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
24 static struct vfsmount *anon_inode_mnt __read_mostly;
25 static struct inode *anon_inode_inode;
26 static const struct file_operations anon_inode_fops;
27
28 static 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
36 static 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
46 static 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 };
51 static 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 */
59 static int anon_set_page_dirty(struct page *page)
60 {
61 return 0;
62 };
63
64 static 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 */
84 int 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
143 err_dput:
144 dput(dentry);
145 err_put_unused_fd:
146 put_unused_fd(fd);
147 err_module:
148 module_put(fops->owner);
149 return error;
150 }
151 EXPORT_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 */
158 static 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
183 static 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
203 err_mntput:
204 mntput(anon_inode_mnt);
205 err_unregister_filesystem:
206 unregister_filesystem(&anon_inode_fs_type);
207 err_exit:
208 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
209 }
210
211 fs_initcall(anon_inode_init);
212
213
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