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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
Nick Pigginb9aff022009-11-20 14:28:35 -080029/*
30 * anon_inodefs_dname() is called from d_path().
31 */
32static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
33{
34 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
35 dentry->d_name.name);
36}
37
Al Viroc74a1cb2011-01-12 16:59:34 -050038static const struct dentry_operations anon_inodefs_dentry_operations = {
39 .d_dname = anon_inodefs_dname,
40};
41
Peter Zijlstrad3a92622009-06-18 12:54:00 +020042/*
43 * nop .set_page_dirty method so that people can use .page_mkwrite on
44 * anon inodes.
45 */
46static int anon_set_page_dirty(struct page *page)
47{
48 return 0;
49};
50
51static const struct address_space_operations anon_aops = {
52 .set_page_dirty = anon_set_page_dirty,
53};
54
Al Viroca7068c2012-03-17 02:52:29 -040055/*
56 * A single inode exists for all anon_inode files. Contrary to pipes,
57 * anon_inode inodes have no associated per-instance data, so we need
58 * only allocate one of them.
59 */
60static struct inode *anon_inode_mkinode(struct super_block *s)
61{
62 struct inode *inode = new_inode_pseudo(s);
63
64 if (!inode)
65 return ERR_PTR(-ENOMEM);
66
67 inode->i_ino = get_next_ino();
68 inode->i_fop = &anon_inode_fops;
69
70 inode->i_mapping->a_ops = &anon_aops;
71
72 /*
73 * Mark the inode dirty from the very beginning,
74 * that way it will never be moved to the dirty
75 * list because mark_inode_dirty() will think
76 * that it already _is_ on the dirty list.
77 */
78 inode->i_state = I_DIRTY;
79 inode->i_mode = S_IRUSR | S_IWUSR;
80 inode->i_uid = current_fsuid();
81 inode->i_gid = current_fsgid();
82 inode->i_flags |= S_PRIVATE;
83 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
84 return inode;
85}
86
87static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
88 int flags, const char *dev_name, void *data)
89{
90 struct dentry *root;
91 root = mount_pseudo(fs_type, "anon_inode:", NULL,
92 &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
93 if (!IS_ERR(root)) {
94 struct super_block *s = root->d_sb;
95 anon_inode_inode = anon_inode_mkinode(s);
96 if (IS_ERR(anon_inode_inode)) {
97 dput(root);
98 deactivate_locked_super(s);
99 root = ERR_CAST(anon_inode_inode);
100 }
101 }
102 return root;
103}
104
105static struct file_system_type anon_inode_fs_type = {
106 .name = "anon_inodefs",
107 .mount = anon_inodefs_mount,
108 .kill_sb = kill_anon_super,
109};
110
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700111/**
Namhyung Kimc0d87682010-12-10 12:11:50 +0900112 * anon_inode_getfile - creates a new file instance by hooking it up to an
113 * anonymous inode, and a dentry that describe the "class"
114 * of the file
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700115 *
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700116 * @name: [in] name of the "class" of the new file
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -0700117 * @fops: [in] file operations for the new file
118 * @priv: [in] private data for the new file (will be file's private_data)
119 * @flags: [in] flags
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700120 *
121 * Creates a new file by hooking it on a single inode. This is useful for files
122 * that do not need to have a full-fledged inode in order to operate correctly.
Davide Libenzi562787a2009-09-22 16:43:57 -0700123 * All the files created with anon_inode_getfile() will share a single inode,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700124 * hence saving memory and avoiding code duplication for the file/inode/dentry
Davide Libenzi562787a2009-09-22 16:43:57 -0700125 * setup. Returns the newly created file* or an error pointer.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700126 */
Davide Libenzi562787a2009-09-22 16:43:57 -0700127struct file *anon_inode_getfile(const char *name,
128 const struct file_operations *fops,
129 void *priv, int flags)
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700130{
131 struct qstr this;
Al Viro2c48b9c2009-08-09 00:52:35 +0400132 struct path path;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700133 struct file *file;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700134
135 if (IS_ERR(anon_inode_inode))
Davide Libenzi562787a2009-09-22 16:43:57 -0700136 return ERR_PTR(-ENODEV);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700137
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +0100138 if (fops->owner && !try_module_get(fops->owner))
Davide Libenzi562787a2009-09-22 16:43:57 -0700139 return ERR_PTR(-ENOENT);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700140
141 /*
142 * Link the inode to a directory entry by creating a unique name
143 * using the inode sequence number.
144 */
Anatol Pomozov39b65252012-09-12 20:11:55 -0700145 file = ERR_PTR(-ENOMEM);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700146 this.name = name;
147 this.len = strlen(name);
148 this.hash = 0;
Nick Piggin4b936882011-01-07 17:50:07 +1100149 path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
Al Viro2c48b9c2009-08-09 00:52:35 +0400150 if (!path.dentry)
Davide Libenzi562787a2009-09-22 16:43:57 -0700151 goto err_module;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700152
Al Viro2c48b9c2009-08-09 00:52:35 +0400153 path.mnt = mntget(anon_inode_mnt);
Davide Libenzi96fdc722007-10-16 23:30:19 -0700154 /*
155 * We know the anon_inode inode count is always greater than zero,
Al Viro7de9c6ee2010-10-23 11:11:40 -0400156 * so ihold() is safe.
Davide Libenzi96fdc722007-10-16 23:30:19 -0700157 */
Al Viro7de9c6ee2010-10-23 11:11:40 -0400158 ihold(anon_inode_inode);
Davide Libenzi96fdc722007-10-16 23:30:19 -0700159
Al Viro2c48b9c2009-08-09 00:52:35 +0400160 d_instantiate(path.dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700161
Al Viro53009902009-12-19 10:15:07 -0500162 file = alloc_file(&path, OPEN_FMODE(flags), fops);
Anatol Pomozov39b65252012-09-12 20:11:55 -0700163 if (IS_ERR(file))
Dave Hansen430e2852008-02-15 14:37:26 -0800164 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700165 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700166
Roland Dreier628ff7c2009-12-18 09:41:24 -0800167 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700168 file->private_data = priv;
169
Davide Libenzi562787a2009-09-22 16:43:57 -0700170 return file;
171
172err_dput:
Al Viro2c48b9c2009-08-09 00:52:35 +0400173 path_put(&path);
Davide Libenzi562787a2009-09-22 16:43:57 -0700174err_module:
175 module_put(fops->owner);
Anatol Pomozov39b65252012-09-12 20:11:55 -0700176 return file;
Davide Libenzi562787a2009-09-22 16:43:57 -0700177}
178EXPORT_SYMBOL_GPL(anon_inode_getfile);
179
180/**
181 * anon_inode_getfd - creates a new file instance by hooking it up to an
182 * anonymous inode, and a dentry that describe the "class"
183 * of the file
184 *
185 * @name: [in] name of the "class" of the new file
186 * @fops: [in] file operations for the new file
187 * @priv: [in] private data for the new file (will be file's private_data)
188 * @flags: [in] flags
189 *
190 * Creates a new file by hooking it on a single inode. This is useful for files
191 * that do not need to have a full-fledged inode in order to operate correctly.
192 * All the files created with anon_inode_getfd() will share a single inode,
193 * hence saving memory and avoiding code duplication for the file/inode/dentry
194 * setup. Returns new descriptor or an error code.
195 */
196int anon_inode_getfd(const char *name, const struct file_operations *fops,
197 void *priv, int flags)
198{
199 int error, fd;
200 struct file *file;
201
202 error = get_unused_fd_flags(flags);
203 if (error < 0)
204 return error;
205 fd = error;
206
207 file = anon_inode_getfile(name, fops, priv, flags);
208 if (IS_ERR(file)) {
209 error = PTR_ERR(file);
210 goto err_put_unused_fd;
211 }
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700212 fd_install(fd, file);
213
Al Viro2030a422008-02-23 06:46:49 -0500214 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700215
216err_put_unused_fd:
217 put_unused_fd(fd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700218 return error;
219}
Avi Kivityd6d28162007-06-28 08:38:16 -0400220EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700221
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700222static int __init anon_inode_init(void)
223{
224 int error;
225
226 error = register_filesystem(&anon_inode_fs_type);
227 if (error)
228 goto err_exit;
229 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
230 if (IS_ERR(anon_inode_mnt)) {
231 error = PTR_ERR(anon_inode_mnt);
232 goto err_unregister_filesystem;
233 }
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700234 return 0;
235
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700236err_unregister_filesystem:
237 unregister_filesystem(&anon_inode_fs_type);
238err_exit:
239 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
240}
241
242fs_initcall(anon_inode_init);
243