blob: 47d4a01c53933afd77717c5e1616eda796055f78 [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};
Al Viro3ba13d12009-02-20 06:02:22 +000051static const struct dentry_operations anon_inodefs_dentry_operations = {
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070052 .d_delete = anon_inodefs_delete_dentry,
53};
54
Peter Zijlstrad3a92622009-06-18 12:54:00 +020055/*
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
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070068/**
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070069 * anon_inode_getfd - creates a new file instance by hooking it up to an
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070070 * anonymous inode, and a dentry that describe the "class"
71 * of the file
72 *
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070073 * @name: [in] name of the "class" of the new file
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070074 * @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
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070077 *
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.
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070080 * All the files created with anon_inode_getfd() will share a single inode,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070081 * hence saving memory and avoiding code duplication for the file/inode/dentry
Al Viro2030a422008-02-23 06:46:49 -050082 * setup. Returns new descriptor or -error.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070083 */
Al Viro2030a422008-02-23 06:46:49 -050084int anon_inode_getfd(const char *name, const struct file_operations *fops,
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070085 void *priv, int flags)
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070086{
87 struct qstr this;
88 struct dentry *dentry;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070089 struct file *file;
90 int error, fd;
91
92 if (IS_ERR(anon_inode_inode))
93 return -ENODEV;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070094
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +010095 if (fops->owner && !try_module_get(fops->owner))
96 return -ENOENT;
97
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070098 error = get_unused_fd_flags(flags);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070099 if (error < 0)
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +0100100 goto err_module;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700101 fd = error;
102
103 /*
104 * Link the inode to a directory entry by creating a unique name
105 * using the inode sequence number.
106 */
107 error = -ENOMEM;
108 this.name = name;
109 this.len = strlen(name);
110 this.hash = 0;
111 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
112 if (!dentry)
113 goto err_put_unused_fd;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700114
115 /*
116 * We know the anon_inode inode count is always greater than zero,
117 * so we can avoid doing an igrab() and we can use an open-coded
118 * atomic_inc().
119 */
120 atomic_inc(&anon_inode_inode->i_count);
121
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700122 dentry->d_op = &anon_inodefs_dentry_operations;
123 /* Do not publish this dentry inside the global dentry hash table */
124 dentry->d_flags &= ~DCACHE_UNHASHED;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700125 d_instantiate(dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700126
Dave Hansen430e2852008-02-15 14:37:26 -0800127 error = -ENFILE;
128 file = alloc_file(anon_inode_mnt, dentry,
129 FMODE_READ | FMODE_WRITE, fops);
130 if (!file)
131 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700132 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700133
134 file->f_pos = 0;
Ulrich Drepper99829b82008-07-23 21:29:33 -0700135 file->f_flags = O_RDWR | (flags & O_NONBLOCK);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700136 file->f_version = 0;
137 file->private_data = priv;
138
139 fd_install(fd, file);
140
Al Viro2030a422008-02-23 06:46:49 -0500141 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700142
Dave Hansen430e2852008-02-15 14:37:26 -0800143err_dput:
144 dput(dentry);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700145err_put_unused_fd:
146 put_unused_fd(fd);
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +0100147err_module:
148 module_put(fops->owner);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700149 return error;
150}
Avi Kivityd6d28162007-06-28 08:38:16 -0400151EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700152
153/*
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -0700154 * A single inode exists for all anon_inode files. Contrary to pipes,
155 * anon_inode inodes have no associated per-instance data, so we need
156 * only allocate one of them.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700157 */
158static struct inode *anon_inode_mkinode(void)
159{
160 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
161
162 if (!inode)
163 return ERR_PTR(-ENOMEM);
164
165 inode->i_fop = &anon_inode_fops;
166
Peter Zijlstrad3a92622009-06-18 12:54:00 +0200167 inode->i_mapping->a_ops = &anon_aops;
168
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700169 /*
170 * Mark the inode dirty from the very beginning,
171 * that way it will never be moved to the dirty
172 * list because mark_inode_dirty() will think
173 * that it already _is_ on the dirty list.
174 */
175 inode->i_state = I_DIRTY;
176 inode->i_mode = S_IRUSR | S_IWUSR;
David Howellsda9592e2008-11-14 10:39:05 +1100177 inode->i_uid = current_fsuid();
178 inode->i_gid = current_fsgid();
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700179 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
180 return inode;
181}
182
183static int __init anon_inode_init(void)
184{
185 int error;
186
187 error = register_filesystem(&anon_inode_fs_type);
188 if (error)
189 goto err_exit;
190 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
191 if (IS_ERR(anon_inode_mnt)) {
192 error = PTR_ERR(anon_inode_mnt);
193 goto err_unregister_filesystem;
194 }
195 anon_inode_inode = anon_inode_mkinode();
196 if (IS_ERR(anon_inode_inode)) {
197 error = PTR_ERR(anon_inode_inode);
198 goto err_mntput;
199 }
200
201 return 0;
202
203err_mntput:
204 mntput(anon_inode_mnt);
205err_unregister_filesystem:
206 unregister_filesystem(&anon_inode_fs_type);
207err_exit:
208 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
209}
210
211fs_initcall(anon_inode_init);
212