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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
Alexey Dobriyana99bbaf2009-10-04 16:11:37 +040011#include <linux/cred.h>
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070012#include <linux/file.h>
13#include <linux/poll.h>
Alexey Dobriyana99bbaf2009-10-04 16:11:37 +040014#include <linux/sched.h>
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070015#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 <asm/uaccess.h>
24
25static struct vfsmount *anon_inode_mnt __read_mostly;
26static struct inode *anon_inode_inode;
27static const struct file_operations anon_inode_fops;
28
29static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
30 const char *dev_name, void *data,
31 struct vfsmount *mnt)
32{
33 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
34 mnt);
35}
36
Nick Pigginb9aff022009-11-20 14:28:35 -080037/*
38 * anon_inodefs_dname() is called from d_path().
39 */
40static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
41{
42 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
43 dentry->d_name.name);
44}
45
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070046static 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 = {
Nick Pigginb9aff022009-11-20 14:28:35 -080052 .d_dname = anon_inodefs_dname,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070053};
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.
Davide Libenzi562787a2009-09-22 16:43:57 -070080 * All the files created with anon_inode_getfile() 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
Davide Libenzi562787a2009-09-22 16:43:57 -070082 * setup. Returns the newly created file* or an error pointer.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070083 */
Davide Libenzi562787a2009-09-22 16:43:57 -070084struct file *anon_inode_getfile(const char *name,
85 const struct file_operations *fops,
86 void *priv, int flags)
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070087{
88 struct qstr this;
Al Viro2c48b9c2009-08-09 00:52:35 +040089 struct path path;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070090 struct file *file;
Davide Libenzi562787a2009-09-22 16:43:57 -070091 int error;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070092
93 if (IS_ERR(anon_inode_inode))
Davide Libenzi562787a2009-09-22 16:43:57 -070094 return ERR_PTR(-ENODEV);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070095
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +010096 if (fops->owner && !try_module_get(fops->owner))
Davide Libenzi562787a2009-09-22 16:43:57 -070097 return ERR_PTR(-ENOENT);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070098
99 /*
100 * Link the inode to a directory entry by creating a unique name
101 * using the inode sequence number.
102 */
103 error = -ENOMEM;
104 this.name = name;
105 this.len = strlen(name);
106 this.hash = 0;
Al Viro2c48b9c2009-08-09 00:52:35 +0400107 path.dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
108 if (!path.dentry)
Davide Libenzi562787a2009-09-22 16:43:57 -0700109 goto err_module;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700110
Al Viro2c48b9c2009-08-09 00:52:35 +0400111 path.mnt = mntget(anon_inode_mnt);
Davide Libenzi96fdc722007-10-16 23:30:19 -0700112 /*
113 * We know the anon_inode inode count is always greater than zero,
114 * so we can avoid doing an igrab() and we can use an open-coded
115 * atomic_inc().
116 */
117 atomic_inc(&anon_inode_inode->i_count);
118
Al Viro2c48b9c2009-08-09 00:52:35 +0400119 path.dentry->d_op = &anon_inodefs_dentry_operations;
Al Viro2c48b9c2009-08-09 00:52:35 +0400120 d_instantiate(path.dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700121
Dave Hansen430e2852008-02-15 14:37:26 -0800122 error = -ENFILE;
Al Viro53009902009-12-19 10:15:07 -0500123 file = alloc_file(&path, OPEN_FMODE(flags), fops);
Dave Hansen430e2852008-02-15 14:37:26 -0800124 if (!file)
125 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700126 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700127
128 file->f_pos = 0;
Roland Dreier628ff7c2009-12-18 09:41:24 -0800129 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700130 file->f_version = 0;
131 file->private_data = priv;
132
Davide Libenzi562787a2009-09-22 16:43:57 -0700133 return file;
134
135err_dput:
Al Viro2c48b9c2009-08-09 00:52:35 +0400136 path_put(&path);
Davide Libenzi562787a2009-09-22 16:43:57 -0700137err_module:
138 module_put(fops->owner);
139 return ERR_PTR(error);
140}
141EXPORT_SYMBOL_GPL(anon_inode_getfile);
142
143/**
144 * anon_inode_getfd - creates a new file instance by hooking it up to an
145 * anonymous inode, and a dentry that describe the "class"
146 * of the file
147 *
148 * @name: [in] name of the "class" of the new file
149 * @fops: [in] file operations for the new file
150 * @priv: [in] private data for the new file (will be file's private_data)
151 * @flags: [in] flags
152 *
153 * Creates a new file by hooking it on a single inode. This is useful for files
154 * that do not need to have a full-fledged inode in order to operate correctly.
155 * All the files created with anon_inode_getfd() will share a single inode,
156 * hence saving memory and avoiding code duplication for the file/inode/dentry
157 * setup. Returns new descriptor or an error code.
158 */
159int anon_inode_getfd(const char *name, const struct file_operations *fops,
160 void *priv, int flags)
161{
162 int error, fd;
163 struct file *file;
164
165 error = get_unused_fd_flags(flags);
166 if (error < 0)
167 return error;
168 fd = error;
169
170 file = anon_inode_getfile(name, fops, priv, flags);
171 if (IS_ERR(file)) {
172 error = PTR_ERR(file);
173 goto err_put_unused_fd;
174 }
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700175 fd_install(fd, file);
176
Al Viro2030a422008-02-23 06:46:49 -0500177 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700178
179err_put_unused_fd:
180 put_unused_fd(fd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700181 return error;
182}
Avi Kivityd6d28162007-06-28 08:38:16 -0400183EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700184
185/*
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -0700186 * A single inode exists for all anon_inode files. Contrary to pipes,
187 * anon_inode inodes have no associated per-instance data, so we need
188 * only allocate one of them.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700189 */
190static struct inode *anon_inode_mkinode(void)
191{
192 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
193
194 if (!inode)
195 return ERR_PTR(-ENOMEM);
196
197 inode->i_fop = &anon_inode_fops;
198
Peter Zijlstrad3a92622009-06-18 12:54:00 +0200199 inode->i_mapping->a_ops = &anon_aops;
200
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700201 /*
202 * Mark the inode dirty from the very beginning,
203 * that way it will never be moved to the dirty
204 * list because mark_inode_dirty() will think
205 * that it already _is_ on the dirty list.
206 */
207 inode->i_state = I_DIRTY;
208 inode->i_mode = S_IRUSR | S_IWUSR;
David Howellsda9592e2008-11-14 10:39:05 +1100209 inode->i_uid = current_fsuid();
210 inode->i_gid = current_fsgid();
Eric Paris3836a032010-03-09 22:23:01 -0500211 inode->i_flags |= S_PRIVATE;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700212 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
213 return inode;
214}
215
216static int __init anon_inode_init(void)
217{
218 int error;
219
220 error = register_filesystem(&anon_inode_fs_type);
221 if (error)
222 goto err_exit;
223 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
224 if (IS_ERR(anon_inode_mnt)) {
225 error = PTR_ERR(anon_inode_mnt);
226 goto err_unregister_filesystem;
227 }
228 anon_inode_inode = anon_inode_mkinode();
229 if (IS_ERR(anon_inode_inode)) {
230 error = PTR_ERR(anon_inode_inode);
231 goto err_mntput;
232 }
233
234 return 0;
235
236err_mntput:
237 mntput(anon_inode_mnt);
238err_unregister_filesystem:
239 unregister_filesystem(&anon_inode_fs_type);
240err_exit:
241 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
242}
243
244fs_initcall(anon_inode_init);
245