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