Root/fs/anon_inodes.c

1/*
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/cred.h>
12#include <linux/file.h>
13#include <linux/poll.h>
14#include <linux/sched.h>
15#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
37/*
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
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 const struct dentry_operations anon_inodefs_dentry_operations = {
52    .d_dname = anon_inodefs_dname,
53};
54
55/*
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
68/**
69 * anon_inode_getfd - creates a new file instance by hooking it up to an
70 * anonymous inode, and a dentry that describe the "class"
71 * of the file
72 *
73 * @name: [in] name of the "class" of the new file
74 * @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
77 *
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.
80 * All the files created with anon_inode_getfile() will share a single inode,
81 * hence saving memory and avoiding code duplication for the file/inode/dentry
82 * setup. Returns the newly created file* or an error pointer.
83 */
84struct file *anon_inode_getfile(const char *name,
85                const struct file_operations *fops,
86                void *priv, int flags)
87{
88    struct qstr this;
89    struct path path;
90    struct file *file;
91    int error;
92
93    if (IS_ERR(anon_inode_inode))
94        return ERR_PTR(-ENODEV);
95
96    if (fops->owner && !try_module_get(fops->owner))
97        return ERR_PTR(-ENOENT);
98
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;
107    path.dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
108    if (!path.dentry)
109        goto err_module;
110
111    path.mnt = mntget(anon_inode_mnt);
112    /*
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
119    path.dentry->d_op = &anon_inodefs_dentry_operations;
120    d_instantiate(path.dentry, anon_inode_inode);
121
122    error = -ENFILE;
123    file = alloc_file(&path, OPEN_FMODE(flags), fops);
124    if (!file)
125        goto err_dput;
126    file->f_mapping = anon_inode_inode->i_mapping;
127
128    file->f_pos = 0;
129    file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
130    file->f_version = 0;
131    file->private_data = priv;
132
133    return file;
134
135err_dput:
136    path_put(&path);
137err_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    }
175    fd_install(fd, file);
176
177    return fd;
178
179err_put_unused_fd:
180    put_unused_fd(fd);
181    return error;
182}
183EXPORT_SYMBOL_GPL(anon_inode_getfd);
184
185/*
186 * 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.
189 */
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
199    inode->i_mapping->a_ops = &anon_aops;
200
201    /*
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;
209    inode->i_uid = current_fsuid();
210    inode->i_gid = current_fsgid();
211    inode->i_flags |= S_PRIVATE;
212    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
246

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