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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 | /* |
30 | * anon_inodefs_dname() is called from d_path(). |
31 | */ |
32 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) |
33 | { |
34 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", |
35 | dentry->d_name.name); |
36 | } |
37 | |
38 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
39 | .d_dname = anon_inodefs_dname, |
40 | }; |
41 | |
42 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, |
43 | int flags, const char *dev_name, void *data) |
44 | { |
45 | return mount_pseudo(fs_type, "anon_inode:", NULL, |
46 | &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); |
47 | } |
48 | |
49 | static struct file_system_type anon_inode_fs_type = { |
50 | .name = "anon_inodefs", |
51 | .mount = anon_inodefs_mount, |
52 | .kill_sb = kill_anon_super, |
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_getfile - 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_getfile() will share a single inode, |
81 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
82 | * setup. Returns the newly created file* or an error pointer. |
83 | */ |
84 | struct file *anon_inode_getfile(const char *name, |
85 | const struct file_operations *fops, |
86 | void *priv, int flags) |
87 | { |
88 | struct qstr this; |
89 | struct path path; |
90 | struct file *file; |
91 | int error; |
92 | |
93 | if (IS_ERR(anon_inode_inode)) |
94 | return ERR_PTR(-ENODEV); |
95 | |
96 | if (fops->owner && !try_module_get(fops->owner)) |
97 | return ERR_PTR(-ENOENT); |
98 | |
99 | /* |
100 | * Link the inode to a directory entry by creating a unique name |
101 | * using the inode sequence number. |
102 | */ |
103 | error = -ENOMEM; |
104 | this.name = name; |
105 | this.len = strlen(name); |
106 | this.hash = 0; |
107 | path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); |
108 | if (!path.dentry) |
109 | goto err_module; |
110 | |
111 | path.mnt = mntget(anon_inode_mnt); |
112 | /* |
113 | * We know the anon_inode inode count is always greater than zero, |
114 | * so ihold() is safe. |
115 | */ |
116 | ihold(anon_inode_inode); |
117 | |
118 | d_instantiate(path.dentry, anon_inode_inode); |
119 | |
120 | error = -ENFILE; |
121 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
122 | if (!file) |
123 | goto err_dput; |
124 | file->f_mapping = anon_inode_inode->i_mapping; |
125 | |
126 | file->f_pos = 0; |
127 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
128 | file->f_version = 0; |
129 | file->private_data = priv; |
130 | |
131 | return file; |
132 | |
133 | err_dput: |
134 | path_put(&path); |
135 | err_module: |
136 | module_put(fops->owner); |
137 | return ERR_PTR(error); |
138 | } |
139 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
140 | |
141 | /** |
142 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
143 | * anonymous inode, and a dentry that describe the "class" |
144 | * of the file |
145 | * |
146 | * @name: [in] name of the "class" of the new file |
147 | * @fops: [in] file operations for the new file |
148 | * @priv: [in] private data for the new file (will be file's private_data) |
149 | * @flags: [in] flags |
150 | * |
151 | * Creates a new file by hooking it on a single inode. This is useful for files |
152 | * that do not need to have a full-fledged inode in order to operate correctly. |
153 | * All the files created with anon_inode_getfd() will share a single inode, |
154 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
155 | * setup. Returns new descriptor or an error code. |
156 | */ |
157 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
158 | void *priv, int flags) |
159 | { |
160 | int error, fd; |
161 | struct file *file; |
162 | |
163 | error = get_unused_fd_flags(flags); |
164 | if (error < 0) |
165 | return error; |
166 | fd = error; |
167 | |
168 | file = anon_inode_getfile(name, fops, priv, flags); |
169 | if (IS_ERR(file)) { |
170 | error = PTR_ERR(file); |
171 | goto err_put_unused_fd; |
172 | } |
173 | fd_install(fd, file); |
174 | |
175 | return fd; |
176 | |
177 | err_put_unused_fd: |
178 | put_unused_fd(fd); |
179 | return error; |
180 | } |
181 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
182 | |
183 | /* |
184 | * A single inode exists for all anon_inode files. Contrary to pipes, |
185 | * anon_inode inodes have no associated per-instance data, so we need |
186 | * only allocate one of them. |
187 | */ |
188 | static struct inode *anon_inode_mkinode(void) |
189 | { |
190 | struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); |
191 | |
192 | if (!inode) |
193 | return ERR_PTR(-ENOMEM); |
194 | |
195 | inode->i_ino = get_next_ino(); |
196 | inode->i_fop = &anon_inode_fops; |
197 | |
198 | inode->i_mapping->a_ops = &anon_aops; |
199 | |
200 | /* |
201 | * Mark the inode dirty from the very beginning, |
202 | * that way it will never be moved to the dirty |
203 | * list because mark_inode_dirty() will think |
204 | * that it already _is_ on the dirty list. |
205 | */ |
206 | inode->i_state = I_DIRTY; |
207 | inode->i_mode = S_IRUSR | S_IWUSR; |
208 | inode->i_uid = current_fsuid(); |
209 | inode->i_gid = current_fsgid(); |
210 | inode->i_flags |= S_PRIVATE; |
211 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; |
212 | return inode; |
213 | } |
214 | |
215 | static int __init anon_inode_init(void) |
216 | { |
217 | int error; |
218 | |
219 | error = register_filesystem(&anon_inode_fs_type); |
220 | if (error) |
221 | goto err_exit; |
222 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
223 | if (IS_ERR(anon_inode_mnt)) { |
224 | error = PTR_ERR(anon_inode_mnt); |
225 | goto err_unregister_filesystem; |
226 | } |
227 | anon_inode_inode = anon_inode_mkinode(); |
228 | if (IS_ERR(anon_inode_inode)) { |
229 | error = PTR_ERR(anon_inode_inode); |
230 | goto err_mntput; |
231 | } |
232 | |
233 | return 0; |
234 | |
235 | err_mntput: |
236 | mntput(anon_inode_mnt); |
237 | err_unregister_filesystem: |
238 | unregister_filesystem(&anon_inode_fs_type); |
239 | err_exit: |
240 | panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); |
241 | } |
242 | |
243 | fs_initcall(anon_inode_init); |
244 | |
245 |
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