Commit | Line | Data |
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5dc8bf81 DL |
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 | }; | |
3ba13d17 | 51 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
5dc8bf81 DL |
52 | .d_delete = anon_inodefs_delete_dentry, |
53 | }; | |
54 | ||
d3a9262e PZ |
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 | ||
5dc8bf81 | 68 | /** |
4b4e5a14 | 69 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
5dc8bf81 DL |
70 | * anonymous inode, and a dentry that describe the "class" |
71 | * of the file | |
72 | * | |
5dc8bf81 | 73 | * @name: [in] name of the "class" of the new file |
7d9dbca3 UD |
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 | |
5dc8bf81 DL |
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. | |
4b4e5a14 | 80 | * All the files created with anon_inode_getfd() will share a single inode, |
5dc8bf81 | 81 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
2030a42c | 82 | * setup. Returns new descriptor or -error. |
5dc8bf81 | 83 | */ |
2030a42c | 84 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
7d9dbca3 | 85 | void *priv, int flags) |
5dc8bf81 DL |
86 | { |
87 | struct qstr this; | |
88 | struct dentry *dentry; | |
5dc8bf81 DL |
89 | struct file *file; |
90 | int error, fd; | |
91 | ||
92 | if (IS_ERR(anon_inode_inode)) | |
93 | return -ENODEV; | |
5dc8bf81 | 94 | |
e3a2a0d4 CB |
95 | if (fops->owner && !try_module_get(fops->owner)) |
96 | return -ENOENT; | |
97 | ||
7d9dbca3 | 98 | error = get_unused_fd_flags(flags); |
5dc8bf81 | 99 | if (error < 0) |
e3a2a0d4 | 100 | goto err_module; |
5dc8bf81 DL |
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; | |
96fdc72d DL |
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 | ||
5dc8bf81 DL |
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; | |
96fdc72d | 125 | d_instantiate(dentry, anon_inode_inode); |
5dc8bf81 | 126 | |
430e285e DH |
127 | error = -ENFILE; |
128 | file = alloc_file(anon_inode_mnt, dentry, | |
129 | FMODE_READ | FMODE_WRITE, fops); | |
130 | if (!file) | |
131 | goto err_dput; | |
96fdc72d | 132 | file->f_mapping = anon_inode_inode->i_mapping; |
5dc8bf81 DL |
133 | |
134 | file->f_pos = 0; | |
99829b83 | 135 | file->f_flags = O_RDWR | (flags & O_NONBLOCK); |
5dc8bf81 DL |
136 | file->f_version = 0; |
137 | file->private_data = priv; | |
138 | ||
139 | fd_install(fd, file); | |
140 | ||
2030a42c | 141 | return fd; |
5dc8bf81 | 142 | |
430e285e DH |
143 | err_dput: |
144 | dput(dentry); | |
5dc8bf81 DL |
145 | err_put_unused_fd: |
146 | put_unused_fd(fd); | |
e3a2a0d4 CB |
147 | err_module: |
148 | module_put(fops->owner); | |
5dc8bf81 DL |
149 | return error; |
150 | } | |
d6d28168 | 151 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
5dc8bf81 DL |
152 | |
153 | /* | |
4b4e5a14 BF |
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. | |
5dc8bf81 DL |
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 | ||
d3a9262e PZ |
167 | inode->i_mapping->a_ops = &anon_aops; |
168 | ||
5dc8bf81 DL |
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; | |
da9592ed DH |
177 | inode->i_uid = current_fsuid(); |
178 | inode->i_gid = current_fsgid(); | |
5dc8bf81 DL |
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 |