4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 * Thanks to Arnd Bergmann for code review and suggestions.
7 * More changes for Thomas Gleixner suggestions.
11 #include <linux/file.h>
12 #include <linux/poll.h>
13 #include <linux/slab.h>
14 #include <linux/init.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>
22 #include <asm/uaccess.h>
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;
28 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
29 const char *dev_name, void *data,
32 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
36 static int anon_inodefs_delete_dentry(struct dentry *dentry)
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.
42 dentry->d_flags |= DCACHE_UNHASHED;
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,
51 static struct dentry_operations anon_inodefs_dentry_operations = {
52 .d_delete = anon_inodefs_delete_dentry,
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"
60 * @pfd: [out] pointer to the file descriptor
61 * @dpinode: [out] pointer to the inode
62 * @pfile: [out] pointer to the file struct
63 * @name: [in] name of the "class" of the new file
64 * @fops [in] file operations for the new file
65 * @priv [in] private data for the new file (will be file's private_data)
67 * Creates a new file by hooking it on a single inode. This is useful for files
68 * that do not need to have a full-fledged inode in order to operate correctly.
69 * All the files created with anon_inode_getfd() will share a single inode,
70 * hence saving memory and avoiding code duplication for the file/inode/dentry
73 int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
74 const char *name, const struct file_operations *fops,
78 struct dentry *dentry;
82 if (IS_ERR(anon_inode_inode))
84 file = get_empty_filp();
88 error = get_unused_fd();
94 * Link the inode to a directory entry by creating a unique name
95 * using the inode sequence number.
99 this.len = strlen(name);
101 dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
103 goto err_put_unused_fd;
106 * We know the anon_inode inode count is always greater than zero,
107 * so we can avoid doing an igrab() and we can use an open-coded
110 atomic_inc(&anon_inode_inode->i_count);
112 dentry->d_op = &anon_inodefs_dentry_operations;
113 /* Do not publish this dentry inside the global dentry hash table */
114 dentry->d_flags &= ~DCACHE_UNHASHED;
115 d_instantiate(dentry, anon_inode_inode);
117 file->f_path.mnt = mntget(anon_inode_mnt);
118 file->f_path.dentry = dentry;
119 file->f_mapping = anon_inode_inode->i_mapping;
122 file->f_flags = O_RDWR;
124 file->f_mode = FMODE_READ | FMODE_WRITE;
126 file->private_data = priv;
128 fd_install(fd, file);
131 *pinode = anon_inode_inode;
141 EXPORT_SYMBOL_GPL(anon_inode_getfd);
144 * A single inode exists for all anon_inode files. Contrary to pipes,
145 * anon_inode inodes have no associated per-instance data, so we need
146 * only allocate one of them.
148 static struct inode *anon_inode_mkinode(void)
150 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
153 return ERR_PTR(-ENOMEM);
155 inode->i_fop = &anon_inode_fops;
158 * Mark the inode dirty from the very beginning,
159 * that way it will never be moved to the dirty
160 * list because mark_inode_dirty() will think
161 * that it already _is_ on the dirty list.
163 inode->i_state = I_DIRTY;
164 inode->i_mode = S_IRUSR | S_IWUSR;
165 inode->i_uid = current->fsuid;
166 inode->i_gid = current->fsgid;
167 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
171 static int __init anon_inode_init(void)
175 error = register_filesystem(&anon_inode_fs_type);
178 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
179 if (IS_ERR(anon_inode_mnt)) {
180 error = PTR_ERR(anon_inode_mnt);
181 goto err_unregister_filesystem;
183 anon_inode_inode = anon_inode_mkinode();
184 if (IS_ERR(anon_inode_inode)) {
185 error = PTR_ERR(anon_inode_inode);
192 mntput(anon_inode_mnt);
193 err_unregister_filesystem:
194 unregister_filesystem(&anon_inode_fs_type);
196 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
199 fs_initcall(anon_inode_init);