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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// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/anon_inodes.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 *
7 * Thanks to Arnd Bergmann for code review and suggestions.
8 * More changes for Thomas Gleixner suggestions.
9 *
10 */
11
12#include <linux/cred.h>
13#include <linux/file.h>
14#include <linux/poll.h>
15#include <linux/sched.h>
16#include <linux/init.h>
17#include <linux/fs.h>
18#include <linux/mount.h>
19#include <linux/module.h>
20#include <linux/kernel.h>
21#include <linux/magic.h>
22#include <linux/anon_inodes.h>
23#include <linux/pseudo_fs.h>
24
25#include <linux/uaccess.h>
26
27static struct vfsmount *anon_inode_mnt __read_mostly;
28static struct inode *anon_inode_inode;
29
30/*
31 * anon_inodefs_dname() is called from d_path().
32 */
33static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
34{
35 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
36 dentry->d_name.name);
37}
38
39static const struct dentry_operations anon_inodefs_dentry_operations = {
40 .d_dname = anon_inodefs_dname,
41};
42
43static int anon_inodefs_init_fs_context(struct fs_context *fc)
44{
45 struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
46 if (!ctx)
47 return -ENOMEM;
48 ctx->dops = &anon_inodefs_dentry_operations;
49 return 0;
50}
51
52static struct file_system_type anon_inode_fs_type = {
53 .name = "anon_inodefs",
54 .init_fs_context = anon_inodefs_init_fs_context,
55 .kill_sb = kill_anon_super,
56};
57
58/**
59 * anon_inode_getfile - creates a new file instance by hooking it up to an
60 * anonymous inode, and a dentry that describe the "class"
61 * of the file
62 *
63 * @name: [in] name of the "class" of the new file
64 * @fops: [in] file operations for the new file
65 * @priv: [in] private data for the new file (will be file's private_data)
66 * @flags: [in] flags
67 *
68 * Creates a new file by hooking it on a single inode. This is useful for files
69 * that do not need to have a full-fledged inode in order to operate correctly.
70 * All the files created with anon_inode_getfile() will share a single inode,
71 * hence saving memory and avoiding code duplication for the file/inode/dentry
72 * setup. Returns the newly created file* or an error pointer.
73 */
74struct file *anon_inode_getfile(const char *name,
75 const struct file_operations *fops,
76 void *priv, int flags)
77{
78 struct file *file;
79
80 if (IS_ERR(anon_inode_inode))
81 return ERR_PTR(-ENODEV);
82
83 if (fops->owner && !try_module_get(fops->owner))
84 return ERR_PTR(-ENOENT);
85
86 /*
87 * We know the anon_inode inode count is always greater than zero,
88 * so ihold() is safe.
89 */
90 ihold(anon_inode_inode);
91 file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
92 flags & (O_ACCMODE | O_NONBLOCK), fops);
93 if (IS_ERR(file))
94 goto err;
95
96 file->f_mapping = anon_inode_inode->i_mapping;
97
98 file->private_data = priv;
99
100 return file;
101
102err:
103 iput(anon_inode_inode);
104 module_put(fops->owner);
105 return file;
106}
107EXPORT_SYMBOL_GPL(anon_inode_getfile);
108
109/**
110 * anon_inode_getfd - creates a new file instance by hooking it up to an
111 * anonymous inode, and a dentry that describe the "class"
112 * of the file
113 *
114 * @name: [in] name of the "class" of the new file
115 * @fops: [in] file operations for the new file
116 * @priv: [in] private data for the new file (will be file's private_data)
117 * @flags: [in] flags
118 *
119 * Creates a new file by hooking it on a single inode. This is useful for files
120 * that do not need to have a full-fledged inode in order to operate correctly.
121 * All the files created with anon_inode_getfd() will share a single inode,
122 * hence saving memory and avoiding code duplication for the file/inode/dentry
123 * setup. Returns new descriptor or an error code.
124 */
125int anon_inode_getfd(const char *name, const struct file_operations *fops,
126 void *priv, int flags)
127{
128 int error, fd;
129 struct file *file;
130
131 error = get_unused_fd_flags(flags);
132 if (error < 0)
133 return error;
134 fd = error;
135
136 file = anon_inode_getfile(name, fops, priv, flags);
137 if (IS_ERR(file)) {
138 error = PTR_ERR(file);
139 goto err_put_unused_fd;
140 }
141 fd_install(fd, file);
142
143 return fd;
144
145err_put_unused_fd:
146 put_unused_fd(fd);
147 return error;
148}
149EXPORT_SYMBOL_GPL(anon_inode_getfd);
150
151static int __init anon_inode_init(void)
152{
153 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
154 if (IS_ERR(anon_inode_mnt))
155 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
156
157 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
158 if (IS_ERR(anon_inode_inode))
159 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
160
161 return 0;
162}
163
164fs_initcall(anon_inode_init);
165