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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/slab.h>
16#include <linux/init.h>
17#include <linux/fs.h>
18#include <linux/mount.h>
19#include <linux/module.h>
20#include <linux/kernel.h>
21#include <linux/magic.h>
22#include <linux/anon_inodes.h>
23
24#include <asm/uaccess.h>
25
26static struct vfsmount *anon_inode_mnt __read_mostly;
27static struct inode *anon_inode_inode;
28static const struct file_operations anon_inode_fops;
29
30static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
31 const char *dev_name, void *data,
32 struct vfsmount *mnt)
33{
34 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
35 mnt);
36}
37
38static int anon_inodefs_delete_dentry(struct dentry *dentry)
39{
40 /*
41 * We faked vfs to believe the dentry was hashed when we created it.
42 * Now we restore the flag so that dput() will work correctly.
43 */
44 dentry->d_flags |= DCACHE_UNHASHED;
45 return 1;
46}
47
48static struct file_system_type anon_inode_fs_type = {
49 .name = "anon_inodefs",
50 .get_sb = anon_inodefs_get_sb,
51 .kill_sb = kill_anon_super,
52};
Al Viro3ba13d12009-02-20 06:02:22 +000053static const struct dentry_operations anon_inodefs_dentry_operations = {
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070054 .d_delete = anon_inodefs_delete_dentry,
55};
56
Peter Zijlstrad3a92622009-06-18 12:54:00 +020057/*
58 * nop .set_page_dirty method so that people can use .page_mkwrite on
59 * anon inodes.
60 */
61static int anon_set_page_dirty(struct page *page)
62{
63 return 0;
64};
65
66static const struct address_space_operations anon_aops = {
67 .set_page_dirty = anon_set_page_dirty,
68};
69
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070070/**
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -070071 * anon_inode_getfd - creates a new file instance by hooking it up to an
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070072 * anonymous inode, and a dentry that describe the "class"
73 * of the file
74 *
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070075 * @name: [in] name of the "class" of the new file
Ulrich Drepper7d9dbca2008-07-23 21:29:22 -070076 * @fops: [in] file operations for the new file
77 * @priv: [in] private data for the new file (will be file's private_data)
78 * @flags: [in] flags
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070079 *
80 * Creates a new file by hooking it on a single inode. This is useful for files
81 * that do not need to have a full-fledged inode in order to operate correctly.
Davide Libenzi562787a2009-09-22 16:43:57 -070082 * All the files created with anon_inode_getfile() will share a single inode,
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070083 * hence saving memory and avoiding code duplication for the file/inode/dentry
Davide Libenzi562787a2009-09-22 16:43:57 -070084 * setup. Returns the newly created file* or an error pointer.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070085 */
Davide Libenzi562787a2009-09-22 16:43:57 -070086struct file *anon_inode_getfile(const char *name,
87 const struct file_operations *fops,
88 void *priv, int flags)
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070089{
90 struct qstr this;
91 struct dentry *dentry;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070092 struct file *file;
Davide Libenzi562787a2009-09-22 16:43:57 -070093 int error;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070094
95 if (IS_ERR(anon_inode_inode))
Davide Libenzi562787a2009-09-22 16:43:57 -070096 return ERR_PTR(-ENODEV);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -070097
Christian Borntraegere3a2a0d2008-12-02 11:16:03 +010098 if (fops->owner && !try_module_get(fops->owner))
Davide Libenzi562787a2009-09-22 16:43:57 -070099 return ERR_PTR(-ENOENT);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700100
101 /*
102 * Link the inode to a directory entry by creating a unique name
103 * using the inode sequence number.
104 */
105 error = -ENOMEM;
106 this.name = name;
107 this.len = strlen(name);
108 this.hash = 0;
109 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
110 if (!dentry)
Davide Libenzi562787a2009-09-22 16:43:57 -0700111 goto err_module;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700112
113 /*
114 * We know the anon_inode inode count is always greater than zero,
115 * so we can avoid doing an igrab() and we can use an open-coded
116 * atomic_inc().
117 */
118 atomic_inc(&anon_inode_inode->i_count);
119
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700120 dentry->d_op = &anon_inodefs_dentry_operations;
121 /* Do not publish this dentry inside the global dentry hash table */
122 dentry->d_flags &= ~DCACHE_UNHASHED;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700123 d_instantiate(dentry, anon_inode_inode);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700124
Dave Hansen430e2852008-02-15 14:37:26 -0800125 error = -ENFILE;
126 file = alloc_file(anon_inode_mnt, dentry,
127 FMODE_READ | FMODE_WRITE, fops);
128 if (!file)
129 goto err_dput;
Davide Libenzi96fdc722007-10-16 23:30:19 -0700130 file->f_mapping = anon_inode_inode->i_mapping;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700131
132 file->f_pos = 0;
Ulrich Drepper99829b82008-07-23 21:29:33 -0700133 file->f_flags = O_RDWR | (flags & O_NONBLOCK);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700134 file->f_version = 0;
135 file->private_data = priv;
136
Davide Libenzi562787a2009-09-22 16:43:57 -0700137 return file;
138
139err_dput:
140 dput(dentry);
141err_module:
142 module_put(fops->owner);
143 return ERR_PTR(error);
144}
145EXPORT_SYMBOL_GPL(anon_inode_getfile);
146
147/**
148 * anon_inode_getfd - creates a new file instance by hooking it up to an
149 * anonymous inode, and a dentry that describe the "class"
150 * of the file
151 *
152 * @name: [in] name of the "class" of the new file
153 * @fops: [in] file operations for the new file
154 * @priv: [in] private data for the new file (will be file's private_data)
155 * @flags: [in] flags
156 *
157 * Creates a new file by hooking it on a single inode. This is useful for files
158 * that do not need to have a full-fledged inode in order to operate correctly.
159 * All the files created with anon_inode_getfd() will share a single inode,
160 * hence saving memory and avoiding code duplication for the file/inode/dentry
161 * setup. Returns new descriptor or an error code.
162 */
163int anon_inode_getfd(const char *name, const struct file_operations *fops,
164 void *priv, int flags)
165{
166 int error, fd;
167 struct file *file;
168
169 error = get_unused_fd_flags(flags);
170 if (error < 0)
171 return error;
172 fd = error;
173
174 file = anon_inode_getfile(name, fops, priv, flags);
175 if (IS_ERR(file)) {
176 error = PTR_ERR(file);
177 goto err_put_unused_fd;
178 }
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700179 fd_install(fd, file);
180
Al Viro2030a422008-02-23 06:46:49 -0500181 return fd;
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700182
183err_put_unused_fd:
184 put_unused_fd(fd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700185 return error;
186}
Avi Kivityd6d28162007-06-28 08:38:16 -0400187EXPORT_SYMBOL_GPL(anon_inode_getfd);
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700188
189/*
J. Bruce Fields4b4e5a12007-07-15 23:41:53 -0700190 * A single inode exists for all anon_inode files. Contrary to pipes,
191 * anon_inode inodes have no associated per-instance data, so we need
192 * only allocate one of them.
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700193 */
194static struct inode *anon_inode_mkinode(void)
195{
196 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
197
198 if (!inode)
199 return ERR_PTR(-ENOMEM);
200
201 inode->i_fop = &anon_inode_fops;
202
Peter Zijlstrad3a92622009-06-18 12:54:00 +0200203 inode->i_mapping->a_ops = &anon_aops;
204
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700205 /*
206 * Mark the inode dirty from the very beginning,
207 * that way it will never be moved to the dirty
208 * list because mark_inode_dirty() will think
209 * that it already _is_ on the dirty list.
210 */
211 inode->i_state = I_DIRTY;
212 inode->i_mode = S_IRUSR | S_IWUSR;
David Howellsda9592e2008-11-14 10:39:05 +1100213 inode->i_uid = current_fsuid();
214 inode->i_gid = current_fsgid();
Davide Libenzi5dc8bf82007-05-10 22:23:11 -0700215 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
216 return inode;
217}
218
219static int __init anon_inode_init(void)
220{
221 int error;
222
223 error = register_filesystem(&anon_inode_fs_type);
224 if (error)
225 goto err_exit;
226 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
227 if (IS_ERR(anon_inode_mnt)) {
228 error = PTR_ERR(anon_inode_mnt);
229 goto err_unregister_filesystem;
230 }
231 anon_inode_inode = anon_inode_mkinode();
232 if (IS_ERR(anon_inode_inode)) {
233 error = PTR_ERR(anon_inode_inode);
234 goto err_mntput;
235 }
236
237 return 0;
238
239err_mntput:
240 mntput(anon_inode_mnt);
241err_unregister_filesystem:
242 unregister_filesystem(&anon_inode_fs_type);
243err_exit:
244 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
245}
246
247fs_initcall(anon_inode_init);
248