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1/*
2 * fs/anon_inodes.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 * Thanks to Arnd Bergmann for code review and suggestions.
7 * More changes for Thomas Gleixner suggestions.
8 *
9 */
10
11#include <linux/cred.h>
12#include <linux/file.h>
13#include <linux/poll.h>
14#include <linux/sched.h>
15#include <linux/init.h>
16#include <linux/fs.h>
17#include <linux/mount.h>
18#include <linux/module.h>
19#include <linux/kernel.h>
20#include <linux/magic.h>
21#include <linux/anon_inodes.h>
22
23#include <linux/uaccess.h>
24
25static struct vfsmount *anon_inode_mnt __read_mostly;
26static struct inode *anon_inode_inode;
27
28/*
29 * anon_inodefs_dname() is called from d_path().
30 */
31static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
32{
33 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
34 dentry->d_name.name);
35}
36
37static const struct dentry_operations anon_inodefs_dentry_operations = {
38 .d_dname = anon_inodefs_dname,
39};
40
41static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
42 int flags, const char *dev_name, void *data)
43{
44 return mount_pseudo(fs_type, "anon_inode:", NULL,
45 &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
46}
47
48static struct file_system_type anon_inode_fs_type = {
49 .name = "anon_inodefs",
50 .mount = anon_inodefs_mount,
51 .kill_sb = kill_anon_super,
52};
53
54/**
55 * anon_inode_getfile - creates a new file instance by hooking it up to an
56 * anonymous inode, and a dentry that describe the "class"
57 * of the file
58 *
59 * @name: [in] name of the "class" of the new file
60 * @fops: [in] file operations for the new file
61 * @priv: [in] private data for the new file (will be file's private_data)
62 * @flags: [in] flags
63 *
64 * Creates a new file by hooking it on a single inode. This is useful for files
65 * that do not need to have a full-fledged inode in order to operate correctly.
66 * All the files created with anon_inode_getfile() will share a single inode,
67 * hence saving memory and avoiding code duplication for the file/inode/dentry
68 * setup. Returns the newly created file* or an error pointer.
69 */
70struct file *anon_inode_getfile(const char *name,
71 const struct file_operations *fops,
72 void *priv, int flags)
73{
74 struct qstr this;
75 struct path path;
76 struct file *file;
77
78 if (IS_ERR(anon_inode_inode))
79 return ERR_PTR(-ENODEV);
80
81 if (fops->owner && !try_module_get(fops->owner))
82 return ERR_PTR(-ENOENT);
83
84 /*
85 * Link the inode to a directory entry by creating a unique name
86 * using the inode sequence number.
87 */
88 file = ERR_PTR(-ENOMEM);
89 this.name = name;
90 this.len = strlen(name);
91 this.hash = 0;
92 path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
93 if (!path.dentry)
94 goto err_module;
95
96 path.mnt = mntget(anon_inode_mnt);
97 /*
98 * We know the anon_inode inode count is always greater than zero,
99 * so ihold() is safe.
100 */
101 ihold(anon_inode_inode);
102
103 d_instantiate(path.dentry, anon_inode_inode);
104
105 file = alloc_file(&path, OPEN_FMODE(flags), fops);
106 if (IS_ERR(file))
107 goto err_dput;
108 file->f_mapping = anon_inode_inode->i_mapping;
109
110 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
111 file->private_data = priv;
112
113 return file;
114
115err_dput:
116 path_put(&path);
117err_module:
118 module_put(fops->owner);
119 return file;
120}
121EXPORT_SYMBOL_GPL(anon_inode_getfile);
122
123/**
124 * anon_inode_getfd - creates a new file instance by hooking it up to an
125 * anonymous inode, and a dentry that describe the "class"
126 * of the file
127 *
128 * @name: [in] name of the "class" of the new file
129 * @fops: [in] file operations for the new file
130 * @priv: [in] private data for the new file (will be file's private_data)
131 * @flags: [in] flags
132 *
133 * Creates a new file by hooking it on a single inode. This is useful for files
134 * that do not need to have a full-fledged inode in order to operate correctly.
135 * All the files created with anon_inode_getfd() will share a single inode,
136 * hence saving memory and avoiding code duplication for the file/inode/dentry
137 * setup. Returns new descriptor or an error code.
138 */
139int anon_inode_getfd(const char *name, const struct file_operations *fops,
140 void *priv, int flags)
141{
142 int error, fd;
143 struct file *file;
144
145 error = get_unused_fd_flags(flags);
146 if (error < 0)
147 return error;
148 fd = error;
149
150 file = anon_inode_getfile(name, fops, priv, flags);
151 if (IS_ERR(file)) {
152 error = PTR_ERR(file);
153 goto err_put_unused_fd;
154 }
155 fd_install(fd, file);
156
157 return fd;
158
159err_put_unused_fd:
160 put_unused_fd(fd);
161 return error;
162}
163EXPORT_SYMBOL_GPL(anon_inode_getfd);
164
165static int __init anon_inode_init(void)
166{
167 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
168 if (IS_ERR(anon_inode_mnt))
169 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
170
171 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
172 if (IS_ERR(anon_inode_inode))
173 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
174
175 return 0;
176}
177
178fs_initcall(anon_inode_init);
179
1/*
2 * fs/anon_inodes.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 * Thanks to Arnd Bergmann for code review and suggestions.
7 * More changes for Thomas Gleixner suggestions.
8 *
9 */
10
11#include <linux/cred.h>
12#include <linux/file.h>
13#include <linux/poll.h>
14#include <linux/sched.h>
15#include <linux/init.h>
16#include <linux/fs.h>
17#include <linux/mount.h>
18#include <linux/module.h>
19#include <linux/kernel.h>
20#include <linux/magic.h>
21#include <linux/anon_inodes.h>
22
23#include <asm/uaccess.h>
24
25static struct vfsmount *anon_inode_mnt __read_mostly;
26static struct inode *anon_inode_inode;
27static const struct file_operations anon_inode_fops;
28
29/*
30 * anon_inodefs_dname() is called from d_path().
31 */
32static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
33{
34 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
35 dentry->d_name.name);
36}
37
38static const struct dentry_operations anon_inodefs_dentry_operations = {
39 .d_dname = anon_inodefs_dname,
40};
41
42static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
43 int flags, const char *dev_name, void *data)
44{
45 return mount_pseudo(fs_type, "anon_inode:", NULL,
46 &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
47}
48
49static struct file_system_type anon_inode_fs_type = {
50 .name = "anon_inodefs",
51 .mount = anon_inodefs_mount,
52 .kill_sb = kill_anon_super,
53};
54
55/*
56 * nop .set_page_dirty method so that people can use .page_mkwrite on
57 * anon inodes.
58 */
59static int anon_set_page_dirty(struct page *page)
60{
61 return 0;
62};
63
64static const struct address_space_operations anon_aops = {
65 .set_page_dirty = anon_set_page_dirty,
66};
67
68/**
69 * anon_inode_getfile - creates a new file instance by hooking it up to an
70 * anonymous inode, and a dentry that describe the "class"
71 * of the file
72 *
73 * @name: [in] name of the "class" of the new file
74 * @fops: [in] file operations for the new file
75 * @priv: [in] private data for the new file (will be file's private_data)
76 * @flags: [in] flags
77 *
78 * Creates a new file by hooking it on a single inode. This is useful for files
79 * that do not need to have a full-fledged inode in order to operate correctly.
80 * All the files created with anon_inode_getfile() will share a single inode,
81 * hence saving memory and avoiding code duplication for the file/inode/dentry
82 * setup. Returns the newly created file* or an error pointer.
83 */
84struct file *anon_inode_getfile(const char *name,
85 const struct file_operations *fops,
86 void *priv, int flags)
87{
88 struct qstr this;
89 struct path path;
90 struct file *file;
91 int error;
92
93 if (IS_ERR(anon_inode_inode))
94 return ERR_PTR(-ENODEV);
95
96 if (fops->owner && !try_module_get(fops->owner))
97 return ERR_PTR(-ENOENT);
98
99 /*
100 * Link the inode to a directory entry by creating a unique name
101 * using the inode sequence number.
102 */
103 error = -ENOMEM;
104 this.name = name;
105 this.len = strlen(name);
106 this.hash = 0;
107 path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
108 if (!path.dentry)
109 goto err_module;
110
111 path.mnt = mntget(anon_inode_mnt);
112 /*
113 * We know the anon_inode inode count is always greater than zero,
114 * so ihold() is safe.
115 */
116 ihold(anon_inode_inode);
117
118 d_instantiate(path.dentry, anon_inode_inode);
119
120 error = -ENFILE;
121 file = alloc_file(&path, OPEN_FMODE(flags), fops);
122 if (!file)
123 goto err_dput;
124 file->f_mapping = anon_inode_inode->i_mapping;
125
126 file->f_pos = 0;
127 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
128 file->f_version = 0;
129 file->private_data = priv;
130
131 return file;
132
133err_dput:
134 path_put(&path);
135err_module:
136 module_put(fops->owner);
137 return ERR_PTR(error);
138}
139EXPORT_SYMBOL_GPL(anon_inode_getfile);
140
141/**
142 * anon_inode_getfd - creates a new file instance by hooking it up to an
143 * anonymous inode, and a dentry that describe the "class"
144 * of the file
145 *
146 * @name: [in] name of the "class" of the new file
147 * @fops: [in] file operations for the new file
148 * @priv: [in] private data for the new file (will be file's private_data)
149 * @flags: [in] flags
150 *
151 * Creates a new file by hooking it on a single inode. This is useful for files
152 * that do not need to have a full-fledged inode in order to operate correctly.
153 * All the files created with anon_inode_getfd() will share a single inode,
154 * hence saving memory and avoiding code duplication for the file/inode/dentry
155 * setup. Returns new descriptor or an error code.
156 */
157int anon_inode_getfd(const char *name, const struct file_operations *fops,
158 void *priv, int flags)
159{
160 int error, fd;
161 struct file *file;
162
163 error = get_unused_fd_flags(flags);
164 if (error < 0)
165 return error;
166 fd = error;
167
168 file = anon_inode_getfile(name, fops, priv, flags);
169 if (IS_ERR(file)) {
170 error = PTR_ERR(file);
171 goto err_put_unused_fd;
172 }
173 fd_install(fd, file);
174
175 return fd;
176
177err_put_unused_fd:
178 put_unused_fd(fd);
179 return error;
180}
181EXPORT_SYMBOL_GPL(anon_inode_getfd);
182
183/*
184 * A single inode exists for all anon_inode files. Contrary to pipes,
185 * anon_inode inodes have no associated per-instance data, so we need
186 * only allocate one of them.
187 */
188static struct inode *anon_inode_mkinode(void)
189{
190 struct inode *inode = new_inode_pseudo(anon_inode_mnt->mnt_sb);
191
192 if (!inode)
193 return ERR_PTR(-ENOMEM);
194
195 inode->i_ino = get_next_ino();
196 inode->i_fop = &anon_inode_fops;
197
198 inode->i_mapping->a_ops = &anon_aops;
199
200 /*
201 * Mark the inode dirty from the very beginning,
202 * that way it will never be moved to the dirty
203 * list because mark_inode_dirty() will think
204 * that it already _is_ on the dirty list.
205 */
206 inode->i_state = I_DIRTY;
207 inode->i_mode = S_IRUSR | S_IWUSR;
208 inode->i_uid = current_fsuid();
209 inode->i_gid = current_fsgid();
210 inode->i_flags |= S_PRIVATE;
211 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
212 return inode;
213}
214
215static int __init anon_inode_init(void)
216{
217 int error;
218
219 error = register_filesystem(&anon_inode_fs_type);
220 if (error)
221 goto err_exit;
222 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
223 if (IS_ERR(anon_inode_mnt)) {
224 error = PTR_ERR(anon_inode_mnt);
225 goto err_unregister_filesystem;
226 }
227 anon_inode_inode = anon_inode_mkinode();
228 if (IS_ERR(anon_inode_inode)) {
229 error = PTR_ERR(anon_inode_inode);
230 goto err_mntput;
231 }
232
233 return 0;
234
235err_mntput:
236 kern_unmount(anon_inode_mnt);
237err_unregister_filesystem:
238 unregister_filesystem(&anon_inode_fs_type);
239err_exit:
240 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
241}
242
243fs_initcall(anon_inode_init);
244