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/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};
51static const struct dentry_operations anon_inodefs_dentry_operations = {
52    .d_delete = anon_inodefs_delete_dentry,
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_getfd() will share a single inode,
81 * hence saving memory and avoiding code duplication for the file/inode/dentry
82 * setup. Returns new descriptor or -error.
83 */
84int anon_inode_getfd(const char *name, const struct file_operations *fops,
85             void *priv, int flags)
86{
87    struct qstr this;
88    struct dentry *dentry;
89    struct file *file;
90    int error, fd;
91
92    if (IS_ERR(anon_inode_inode))
93        return -ENODEV;
94
95    if (fops->owner && !try_module_get(fops->owner))
96        return -ENOENT;
97
98    error = get_unused_fd_flags(flags);
99    if (error < 0)
100        goto err_module;
101    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;
114
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
122    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;
125    d_instantiate(dentry, anon_inode_inode);
126
127    error = -ENFILE;
128    file = alloc_file(anon_inode_mnt, dentry,
129              FMODE_READ | FMODE_WRITE, fops);
130    if (!file)
131        goto err_dput;
132    file->f_mapping = anon_inode_inode->i_mapping;
133
134    file->f_pos = 0;
135    file->f_flags = O_RDWR | (flags & O_NONBLOCK);
136    file->f_version = 0;
137    file->private_data = priv;
138
139    fd_install(fd, file);
140
141    return fd;
142
143err_dput:
144    dput(dentry);
145err_put_unused_fd:
146    put_unused_fd(fd);
147err_module:
148    module_put(fops->owner);
149    return error;
150}
151EXPORT_SYMBOL_GPL(anon_inode_getfd);
152
153/*
154 * 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.
157 */
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
167    inode->i_mapping->a_ops = &anon_aops;
168
169    /*
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;
177    inode->i_uid = current_fsuid();
178    inode->i_gid = current_fsgid();
179    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
213

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