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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/slab.h> |
16 | #include <linux/init.h> |
17 | #include <linux/fs.h> |
18 | #include <linux/mount.h> |
19 | #include <linux/module.h> |
20 | #include <linux/kernel.h> |
21 | #include <linux/magic.h> |
22 | #include <linux/anon_inodes.h> |
23 | |
24 | #include <asm/uaccess.h> |
25 | |
26 | static struct vfsmount *anon_inode_mnt __read_mostly; |
27 | static struct inode *anon_inode_inode; |
28 | static const struct file_operations anon_inode_fops; |
29 | |
30 | static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags, |
31 | const char *dev_name, void *data, |
32 | struct vfsmount *mnt) |
33 | { |
34 | return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC, |
35 | mnt); |
36 | } |
37 | |
38 | static int anon_inodefs_delete_dentry(struct dentry *dentry) |
39 | { |
40 | /* |
41 | * We faked vfs to believe the dentry was hashed when we created it. |
42 | * Now we restore the flag so that dput() will work correctly. |
43 | */ |
44 | dentry->d_flags |= DCACHE_UNHASHED; |
45 | return 1; |
46 | } |
47 | |
48 | static struct file_system_type anon_inode_fs_type = { |
49 | .name = "anon_inodefs", |
50 | .get_sb = anon_inodefs_get_sb, |
51 | .kill_sb = kill_anon_super, |
52 | }; |
53 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
54 | .d_delete = anon_inodefs_delete_dentry, |
55 | }; |
56 | |
57 | /* |
58 | * nop .set_page_dirty method so that people can use .page_mkwrite on |
59 | * anon inodes. |
60 | */ |
61 | static int anon_set_page_dirty(struct page *page) |
62 | { |
63 | return 0; |
64 | }; |
65 | |
66 | static const struct address_space_operations anon_aops = { |
67 | .set_page_dirty = anon_set_page_dirty, |
68 | }; |
69 | |
70 | /** |
71 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
72 | * anonymous inode, and a dentry that describe the "class" |
73 | * of the file |
74 | * |
75 | * @name: [in] name of the "class" of the new file |
76 | * @fops: [in] file operations for the new file |
77 | * @priv: [in] private data for the new file (will be file's private_data) |
78 | * @flags: [in] flags |
79 | * |
80 | * Creates a new file by hooking it on a single inode. This is useful for files |
81 | * that do not need to have a full-fledged inode in order to operate correctly. |
82 | * All the files created with anon_inode_getfile() will share a single inode, |
83 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
84 | * setup. Returns the newly created file* or an error pointer. |
85 | */ |
86 | struct file *anon_inode_getfile(const char *name, |
87 | const struct file_operations *fops, |
88 | void *priv, int flags) |
89 | { |
90 | struct qstr this; |
91 | struct dentry *dentry; |
92 | struct file *file; |
93 | int error; |
94 | |
95 | if (IS_ERR(anon_inode_inode)) |
96 | return ERR_PTR(-ENODEV); |
97 | |
98 | if (fops->owner && !try_module_get(fops->owner)) |
99 | return ERR_PTR(-ENOENT); |
100 | |
101 | /* |
102 | * Link the inode to a directory entry by creating a unique name |
103 | * using the inode sequence number. |
104 | */ |
105 | error = -ENOMEM; |
106 | this.name = name; |
107 | this.len = strlen(name); |
108 | this.hash = 0; |
109 | dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); |
110 | if (!dentry) |
111 | goto err_module; |
112 | |
113 | /* |
114 | * We know the anon_inode inode count is always greater than zero, |
115 | * so we can avoid doing an igrab() and we can use an open-coded |
116 | * atomic_inc(). |
117 | */ |
118 | atomic_inc(&anon_inode_inode->i_count); |
119 | |
120 | dentry->d_op = &anon_inodefs_dentry_operations; |
121 | /* Do not publish this dentry inside the global dentry hash table */ |
122 | dentry->d_flags &= ~DCACHE_UNHASHED; |
123 | d_instantiate(dentry, anon_inode_inode); |
124 | |
125 | error = -ENFILE; |
126 | file = alloc_file(anon_inode_mnt, dentry, |
127 | FMODE_READ | FMODE_WRITE, fops); |
128 | if (!file) |
129 | goto err_dput; |
130 | file->f_mapping = anon_inode_inode->i_mapping; |
131 | |
132 | file->f_pos = 0; |
133 | file->f_flags = O_RDWR | (flags & O_NONBLOCK); |
134 | file->f_version = 0; |
135 | file->private_data = priv; |
136 | |
137 | return file; |
138 | |
139 | err_dput: |
140 | dput(dentry); |
141 | err_module: |
142 | module_put(fops->owner); |
143 | return ERR_PTR(error); |
144 | } |
145 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
146 | |
147 | /** |
148 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
149 | * anonymous inode, and a dentry that describe the "class" |
150 | * of the file |
151 | * |
152 | * @name: [in] name of the "class" of the new file |
153 | * @fops: [in] file operations for the new file |
154 | * @priv: [in] private data for the new file (will be file's private_data) |
155 | * @flags: [in] flags |
156 | * |
157 | * Creates a new file by hooking it on a single inode. This is useful for files |
158 | * that do not need to have a full-fledged inode in order to operate correctly. |
159 | * All the files created with anon_inode_getfd() will share a single inode, |
160 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
161 | * setup. Returns new descriptor or an error code. |
162 | */ |
163 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
164 | void *priv, int flags) |
165 | { |
166 | int error, fd; |
167 | struct file *file; |
168 | |
169 | error = get_unused_fd_flags(flags); |
170 | if (error < 0) |
171 | return error; |
172 | fd = error; |
173 | |
174 | file = anon_inode_getfile(name, fops, priv, flags); |
175 | if (IS_ERR(file)) { |
176 | error = PTR_ERR(file); |
177 | goto err_put_unused_fd; |
178 | } |
179 | fd_install(fd, file); |
180 | |
181 | return fd; |
182 | |
183 | err_put_unused_fd: |
184 | put_unused_fd(fd); |
185 | return error; |
186 | } |
187 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
188 | |
189 | /* |
190 | * A single inode exists for all anon_inode files. Contrary to pipes, |
191 | * anon_inode inodes have no associated per-instance data, so we need |
192 | * only allocate one of them. |
193 | */ |
194 | static struct inode *anon_inode_mkinode(void) |
195 | { |
196 | struct inode *inode = new_inode(anon_inode_mnt->mnt_sb); |
197 | |
198 | if (!inode) |
199 | return ERR_PTR(-ENOMEM); |
200 | |
201 | inode->i_fop = &anon_inode_fops; |
202 | |
203 | inode->i_mapping->a_ops = &anon_aops; |
204 | |
205 | /* |
206 | * Mark the inode dirty from the very beginning, |
207 | * that way it will never be moved to the dirty |
208 | * list because mark_inode_dirty() will think |
209 | * that it already _is_ on the dirty list. |
210 | */ |
211 | inode->i_state = I_DIRTY; |
212 | inode->i_mode = S_IRUSR | S_IWUSR; |
213 | inode->i_uid = current_fsuid(); |
214 | inode->i_gid = current_fsgid(); |
215 | inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; |
216 | return inode; |
217 | } |
218 | |
219 | static int __init anon_inode_init(void) |
220 | { |
221 | int error; |
222 | |
223 | error = register_filesystem(&anon_inode_fs_type); |
224 | if (error) |
225 | goto err_exit; |
226 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
227 | if (IS_ERR(anon_inode_mnt)) { |
228 | error = PTR_ERR(anon_inode_mnt); |
229 | goto err_unregister_filesystem; |
230 | } |
231 | anon_inode_inode = anon_inode_mkinode(); |
232 | if (IS_ERR(anon_inode_inode)) { |
233 | error = PTR_ERR(anon_inode_inode); |
234 | goto err_mntput; |
235 | } |
236 | |
237 | return 0; |
238 | |
239 | err_mntput: |
240 | mntput(anon_inode_mnt); |
241 | err_unregister_filesystem: |
242 | unregister_filesystem(&anon_inode_fs_type); |
243 | err_exit: |
244 | panic(KERN_ERR "anon_inode_init() failed (%d)\n", error); |
245 | } |
246 | |
247 | fs_initcall(anon_inode_init); |
248 | |
249 |
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