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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 | ||
25 | static struct vfsmount *anon_inode_mnt __read_mostly; | |
26 | static struct inode *anon_inode_inode; | |
27 | static const struct file_operations anon_inode_fops; | |
28 | ||
29 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, | |
30 | int flags, const char *dev_name, void *data) | |
31 | { | |
32 | return mount_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC); | |
33 | } | |
34 | ||
35 | /* | |
36 | * anon_inodefs_dname() is called from d_path(). | |
37 | */ | |
38 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) | |
39 | { | |
40 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", | |
41 | dentry->d_name.name); | |
42 | } | |
43 | ||
44 | static struct file_system_type anon_inode_fs_type = { | |
45 | .name = "anon_inodefs", | |
46 | .mount = anon_inodefs_mount, | |
47 | .kill_sb = kill_anon_super, | |
48 | }; | |
49 | static const struct dentry_operations anon_inodefs_dentry_operations = { | |
50 | .d_dname = anon_inodefs_dname, | |
51 | }; | |
52 | ||
53 | /* | |
54 | * nop .set_page_dirty method so that people can use .page_mkwrite on | |
55 | * anon inodes. | |
56 | */ | |
57 | static int anon_set_page_dirty(struct page *page) | |
58 | { | |
59 | return 0; | |
60 | }; | |
61 | ||
62 | static const struct address_space_operations anon_aops = { | |
63 | .set_page_dirty = anon_set_page_dirty, | |
64 | }; | |
65 | ||
66 | /** | |
67 | * anon_inode_getfd - creates a new file instance by hooking it up to an | |
68 | * anonymous inode, and a dentry that describe the "class" | |
69 | * of the file | |
70 | * | |
71 | * @name: [in] name of the "class" of the new file | |
72 | * @fops: [in] file operations for the new file | |
73 | * @priv: [in] private data for the new file (will be file's private_data) | |
74 | * @flags: [in] flags | |
75 | * | |
76 | * Creates a new file by hooking it on a single inode. This is useful for files | |
77 | * that do not need to have a full-fledged inode in order to operate correctly. | |
78 | * All the files created with anon_inode_getfile() will share a single inode, | |
79 | * hence saving memory and avoiding code duplication for the file/inode/dentry | |
80 | * setup. Returns the newly created file* or an error pointer. | |
81 | */ | |
82 | struct file *anon_inode_getfile(const char *name, | |
83 | const struct file_operations *fops, | |
84 | void *priv, int flags) | |
85 | { | |
86 | struct qstr this; | |
87 | struct path path; | |
88 | struct file *file; | |
89 | int error; | |
90 | ||
91 | if (IS_ERR(anon_inode_inode)) | |
92 | return ERR_PTR(-ENODEV); | |
93 | ||
94 | if (fops->owner && !try_module_get(fops->owner)) | |
95 | return ERR_PTR(-ENOENT); | |
96 | ||
97 | /* | |
98 | * Link the inode to a directory entry by creating a unique name | |
99 | * using the inode sequence number. | |
100 | */ | |
101 | error = -ENOMEM; | |
102 | this.name = name; | |
103 | this.len = strlen(name); | |
104 | this.hash = 0; | |
105 | path.dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); | |
106 | if (!path.dentry) | |
107 | goto err_module; | |
108 | ||
109 | path.mnt = mntget(anon_inode_mnt); | |
110 | /* | |
111 | * We know the anon_inode inode count is always greater than zero, | |
112 | * so ihold() is safe. | |
113 | */ | |
114 | ihold(anon_inode_inode); | |
115 | ||
116 | path.dentry->d_op = &anon_inodefs_dentry_operations; | |
117 | d_instantiate(path.dentry, anon_inode_inode); | |
118 | ||
119 | error = -ENFILE; | |
120 | file = alloc_file(&path, OPEN_FMODE(flags), fops); | |
121 | if (!file) | |
122 | goto err_dput; | |
123 | file->f_mapping = anon_inode_inode->i_mapping; | |
124 | ||
125 | file->f_pos = 0; | |
126 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); | |
127 | file->f_version = 0; | |
128 | file->private_data = priv; | |
129 | ||
130 | return file; | |
131 | ||
132 | err_dput: | |
133 | path_put(&path); | |
134 | err_module: | |
135 | module_put(fops->owner); | |
136 | return ERR_PTR(error); | |
137 | } | |
138 | EXPORT_SYMBOL_GPL(anon_inode_getfile); | |
139 | ||
140 | /** | |
141 | * anon_inode_getfd - creates a new file instance by hooking it up to an | |
142 | * anonymous inode, and a dentry that describe the "class" | |
143 | * of the file | |
144 | * | |
145 | * @name: [in] name of the "class" of the new file | |
146 | * @fops: [in] file operations for the new file | |
147 | * @priv: [in] private data for the new file (will be file's private_data) | |
148 | * @flags: [in] flags | |
149 | * | |
150 | * Creates a new file by hooking it on a single inode. This is useful for files | |
151 | * that do not need to have a full-fledged inode in order to operate correctly. | |
152 | * All the files created with anon_inode_getfd() will share a single inode, | |
153 | * hence saving memory and avoiding code duplication for the file/inode/dentry | |
154 | * setup. Returns new descriptor or an error code. | |
155 | */ | |
156 | int anon_inode_getfd(const char *name, const struct file_operations *fops, | |
157 | void *priv, int flags) | |
158 | { | |
159 | int error, fd; | |
160 | struct file *file; | |
161 | ||
162 | error = get_unused_fd_flags(flags); | |
163 | if (error < 0) | |
164 | return error; | |
165 | fd = error; | |
166 | ||
167 | file = anon_inode_getfile(name, fops, priv, flags); | |
168 | if (IS_ERR(file)) { | |
169 | error = PTR_ERR(file); | |
170 | goto err_put_unused_fd; | |
171 | } | |
172 | fd_install(fd, file); | |
173 | ||
174 | return fd; | |
175 | ||
176 | err_put_unused_fd: | |
177 | put_unused_fd(fd); | |
178 | return error; | |
179 | } | |
180 | EXPORT_SYMBOL_GPL(anon_inode_getfd); | |
181 | ||
182 | /* | |
183 | * A single inode exists for all anon_inode files. Contrary to pipes, | |
184 | * anon_inode inodes have no associated per-instance data, so we need | |
185 | * only allocate one of them. | |
186 | */ | |
187 | static struct inode *anon_inode_mkinode(void) | |
188 | { | |
189 | struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); | |
190 | ||
191 | if (!inode) | |
192 | return ERR_PTR(-ENOMEM); | |
193 | ||
194 | inode->i_ino = get_next_ino(); | |
195 | inode->i_fop = &anon_inode_fops; | |
196 | ||
197 | inode->i_mapping->a_ops = &anon_aops; | |
198 | ||
199 | /* | |
200 | * Mark the inode dirty from the very beginning, | |
201 | * that way it will never be moved to the dirty | |
202 | * list because mark_inode_dirty() will think | |
203 | * that it already _is_ on the dirty list. | |
204 | */ | |
205 | inode->i_state = I_DIRTY; | |
206 | inode->i_mode = S_IRUSR | S_IWUSR; | |
207 | inode->i_uid = current_fsuid(); | |
208 | inode->i_gid = current_fsgid(); | |
209 | inode->i_flags |= S_PRIVATE; | |
210 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; | |
211 | return inode; | |
212 | } | |
213 | ||
214 | static int __init anon_inode_init(void) | |
215 | { | |
216 | int error; | |
217 | ||
218 | error = register_filesystem(&anon_inode_fs_type); | |
219 | if (error) | |
220 | goto err_exit; | |
221 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); | |
222 | if (IS_ERR(anon_inode_mnt)) { | |
223 | error = PTR_ERR(anon_inode_mnt); | |
224 | goto err_unregister_filesystem; | |
225 | } | |
226 | anon_inode_inode = anon_inode_mkinode(); | |
227 | if (IS_ERR(anon_inode_inode)) { | |
228 | error = PTR_ERR(anon_inode_inode); | |
229 | goto err_mntput; | |
230 | } | |
231 | ||
232 | return 0; | |
233 | ||
234 | err_mntput: | |
235 | mntput(anon_inode_mnt); | |
236 | err_unregister_filesystem: | |
237 | unregister_filesystem(&anon_inode_fs_type); | |
238 | err_exit: | |
239 | panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); | |
240 | } | |
241 | ||
242 | fs_initcall(anon_inode_init); | |
243 |