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/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>
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>
24 #include <asm/uaccess.h>
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;
30 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
31 const char *dev_name, void *data,
34 return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
38 static int anon_inodefs_delete_dentry(struct dentry *dentry)
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.
44 dentry->d_flags |= DCACHE_UNHASHED;
49 * anon_inodefs_dname() is called from d_path().
51 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
53 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
57 static struct file_system_type anon_inode_fs_type = {
58 .name = "anon_inodefs",
59 .get_sb = anon_inodefs_get_sb,
60 .kill_sb = kill_anon_super,
62 static const struct dentry_operations anon_inodefs_dentry_operations = {
63 .d_delete = anon_inodefs_delete_dentry,
64 .d_dname = anon_inodefs_dname,
68 * nop .set_page_dirty method so that people can use .page_mkwrite on
71 static int anon_set_page_dirty(struct page *page)
76 static const struct address_space_operations anon_aops = {
77 .set_page_dirty = anon_set_page_dirty,
81 * anon_inode_getfd - creates a new file instance by hooking it up to an
82 * anonymous inode, and a dentry that describe the "class"
85 * @name: [in] name of the "class" of the new file
86 * @fops: [in] file operations for the new file
87 * @priv: [in] private data for the new file (will be file's private_data)
90 * Creates a new file by hooking it on a single inode. This is useful for files
91 * that do not need to have a full-fledged inode in order to operate correctly.
92 * All the files created with anon_inode_getfile() will share a single inode,
93 * hence saving memory and avoiding code duplication for the file/inode/dentry
94 * setup. Returns the newly created file* or an error pointer.
96 struct file *anon_inode_getfile(const char *name,
97 const struct file_operations *fops,
98 void *priv, int flags)
105 if (IS_ERR(anon_inode_inode))
106 return ERR_PTR(-ENODEV);
108 if (fops->owner && !try_module_get(fops->owner))
109 return ERR_PTR(-ENOENT);
112 * Link the inode to a directory entry by creating a unique name
113 * using the inode sequence number.
117 this.len = strlen(name);
119 path.dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
123 path.mnt = mntget(anon_inode_mnt);
125 * We know the anon_inode inode count is always greater than zero,
126 * so we can avoid doing an igrab() and we can use an open-coded
129 atomic_inc(&anon_inode_inode->i_count);
131 path.dentry->d_op = &anon_inodefs_dentry_operations;
132 /* Do not publish this dentry inside the global dentry hash table */
133 path.dentry->d_flags &= ~DCACHE_UNHASHED;
134 d_instantiate(path.dentry, anon_inode_inode);
137 file = alloc_file(&path, FMODE_READ | FMODE_WRITE, fops);
140 file->f_mapping = anon_inode_inode->i_mapping;
143 file->f_flags = O_RDWR | (flags & O_NONBLOCK);
145 file->private_data = priv;
152 module_put(fops->owner);
153 return ERR_PTR(error);
155 EXPORT_SYMBOL_GPL(anon_inode_getfile);
158 * anon_inode_getfd - creates a new file instance by hooking it up to an
159 * anonymous inode, and a dentry that describe the "class"
162 * @name: [in] name of the "class" of the new file
163 * @fops: [in] file operations for the new file
164 * @priv: [in] private data for the new file (will be file's private_data)
167 * Creates a new file by hooking it on a single inode. This is useful for files
168 * that do not need to have a full-fledged inode in order to operate correctly.
169 * All the files created with anon_inode_getfd() will share a single inode,
170 * hence saving memory and avoiding code duplication for the file/inode/dentry
171 * setup. Returns new descriptor or an error code.
173 int anon_inode_getfd(const char *name, const struct file_operations *fops,
174 void *priv, int flags)
179 error = get_unused_fd_flags(flags);
184 file = anon_inode_getfile(name, fops, priv, flags);
186 error = PTR_ERR(file);
187 goto err_put_unused_fd;
189 fd_install(fd, file);
197 EXPORT_SYMBOL_GPL(anon_inode_getfd);
200 * A single inode exists for all anon_inode files. Contrary to pipes,
201 * anon_inode inodes have no associated per-instance data, so we need
202 * only allocate one of them.
204 static struct inode *anon_inode_mkinode(void)
206 struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
209 return ERR_PTR(-ENOMEM);
211 inode->i_fop = &anon_inode_fops;
213 inode->i_mapping->a_ops = &anon_aops;
216 * Mark the inode dirty from the very beginning,
217 * that way it will never be moved to the dirty
218 * list because mark_inode_dirty() will think
219 * that it already _is_ on the dirty list.
221 inode->i_state = I_DIRTY;
222 inode->i_mode = S_IRUSR | S_IWUSR;
223 inode->i_uid = current_fsuid();
224 inode->i_gid = current_fsgid();
225 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
229 static int __init anon_inode_init(void)
233 error = register_filesystem(&anon_inode_fs_type);
236 anon_inode_mnt = kern_mount(&anon_inode_fs_type);
237 if (IS_ERR(anon_inode_mnt)) {
238 error = PTR_ERR(anon_inode_mnt);
239 goto err_unregister_filesystem;
241 anon_inode_inode = anon_inode_mkinode();
242 if (IS_ERR(anon_inode_inode)) {
243 error = PTR_ERR(anon_inode_inode);
250 mntput(anon_inode_mnt);
251 err_unregister_filesystem:
252 unregister_filesystem(&anon_inode_fs_type);
254 panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
257 fs_initcall(anon_inode_init);