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 */
anon_inodefs_dname(struct dentry * dentry,char * buffer,int buflen)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 */
anon_set_page_dirty(struct page * page)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 */
anon_inode_mkinode(struct super_block * s)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
anon_inodefs_mount(struct file_system_type * fs_type,int flags,const char * dev_name,void * data)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 */
anon_inode_getfile(const char * name,const struct file_operations * fops,void * priv,int flags)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 int error;
135
136 if (IS_ERR(anon_inode_inode))
137 return ERR_PTR(-ENODEV);
138
139 if (fops->owner && !try_module_get(fops->owner))
140 return ERR_PTR(-ENOENT);
141
142 /*
143 * Link the inode to a directory entry by creating a unique name
144 * using the inode sequence number.
145 */
146 error = -ENOMEM;
147 this.name = name;
148 this.len = strlen(name);
149 this.hash = 0;
150 path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
151 if (!path.dentry)
152 goto err_module;
153
154 path.mnt = mntget(anon_inode_mnt);
155 /*
156 * We know the anon_inode inode count is always greater than zero,
157 * so ihold() is safe.
158 */
159 ihold(anon_inode_inode);
160
161 d_instantiate(path.dentry, anon_inode_inode);
162
163 error = -ENFILE;
164 file = alloc_file(&path, OPEN_FMODE(flags), fops);
165 if (!file)
166 goto err_dput;
167 file->f_mapping = anon_inode_inode->i_mapping;
168
169 file->f_pos = 0;
170 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
171 file->f_version = 0;
172 file->private_data = priv;
173
174 return file;
175
176 err_dput:
177 path_put(&path);
178 err_module:
179 module_put(fops->owner);
180 return ERR_PTR(error);
181 }
182 EXPORT_SYMBOL_GPL(anon_inode_getfile);
183
184 /**
185 * anon_inode_getfd - creates a new file instance by hooking it up to an
186 * anonymous inode, and a dentry that describe the "class"
187 * of the file
188 *
189 * @name: [in] name of the "class" of the new file
190 * @fops: [in] file operations for the new file
191 * @priv: [in] private data for the new file (will be file's private_data)
192 * @flags: [in] flags
193 *
194 * Creates a new file by hooking it on a single inode. This is useful for files
195 * that do not need to have a full-fledged inode in order to operate correctly.
196 * All the files created with anon_inode_getfd() will share a single inode,
197 * hence saving memory and avoiding code duplication for the file/inode/dentry
198 * setup. Returns new descriptor or an error code.
199 */
anon_inode_getfd(const char * name,const struct file_operations * fops,void * priv,int flags)200 int anon_inode_getfd(const char *name, const struct file_operations *fops,
201 void *priv, int flags)
202 {
203 int error, fd;
204 struct file *file;
205
206 error = get_unused_fd_flags(flags);
207 if (error < 0)
208 return error;
209 fd = error;
210
211 file = anon_inode_getfile(name, fops, priv, flags);
212 if (IS_ERR(file)) {
213 error = PTR_ERR(file);
214 goto err_put_unused_fd;
215 }
216 fd_install(fd, file);
217
218 return fd;
219
220 err_put_unused_fd:
221 put_unused_fd(fd);
222 return error;
223 }
224 EXPORT_SYMBOL_GPL(anon_inode_getfd);
225
anon_inode_init(void)226 static int __init anon_inode_init(void)
227 {
228 int error;
229
230 error = register_filesystem(&anon_inode_fs_type);
231 if (error)
232 goto err_exit;
233 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
234 if (IS_ERR(anon_inode_mnt)) {
235 error = PTR_ERR(anon_inode_mnt);
236 goto err_unregister_filesystem;
237 }
238 return 0;
239
240 err_unregister_filesystem:
241 unregister_filesystem(&anon_inode_fs_type);
242 err_exit:
243 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
244 }
245
246 fs_initcall(anon_inode_init);
247
248