blob: 977ef208c05193bbe555a4b4bce50853f0483616 [file] [log] [blame]
Davide Libenzi5dc8bf82007-05-10 22:23:11 -07001/*
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/file.h>
12#include <linux/poll.h>
13#include <linux/slab.h>
14#include <linux/init.h>
15#include <linux/fs.h>
16#include <linux/mount.h>
17#include <linux/module.h>
18#include <linux/kernel.h>
19#include <linux/magic.h>
20#include <linux/anon_inodes.h>
21
22#include <asm/uaccess.h>
23
24static struct vfsmount *anon_inode_mnt __read_mostly;
25static struct inode *anon_inode_inode;
26static const struct file_operations anon_inode_fops;
27
28static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
29 const char *dev_name, void *data,
30 struct vfsmount *mnt)
31{
32 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
33 mnt);
34}
35
36static int anon_inodefs_delete_dentry(struct dentry *dentry)
37{
38 /*
39 * We faked vfs to believe the dentry was hashed when we created it.
40 * Now we restore the flag so that dput() will work correctly.
41 */
42 dentry->d_flags |= DCACHE_UNHASHED;
43 return 1;
44}
45
46static struct file_system_type anon_inode_fs_type = {
47 .name = "anon_inodefs",
48 .get_sb = anon_inodefs_get_sb,
49 .kill_sb = kill_anon_super,
50};
51static struct dentry_operations anon_inodefs_dentry_operations = {
52 .d_delete = anon_inodefs_delete_dentry,
53};
54
55/**
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070056 * anon_inode_getfd - creates a new file instance by hooking it up to an
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070057 * anonymous inode, and a dentry that describe the "class"
58 * of the file
59 *
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070060 * @name: [in] name of the "class" of the new file
61 * @fops [in] file operations for the new file
62 * @priv [in] private data for the new file (will be file's private_data)
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.
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070066 * All the files created with anon_inode_getfd() will share a single inode,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070067 * hence saving memory and avoiding code duplication for the file/inode/dentry
Al Viro2030a422008-02-23 06:46:49 -050068 * setup. Returns new descriptor or -error.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070069 */
Al Viro2030a422008-02-23 06:46:49 -050070int anon_inode_getfd(const char *name, const struct file_operations *fops,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070071 void *priv)
72{
73 struct qstr this;
74 struct dentry *dentry;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070075 struct file *file;
76 int error, fd;
77
78 if (IS_ERR(anon_inode_inode))
79 return -ENODEV;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070080
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070081 error = get_unused_fd();
82 if (error < 0)
Dave Hansen430e2852008-02-15 14:37:26 -080083 return error;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070084 fd = error;
85
86 /*
87 * Link the inode to a directory entry by creating a unique name
88 * using the inode sequence number.
89 */
90 error = -ENOMEM;
91 this.name = name;
92 this.len = strlen(name);
93 this.hash = 0;
94 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
95 if (!dentry)
96 goto err_put_unused_fd;
Davide Libenzi96fdc722007-10-16 23:30:19 -070097
98 /*
99 * We know the anon_inode inode count is always greater than zero,
100 * so we can avoid doing an igrab() and we can use an open-coded
101 * atomic_inc().
102 */
103 atomic_inc(&anon_inode_inode->i_count);
104
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700105 dentry->d_op = &anon_inodefs_dentry_operations;
106 /* Do not publish this dentry inside the global dentry hash table */
107 dentry->d_flags &= ~DCACHE_UNHASHED;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700108 d_instantiate(dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700109
Dave Hansen430e2852008-02-15 14:37:26 -0800110 error = -ENFILE;
111 file = alloc_file(anon_inode_mnt, dentry,
112 FMODE_READ | FMODE_WRITE, fops);
113 if (!file)
114 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700115 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700116
117 file->f_pos = 0;
118 file->f_flags = O_RDWR;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700119 file->f_version = 0;
120 file->private_data = priv;
121
122 fd_install(fd, file);
123
Al Viro2030a422008-02-23 06:46:49 -0500124 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700125
Dave Hansen430e2852008-02-15 14:37:26 -0800126err_dput:
127 dput(dentry);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700128err_put_unused_fd:
129 put_unused_fd(fd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700130 return error;
131}
Avi Kivityd6d28162007-06-28 08:38:16 -0400132EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700133
134/*
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -0700135 * A single inode exists for all anon_inode files. Contrary to pipes,
136 * anon_inode inodes have no associated per-instance data, so we need
137 * only allocate one of them.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700138 */
139static struct inode *anon_inode_mkinode(void)
140{
141 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
142
143 if (!inode)
144 return ERR_PTR(-ENOMEM);
145
146 inode->i_fop = &anon_inode_fops;
147
148 /*
149 * Mark the inode dirty from the very beginning,
150 * that way it will never be moved to the dirty
151 * list because mark_inode_dirty() will think
152 * that it already _is_ on the dirty list.
153 */
154 inode->i_state = I_DIRTY;
155 inode->i_mode = S_IRUSR | S_IWUSR;
156 inode->i_uid = current->fsuid;
157 inode->i_gid = current->fsgid;
158 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
159 return inode;
160}
161
162static int __init anon_inode_init(void)
163{
164 int error;
165
166 error = register_filesystem(&anon_inode_fs_type);
167 if (error)
168 goto err_exit;
169 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
170 if (IS_ERR(anon_inode_mnt)) {
171 error = PTR_ERR(anon_inode_mnt);
172 goto err_unregister_filesystem;
173 }
174 anon_inode_inode = anon_inode_mkinode();
175 if (IS_ERR(anon_inode_inode)) {
176 error = PTR_ERR(anon_inode_inode);
177 goto err_mntput;
178 }
179
180 return 0;
181
182err_mntput:
183 mntput(anon_inode_mnt);
184err_unregister_filesystem:
185 unregister_filesystem(&anon_inode_fs_type);
186err_exit:
187 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
188}
189
190fs_initcall(anon_inode_init);
191