Commit 5dc8bf81 authored by Davide Libenzi's avatar Davide Libenzi Committed by Linus Torvalds

signal/timer/event fds: anonymous inode source

This patch add an anonymous inode source, to be used for files that need
and inode only in order to create a file*. We do not care of having an
inode for each file, and we do not even care of having different names in
the associated dentries (dentry names will be same for classes of file*).
This allow code reuse, and will be used by epoll, signalfd and timerfd
(and whatever else there'll be).
Signed-off-by: default avatarDavide Libenzi <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 325aa33d
......@@ -22,6 +22,7 @@ endif
obj-$(CONFIG_INOTIFY) += inotify.o
obj-$(CONFIG_INOTIFY_USER) += inotify_user.o
obj-$(CONFIG_EPOLL) += eventpoll.o
obj-$(CONFIG_ANON_INODES) += anon_inodes.o
obj-$(CONFIG_COMPAT) += compat.o compat_ioctl.o
nfsd-$(CONFIG_NFSD) := nfsctl.o
* fs/anon_inodes.c
* Copyright (C) 2007 Davide Libenzi <>
* Thanks to Arnd Bergmann for code review and suggestions.
* More changes for Thomas Gleixner suggestions.
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/magic.h>
#include <linux/anon_inodes.h>
#include <asm/uaccess.h>
static struct vfsmount *anon_inode_mnt __read_mostly;
static struct inode *anon_inode_inode;
static const struct file_operations anon_inode_fops;
static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data,
struct vfsmount *mnt)
return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
static int anon_inodefs_delete_dentry(struct dentry *dentry)
* We faked vfs to believe the dentry was hashed when we created it.
* Now we restore the flag so that dput() will work correctly.
dentry->d_flags |= DCACHE_UNHASHED;
return 1;
static struct file_system_type anon_inode_fs_type = {
.name = "anon_inodefs",
.get_sb = anon_inodefs_get_sb,
.kill_sb = kill_anon_super,
static struct dentry_operations anon_inodefs_dentry_operations = {
.d_delete = anon_inodefs_delete_dentry,
* anon_inode_getfd - creates a new file instance by hooking it up to and
* anonymous inode, and a dentry that describe the "class"
* of the file
* @pfd: [out] pointer to the file descriptor
* @dpinode: [out] pointer to the inode
* @pfile: [out] pointer to the file struct
* @name: [in] name of the "class" of the new file
* @fops [in] file operations for the new file
* @priv [in] private data for the new file (will be file's private_data)
* Creates a new file by hooking it on a single inode. This is useful for files
* that do not need to have a full-fledged inode in order to operate correctly.
* All the files created with anon_inode_getfd() will share a single inode, by
* hence saving memory and avoiding code duplication for the file/inode/dentry
* setup.
int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
const char *name, const struct file_operations *fops,
void *priv)
struct qstr this;
struct dentry *dentry;
struct inode *inode;
struct file *file;
int error, fd;
if (IS_ERR(anon_inode_inode))
return -ENODEV;
file = get_empty_filp();
if (!file)
return -ENFILE;
inode = igrab(anon_inode_inode);
if (IS_ERR(inode)) {
error = PTR_ERR(inode);
goto err_put_filp;
error = get_unused_fd();
if (error < 0)
goto err_iput;
fd = error;
* Link the inode to a directory entry by creating a unique name
* using the inode sequence number.
error = -ENOMEM; = name;
this.len = strlen(name);
this.hash = 0;
dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
if (!dentry)
goto err_put_unused_fd;
dentry->d_op = &anon_inodefs_dentry_operations;
/* Do not publish this dentry inside the global dentry hash table */
dentry->d_flags &= ~DCACHE_UNHASHED;
d_instantiate(dentry, inode);
file->f_path.mnt = mntget(anon_inode_mnt);
file->f_path.dentry = dentry;
file->f_mapping = inode->i_mapping;
file->f_pos = 0;
file->f_flags = O_RDWR;
file->f_op = fops;
file->f_mode = FMODE_READ | FMODE_WRITE;
file->f_version = 0;
file->private_data = priv;
fd_install(fd, file);
*pfd = fd;
*pinode = inode;
*pfile = file;
return 0;
return error;
* A single inode exist for all anon_inode files. Contrary to pipes,
* anon_inode inodes has no per-instance data associated, so we can avoid
* the allocation of multiple of them.
static struct inode *anon_inode_mkinode(void)
struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
if (!inode)
return ERR_PTR(-ENOMEM);
inode->i_fop = &anon_inode_fops;
* Mark the inode dirty from the very beginning,
* that way it will never be moved to the dirty
* list because mark_inode_dirty() will think
* that it already _is_ on the dirty list.
inode->i_state = I_DIRTY;
inode->i_mode = S_IRUSR | S_IWUSR;
inode->i_uid = current->fsuid;
inode->i_gid = current->fsgid;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
return inode;
static int __init anon_inode_init(void)
int error;
error = register_filesystem(&anon_inode_fs_type);
if (error)
goto err_exit;
anon_inode_mnt = kern_mount(&anon_inode_fs_type);
if (IS_ERR(anon_inode_mnt)) {
error = PTR_ERR(anon_inode_mnt);
goto err_unregister_filesystem;
anon_inode_inode = anon_inode_mkinode();
if (IS_ERR(anon_inode_inode)) {
error = PTR_ERR(anon_inode_inode);
goto err_mntput;
return 0;
panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
* include/linux/anon_inodes.h
* Copyright (C) 2007 Davide Libenzi <>
int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
const char *name, const struct file_operations *fops,
void *priv);
#endif /* _LINUX_ANON_INODES_H */
......@@ -14,6 +14,7 @@
#define ISOFS_SUPER_MAGIC 0x9660
#define JFFS2_SUPER_MAGIC 0x72b6
#define KVMFS_SUPER_MAGIC 0x19700426
#define ANON_INODE_FS_MAGIC 0x09041934
#define MINIX_SUPER_MAGIC 0x137F /* original minix fs */
#define MINIX_SUPER_MAGIC2 0x138F /* minix fs, 30 char names */
......@@ -475,9 +475,19 @@ config FUTEX
support for "fast userspace mutexes". The resulting kernel may not
run glibc-based applications correctly.
bool "Enable anonymous inode source" if EMBEDDED
default y
Anonymous inode source for pseudo-files like epoll, signalfd,
timerfd and eventfd.
If unsure, say Y.
config EPOLL
bool "Enable eventpoll support" if EMBEDDED
default y
depends on ANON_INODES
Disabling this option will cause the kernel to be built without
support for epoll family of system calls.
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