signal/timer/event fds: anonymous inode source

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 <davidel@xmailserver.org>

 *

 *  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,

			     mnt);

}

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;

	this.name = 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;

err_put_unused_fd:

	put_unused_fd(fd);

err_iput:

	iput(inode);

err_put_filp:

	put_filp(file);

	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;

err_mntput:

	mntput(anon_inode_mnt);

err_unregister_filesystem:

	unregister_filesystem(&anon_inode_fs_type);

err_exit:

	panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);

}

fs_initcall(anon_inode_init);

/*

 *  include/linux/anon_inodes.h

 *

 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>

 *

 */

#ifndef _LINUX_ANON_INODES_H

#define _LINUX_ANON_INODES_H

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 */

#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 */

	  support for "fast userspace mutexes".  The resulting kernel may not

	  run glibc-based applications correctly.

config ANON_INODES

	bool "Enable anonymous inode source" if EMBEDDED

	default y

	help

	  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

	help

	  Disabling this option will cause the kernel to be built without

	  support for epoll family of system calls.