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
27 static struct vfsmount *anon_inode_mnt __read_mostly;
28 static struct inode *anon_inode_inode;
29
30 /*
31 * anon_inodefs_dname() is called from d_path().
32 */
anon_inodefs_dname(struct dentry * dentry,char * buffer,int buflen)33 static 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
39 static const struct dentry_operations anon_inodefs_dentry_operations = {
40 .d_dname = anon_inodefs_dname,
41 };
42
anon_inodefs_init_fs_context(struct fs_context * fc)43 static 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
52 static 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 */
anon_inode_getfile(const char * name,const struct file_operations * fops,void * priv,int flags)74 struct 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
102 err:
103 iput(anon_inode_inode);
104 module_put(fops->owner);
105 return file;
106 }
107 EXPORT_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 */
anon_inode_getfd(const char * name,const struct file_operations * fops,void * priv,int flags)125 int 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
145 err_put_unused_fd:
146 put_unused_fd(fd);
147 return error;
148 }
149 EXPORT_SYMBOL_GPL(anon_inode_getfd);
150
anon_inode_init(void)151 static 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
164 fs_initcall(anon_inode_init);
165
166
