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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 int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags, |
30 | const char *dev_name, void *data, |
31 | struct vfsmount *mnt) |
32 | { |
33 | return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC, |
34 | mnt); |
35 | } |
36 | |
37 | /* |
38 | * anon_inodefs_dname() is called from d_path(). |
39 | */ |
40 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) |
41 | { |
42 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", |
43 | dentry->d_name.name); |
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_dname = anon_inodefs_dname, |
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_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(anon_inode_mnt->mnt_sb->s_root, &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 we can avoid doing an igrab() and we can use an open-coded |
115 | * atomic_inc(). |
116 | */ |
117 | atomic_inc(&anon_inode_inode->i_count); |
118 | |
119 | path.dentry->d_op = &anon_inodefs_dentry_operations; |
120 | d_instantiate(path.dentry, anon_inode_inode); |
121 | |
122 | error = -ENFILE; |
123 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
124 | if (!file) |
125 | goto err_dput; |
126 | file->f_mapping = anon_inode_inode->i_mapping; |
127 | |
128 | file->f_pos = 0; |
129 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
130 | file->f_version = 0; |
131 | file->private_data = priv; |
132 | |
133 | return file; |
134 | |
135 | err_dput: |
136 | path_put(&path); |
137 | err_module: |
138 | module_put(fops->owner); |
139 | return ERR_PTR(error); |
140 | } |
141 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
142 | |
143 | /** |
144 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
145 | * anonymous inode, and a dentry that describe the "class" |
146 | * of the file |
147 | * |
148 | * @name: [in] name of the "class" of the new file |
149 | * @fops: [in] file operations for the new file |
150 | * @priv: [in] private data for the new file (will be file's private_data) |
151 | * @flags: [in] flags |
152 | * |
153 | * Creates a new file by hooking it on a single inode. This is useful for files |
154 | * that do not need to have a full-fledged inode in order to operate correctly. |
155 | * All the files created with anon_inode_getfd() will share a single inode, |
156 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
157 | * setup. Returns new descriptor or an error code. |
158 | */ |
159 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
160 | void *priv, int flags) |
161 | { |
162 | int error, fd; |
163 | struct file *file; |
164 | |
165 | error = get_unused_fd_flags(flags); |
166 | if (error < 0) |
167 | return error; |
168 | fd = error; |
169 | |
170 | file = anon_inode_getfile(name, fops, priv, flags); |
171 | if (IS_ERR(file)) { |
172 | error = PTR_ERR(file); |
173 | goto err_put_unused_fd; |
174 | } |
175 | fd_install(fd, file); |
176 | |
177 | return fd; |
178 | |
179 | err_put_unused_fd: |
180 | put_unused_fd(fd); |
181 | return error; |
182 | } |
183 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
184 | |
185 | /* |
186 | * A single inode exists for all anon_inode files. Contrary to pipes, |
187 | * anon_inode inodes have no associated per-instance data, so we need |
188 | * only allocate one of them. |
189 | */ |
190 | static struct inode *anon_inode_mkinode(void) |
191 | { |
192 | struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); |
193 | |
194 | if (!inode) |
195 | return ERR_PTR(-ENOMEM); |
196 | |
197 | inode->i_fop = &anon_inode_fops; |
198 | |
199 | inode->i_mapping->a_ops = &anon_aops; |
200 | |
201 | /* |
202 | * Mark the inode dirty from the very beginning, |
203 | * that way it will never be moved to the dirty |
204 | * list because mark_inode_dirty() will think |
205 | * that it already _is_ on the dirty list. |
206 | */ |
207 | inode->i_state = I_DIRTY; |
208 | inode->i_mode = S_IRUSR | S_IWUSR; |
209 | inode->i_uid = current_fsuid(); |
210 | inode->i_gid = current_fsgid(); |
211 | inode->i_flags |= S_PRIVATE; |
212 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; |
213 | return inode; |
214 | } |
215 | |
216 | static int __init anon_inode_init(void) |
217 | { |
218 | int error; |
219 | |
220 | error = register_filesystem(&anon_inode_fs_type); |
221 | if (error) |
222 | goto err_exit; |
223 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
224 | if (IS_ERR(anon_inode_mnt)) { |
225 | error = PTR_ERR(anon_inode_mnt); |
226 | goto err_unregister_filesystem; |
227 | } |
228 | anon_inode_inode = anon_inode_mkinode(); |
229 | if (IS_ERR(anon_inode_inode)) { |
230 | error = PTR_ERR(anon_inode_inode); |
231 | goto err_mntput; |
232 | } |
233 | |
234 | return 0; |
235 | |
236 | err_mntput: |
237 | mntput(anon_inode_mnt); |
238 | err_unregister_filesystem: |
239 | unregister_filesystem(&anon_inode_fs_type); |
240 | err_exit: |
241 | panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); |
242 | } |
243 | |
244 | fs_initcall(anon_inode_init); |
245 | |
246 |
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