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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 | /* |
43 | * nop .set_page_dirty method so that people can use .page_mkwrite on |
44 | * anon inodes. |
45 | */ |
46 | static int anon_set_page_dirty(struct page *page) |
47 | { |
48 | return 0; |
49 | }; |
50 | |
51 | static const struct address_space_operations anon_aops = { |
52 | .set_page_dirty = anon_set_page_dirty, |
53 | }; |
54 | |
55 | /* |
56 | * A single inode exists for all anon_inode files. Contrary to pipes, |
57 | * anon_inode inodes have no associated per-instance data, so we need |
58 | * only allocate one of them. |
59 | */ |
60 | static struct inode *anon_inode_mkinode(struct super_block *s) |
61 | { |
62 | struct inode *inode = new_inode_pseudo(s); |
63 | |
64 | if (!inode) |
65 | return ERR_PTR(-ENOMEM); |
66 | |
67 | inode->i_ino = get_next_ino(); |
68 | inode->i_fop = &anon_inode_fops; |
69 | |
70 | inode->i_mapping->a_ops = &anon_aops; |
71 | |
72 | /* |
73 | * Mark the inode dirty from the very beginning, |
74 | * that way it will never be moved to the dirty |
75 | * list because mark_inode_dirty() will think |
76 | * that it already _is_ on the dirty list. |
77 | */ |
78 | inode->i_state = I_DIRTY; |
79 | inode->i_mode = S_IRUSR | S_IWUSR; |
80 | inode->i_uid = current_fsuid(); |
81 | inode->i_gid = current_fsgid(); |
82 | inode->i_flags |= S_PRIVATE; |
83 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; |
84 | return inode; |
85 | } |
86 | |
87 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, |
88 | int flags, const char *dev_name, void *data) |
89 | { |
90 | struct dentry *root; |
91 | root = mount_pseudo(fs_type, "anon_inode:", NULL, |
92 | &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); |
93 | if (!IS_ERR(root)) { |
94 | struct super_block *s = root->d_sb; |
95 | anon_inode_inode = anon_inode_mkinode(s); |
96 | if (IS_ERR(anon_inode_inode)) { |
97 | dput(root); |
98 | deactivate_locked_super(s); |
99 | root = ERR_CAST(anon_inode_inode); |
100 | } |
101 | } |
102 | return root; |
103 | } |
104 | |
105 | static struct file_system_type anon_inode_fs_type = { |
106 | .name = "anon_inodefs", |
107 | .mount = anon_inodefs_mount, |
108 | .kill_sb = kill_anon_super, |
109 | }; |
110 | |
111 | /** |
112 | * anon_inode_getfile - creates a new file instance by hooking it up to an |
113 | * anonymous inode, and a dentry that describe the "class" |
114 | * of the file |
115 | * |
116 | * @name: [in] name of the "class" of the new file |
117 | * @fops: [in] file operations for the new file |
118 | * @priv: [in] private data for the new file (will be file's private_data) |
119 | * @flags: [in] flags |
120 | * |
121 | * Creates a new file by hooking it on a single inode. This is useful for files |
122 | * that do not need to have a full-fledged inode in order to operate correctly. |
123 | * All the files created with anon_inode_getfile() will share a single inode, |
124 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
125 | * setup. Returns the newly created file* or an error pointer. |
126 | */ |
127 | struct file *anon_inode_getfile(const char *name, |
128 | const struct file_operations *fops, |
129 | void *priv, int flags) |
130 | { |
131 | struct qstr this; |
132 | struct path path; |
133 | struct file *file; |
134 | |
135 | if (IS_ERR(anon_inode_inode)) |
136 | return ERR_PTR(-ENODEV); |
137 | |
138 | if (fops->owner && !try_module_get(fops->owner)) |
139 | return ERR_PTR(-ENOENT); |
140 | |
141 | /* |
142 | * Link the inode to a directory entry by creating a unique name |
143 | * using the inode sequence number. |
144 | */ |
145 | file = ERR_PTR(-ENOMEM); |
146 | this.name = name; |
147 | this.len = strlen(name); |
148 | this.hash = 0; |
149 | path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); |
150 | if (!path.dentry) |
151 | goto err_module; |
152 | |
153 | path.mnt = mntget(anon_inode_mnt); |
154 | /* |
155 | * We know the anon_inode inode count is always greater than zero, |
156 | * so ihold() is safe. |
157 | */ |
158 | ihold(anon_inode_inode); |
159 | |
160 | d_instantiate(path.dentry, anon_inode_inode); |
161 | |
162 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
163 | if (IS_ERR(file)) |
164 | goto err_dput; |
165 | file->f_mapping = anon_inode_inode->i_mapping; |
166 | |
167 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
168 | file->private_data = priv; |
169 | |
170 | return file; |
171 | |
172 | err_dput: |
173 | path_put(&path); |
174 | err_module: |
175 | module_put(fops->owner); |
176 | return file; |
177 | } |
178 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
179 | |
180 | /** |
181 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
182 | * anonymous inode, and a dentry that describe the "class" |
183 | * of the file |
184 | * |
185 | * @name: [in] name of the "class" of the new file |
186 | * @fops: [in] file operations for the new file |
187 | * @priv: [in] private data for the new file (will be file's private_data) |
188 | * @flags: [in] flags |
189 | * |
190 | * Creates a new file by hooking it on a single inode. This is useful for files |
191 | * that do not need to have a full-fledged inode in order to operate correctly. |
192 | * All the files created with anon_inode_getfd() will share a single inode, |
193 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
194 | * setup. Returns new descriptor or an error code. |
195 | */ |
196 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
197 | void *priv, int flags) |
198 | { |
199 | int error, fd; |
200 | struct file *file; |
201 | |
202 | error = get_unused_fd_flags(flags); |
203 | if (error < 0) |
204 | return error; |
205 | fd = error; |
206 | |
207 | file = anon_inode_getfile(name, fops, priv, flags); |
208 | if (IS_ERR(file)) { |
209 | error = PTR_ERR(file); |
210 | goto err_put_unused_fd; |
211 | } |
212 | fd_install(fd, file); |
213 | |
214 | return fd; |
215 | |
216 | err_put_unused_fd: |
217 | put_unused_fd(fd); |
218 | return error; |
219 | } |
220 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
221 | |
222 | static int __init anon_inode_init(void) |
223 | { |
224 | int error; |
225 | |
226 | error = register_filesystem(&anon_inode_fs_type); |
227 | if (error) |
228 | goto err_exit; |
229 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
230 | if (IS_ERR(anon_inode_mnt)) { |
231 | error = PTR_ERR(anon_inode_mnt); |
232 | goto err_unregister_filesystem; |
233 | } |
234 | return 0; |
235 | |
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 | |
244 |
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