 (plain) (blame)
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
/*
 *  fs/anon_inodes.c
 *
 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
 *
 *  Thanks to Arnd Bergmann for code review and suggestions.
 *  More changes for Thomas Gleixner suggestions.
 *
 */

#include <linux/cred.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/magic.h>
#include <linux/anon_inodes.h>

#include <asm/uaccess.h>

static struct vfsmount *anon_inode_mnt __read_mostly;
static struct inode *anon_inode_inode;
static const struct file_operations anon_inode_fops;

/*
 * anon_inodefs_dname() is called from d_path().
 */
static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
	return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
				dentry->d_name.name);
}

static const struct dentry_operations anon_inodefs_dentry_operations = {
	.d_dname	= anon_inodefs_dname,
};

/*
 * nop .set_page_dirty method so that people can use .page_mkwrite on
 * anon inodes.
 */
static int anon_set_page_dirty(struct page *page)
{
	return 0;
};

static const struct address_space_operations anon_aops = {
	.set_page_dirty = anon_set_page_dirty,
};

/*
 * A single inode exists for all anon_inode files. Contrary to pipes,
 * anon_inode inodes have no associated per-instance data, so we need
 * only allocate one of them.
 */
static struct inode *anon_inode_mkinode(struct super_block *s)
{
	struct inode *inode = new_inode_pseudo(s);

	if (!inode)
		return ERR_PTR(-ENOMEM);

	inode->i_ino = get_next_ino();
	inode->i_fop = &anon_inode_fops;

	inode->i_mapping->a_ops = &anon_aops;

	/*
	 * Mark the inode dirty from the very beginning,
	 * that way it will never be moved to the dirty
	 * list because mark_inode_dirty() will think
	 * that it already _is_ on the dirty list.
	 */
	inode->i_state = I_DIRTY;
	inode->i_mode = S_IRUSR | S_IWUSR;
	inode->i_uid = current_fsuid();
	inode->i_gid = current_fsgid();
	inode->i_flags |= S_PRIVATE;
	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
	return inode;
}

static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
				int flags, const char *dev_name, void *data)
{
	struct dentry *root;
	root = mount_pseudo(fs_type, "anon_inode:", NULL,
			&anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
	if (!IS_ERR(root)) {
		struct super_block *s = root->d_sb;
		anon_inode_inode = anon_inode_mkinode(s);
		if (IS_ERR(anon_inode_inode)) {
			dput(root);
			deactivate_locked_super(s);
			root = ERR_CAST(anon_inode_inode);
		}
	}
	return root;
}

static struct file_system_type anon_inode_fs_type = {
	.name		= "anon_inodefs",
	.mount		= anon_inodefs_mount,
	.kill_sb	= kill_anon_super,
};

/**
 * anon_inode_getfile - creates a new file instance by hooking it up to an
 *                      anonymous inode, and a dentry that describe the "class"
 *                      of the file
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 *
 * Creates a new file by hooking it on a single inode. This is useful for files
 * that do not need to have a full-fledged inode in order to operate correctly.
 * All the files created with anon_inode_getfile() will share a single inode,
 * hence saving memory and avoiding code duplication for the file/inode/dentry
 * setup.  Returns the newly created file* or an error pointer.
 */
struct file *anon_inode_getfile(const char *name,
				const struct file_operations *fops,
				void *priv, int flags)
{
	struct qstr this;
	struct path path;
	struct file *file;

	if (IS_ERR(anon_inode_inode))
		return ERR_PTR(-ENODEV);

	if (fops->owner && !try_module_get(fops->owner))
		return ERR_PTR(-ENOENT);

	/*
	 * Link the inode to a directory entry by creating a unique name
	 * using the inode sequence number.
	 */
	file = ERR_PTR(-ENOMEM);
	this.name = name;
	this.len = strlen(name);
	this.hash = 0;
	path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
	if (!path.dentry)
		goto err_module;

	path.mnt = mntget(anon_inode_mnt);
	/*
	 * We know the anon_inode inode count is always greater than zero,
	 * so ihold() is safe.
	 */
	ihold(anon_inode_inode);

	d_instantiate(path.dentry, anon_inode_inode);

	file = alloc_file(&path, OPEN_FMODE(flags), fops);
	if (IS_ERR(file))
		goto err_dput;
	file->f_mapping = anon_inode_inode->i_mapping;

	file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
	file->private_data = priv;

	return file;

err_dput:
	path_put(&path);
err_module:
	module_put(fops->owner);
	return file;
}
EXPORT_SYMBOL_GPL(anon_inode_getfile);

/**
 * anon_inode_getfd - creates a new file instance by hooking it up to an
 *                    anonymous inode, and a dentry that describe the "class"
 *                    of the file
 *
 * @name:    [in]    name of the "class" of the new file
 * @fops:    [in]    file operations for the new file
 * @priv:    [in]    private data for the new file (will be file's private_data)
 * @flags:   [in]    flags
 *
 * Creates a new file by hooking it on a single inode. This is useful for files
 * that do not need to have a full-fledged inode in order to operate correctly.
 * All the files created with anon_inode_getfd() will share a single inode,
 * hence saving memory and avoiding code duplication for the file/inode/dentry
 * setup.  Returns new descriptor or an error code.
 */
int anon_inode_getfd(const char *name, const struct file_operations *fops,
		     void *priv, int flags)
{
	int error, fd;
	struct file *file;

	error = get_unused_fd_flags(flags);
	if (error < 0)
		return error;
	fd = error;

	file = anon_inode_getfile(name, fops, priv, flags);
	if (IS_ERR(file)) {
		error = PTR_ERR(file);
		goto err_put_unused_fd;
	}
	fd_install(fd, file);

	return fd;

err_put_unused_fd:
	put_unused_fd(fd);
	return error;
}
EXPORT_SYMBOL_GPL(anon_inode_getfd);

static int __init anon_inode_init(void)
{
	int error;

	error = register_filesystem(&anon_inode_fs_type);
	if (error)
		goto err_exit;
	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
	if (IS_ERR(anon_inode_mnt)) {
		error = PTR_ERR(anon_inode_mnt);
		goto err_unregister_filesystem;
	}
	return 0;

err_unregister_filesystem:
	unregister_filesystem(&anon_inode_fs_type);
err_exit:
	panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
}

fs_initcall(anon_inode_init);