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
25 static struct vfsmount *anon_inode_mnt __read_mostly;
26 static struct inode *anon_inode_inode;
27
28 /*
29 * anon_inodefs_dname() is called from d_path().
30 */
anon_inodefs_dname(struct dentry * dentry,char * buffer,int buflen)31 static 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
37 static const struct dentry_operations anon_inodefs_dentry_operations = {
38 .d_dname = anon_inodefs_dname,
39 };
40
anon_inodefs_mount(struct file_system_type * fs_type,int flags,const char * dev_name,void * data)41 static 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
48 static 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 */
anon_inode_getfile(const char * name,const struct file_operations * fops,void * priv,int flags)70 struct file *anon_inode_getfile(const char *name,
71 const struct file_operations *fops,
72 void *priv, int flags)
73 {
74 struct file *file;
75
76 if (IS_ERR(anon_inode_inode))
77 return ERR_PTR(-ENODEV);
78
79 if (fops->owner && !try_module_get(fops->owner))
80 return ERR_PTR(-ENOENT);
81
82 /*
83 * We know the anon_inode inode count is always greater than zero,
84 * so ihold() is safe.
85 */
86 ihold(anon_inode_inode);
87 file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
88 flags & (O_ACCMODE | O_NONBLOCK), fops);
89 if (IS_ERR(file))
90 goto err;
91
92 file->f_mapping = anon_inode_inode->i_mapping;
93
94 file->private_data = priv;
95
96 return file;
97
98 err:
99 iput(anon_inode_inode);
100 module_put(fops->owner);
101 return file;
102 }
103 EXPORT_SYMBOL_GPL(anon_inode_getfile);
104
105 /**
106 * anon_inode_getfd - creates a new file instance by hooking it up to an
107 * anonymous inode, and a dentry that describe the "class"
108 * of the file
109 *
110 * @name: [in] name of the "class" of the new file
111 * @fops: [in] file operations for the new file
112 * @priv: [in] private data for the new file (will be file's private_data)
113 * @flags: [in] flags
114 *
115 * Creates a new file by hooking it on a single inode. This is useful for files
116 * that do not need to have a full-fledged inode in order to operate correctly.
117 * All the files created with anon_inode_getfd() will share a single inode,
118 * hence saving memory and avoiding code duplication for the file/inode/dentry
119 * setup. Returns new descriptor or an error code.
120 */
anon_inode_getfd(const char * name,const struct file_operations * fops,void * priv,int flags)121 int anon_inode_getfd(const char *name, const struct file_operations *fops,
122 void *priv, int flags)
123 {
124 int error, fd;
125 struct file *file;
126
127 error = get_unused_fd_flags(flags);
128 if (error < 0)
129 return error;
130 fd = error;
131
132 file = anon_inode_getfile(name, fops, priv, flags);
133 if (IS_ERR(file)) {
134 error = PTR_ERR(file);
135 goto err_put_unused_fd;
136 }
137 fd_install(fd, file);
138
139 return fd;
140
141 err_put_unused_fd:
142 put_unused_fd(fd);
143 return error;
144 }
145 EXPORT_SYMBOL_GPL(anon_inode_getfd);
146
anon_inode_init(void)147 static int __init anon_inode_init(void)
148 {
149 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
150 if (IS_ERR(anon_inode_mnt))
151 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
152
153 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
154 if (IS_ERR(anon_inode_inode))
155 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
156
157 return 0;
158 }
159
160 fs_initcall(anon_inode_init);
161
162
