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-rw-r--r--fs/anon_inodes.c200
1 files changed, 200 insertions, 0 deletions
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
new file mode 100644
index 000000000000..40fe3a3222e4
--- /dev/null
+++ b/fs/anon_inodes.c
@@ -0,0 +1,200 @@
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 struct dentry_operations anon_inodefs_dentry_operations = {
52 .d_delete = anon_inodefs_delete_dentry,
53};
54
55/**
56 * anon_inode_getfd - creates a new file instance by hooking it up to and
57 * anonymous inode, and a dentry that describe the "class"
58 * of the file
59 *
60 * @pfd: [out] pointer to the file descriptor
61 * @dpinode: [out] pointer to the inode
62 * @pfile: [out] pointer to the file struct
63 * @name: [in] name of the "class" of the new file
64 * @fops [in] file operations for the new file
65 * @priv [in] private data for the new file (will be file's private_data)
66 *
67 * Creates a new file by hooking it on a single inode. This is useful for files
68 * that do not need to have a full-fledged inode in order to operate correctly.
69 * All the files created with anon_inode_getfd() will share a single inode, by
70 * hence saving memory and avoiding code duplication for the file/inode/dentry
71 * setup.
72 */
73int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
74 const char *name, const struct file_operations *fops,
75 void *priv)
76{
77 struct qstr this;
78 struct dentry *dentry;
79 struct inode *inode;
80 struct file *file;
81 int error, fd;
82
83 if (IS_ERR(anon_inode_inode))
84 return -ENODEV;
85 file = get_empty_filp();
86 if (!file)
87 return -ENFILE;
88
89 inode = igrab(anon_inode_inode);
90 if (IS_ERR(inode)) {
91 error = PTR_ERR(inode);
92 goto err_put_filp;
93 }
94
95 error = get_unused_fd();
96 if (error < 0)
97 goto err_iput;
98 fd = error;
99
100 /*
101 * Link the inode to a directory entry by creating a unique name
102 * using the inode sequence number.
103 */
104 error = -ENOMEM;
105 this.name = name;
106 this.len = strlen(name);
107 this.hash = 0;
108 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
109 if (!dentry)
110 goto err_put_unused_fd;
111 dentry->d_op = &anon_inodefs_dentry_operations;
112 /* Do not publish this dentry inside the global dentry hash table */
113 dentry->d_flags &= ~DCACHE_UNHASHED;
114 d_instantiate(dentry, inode);
115
116 file->f_path.mnt = mntget(anon_inode_mnt);
117 file->f_path.dentry = dentry;
118 file->f_mapping = inode->i_mapping;
119
120 file->f_pos = 0;
121 file->f_flags = O_RDWR;
122 file->f_op = fops;
123 file->f_mode = FMODE_READ | FMODE_WRITE;
124 file->f_version = 0;
125 file->private_data = priv;
126
127 fd_install(fd, file);
128
129 *pfd = fd;
130 *pinode = inode;
131 *pfile = file;
132 return 0;
133
134err_put_unused_fd:
135 put_unused_fd(fd);
136err_iput:
137 iput(inode);
138err_put_filp:
139 put_filp(file);
140 return error;
141}
142
143/*
144 * A single inode exist for all anon_inode files. Contrary to pipes,
145 * anon_inode inodes has no per-instance data associated, so we can avoid
146 * the allocation of multiple of them.
147 */
148static struct inode *anon_inode_mkinode(void)
149{
150 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
151
152 if (!inode)
153 return ERR_PTR(-ENOMEM);
154
155 inode->i_fop = &anon_inode_fops;
156
157 /*
158 * Mark the inode dirty from the very beginning,
159 * that way it will never be moved to the dirty
160 * list because mark_inode_dirty() will think
161 * that it already _is_ on the dirty list.
162 */
163 inode->i_state = I_DIRTY;
164 inode->i_mode = S_IRUSR | S_IWUSR;
165 inode->i_uid = current->fsuid;
166 inode->i_gid = current->fsgid;
167 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
168 return inode;
169}
170
171static int __init anon_inode_init(void)
172{
173 int error;
174
175 error = register_filesystem(&anon_inode_fs_type);
176 if (error)
177 goto err_exit;
178 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
179 if (IS_ERR(anon_inode_mnt)) {
180 error = PTR_ERR(anon_inode_mnt);
181 goto err_unregister_filesystem;
182 }
183 anon_inode_inode = anon_inode_mkinode();
184 if (IS_ERR(anon_inode_inode)) {
185 error = PTR_ERR(anon_inode_inode);
186 goto err_mntput;
187 }
188
189 return 0;
190
191err_mntput:
192 mntput(anon_inode_mnt);
193err_unregister_filesystem:
194 unregister_filesystem(&anon_inode_fs_type);
195err_exit:
196 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
197}
198
199fs_initcall(anon_inode_init);
200
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