Commit 990d6c2d authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Al Viro

vfs: Add name to file handle conversion support

The syscall also return mount id which can be used
to lookup file system specific information such as uuid
in /proc/<pid>/mountinfo
Signed-off-by: default avatarAneesh Kumar K.V <>
Signed-off-by: default avatarAl Viro <>
parent f52e0c11
......@@ -47,7 +47,7 @@ config FS_POSIX_ACL
def_bool n
bool "Enable POSIX file locking API" if EXPERT
......@@ -48,6 +48,8 @@ obj-$(CONFIG_FS_POSIX_ACL) += posix_acl.o xattr_acl.o
obj-$(CONFIG_NFS_COMMON) += nfs_common/
obj-$(CONFIG_GENERIC_ACL) += generic_acl.o
obj-$(CONFIG_FHANDLE) += fhandle.o
obj-y += quota/
obj-$(CONFIG_PROC_FS) += proc/
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/exportfs.h>
#include <asm/uaccess.h>
#include "internal.h"
static long do_sys_name_to_handle(struct path *path,
struct file_handle __user *ufh,
int __user *mnt_id)
long retval;
struct file_handle f_handle;
int handle_dwords, handle_bytes;
struct file_handle *handle = NULL;
* We need t make sure wether the file system
* support decoding of the file handle
if (!path->mnt->mnt_sb->s_export_op ||
if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
return -EFAULT;
if (f_handle.handle_bytes > MAX_HANDLE_SZ)
return -EINVAL;
handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
if (!handle)
return -ENOMEM;
/* convert handle size to multiple of sizeof(u32) */
handle_dwords = f_handle.handle_bytes >> 2;
/* we ask for a non connected handle */
retval = exportfs_encode_fh(path->dentry,
(struct fid *)handle->f_handle,
&handle_dwords, 0);
handle->handle_type = retval;
/* convert handle size to bytes */
handle_bytes = handle_dwords * sizeof(u32);
handle->handle_bytes = handle_bytes;
if ((handle->handle_bytes > f_handle.handle_bytes) ||
(retval == 255) || (retval == -ENOSPC)) {
/* As per old exportfs_encode_fh documentation
* we could return ENOSPC to indicate overflow
* But file system returned 255 always. So handle
* both the values
* set the handle size to zero so we copy only
* non variable part of the file_handle
handle_bytes = 0;
retval = -EOVERFLOW;
} else
retval = 0;
/* copy the mount id */
if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
copy_to_user(ufh, handle,
sizeof(struct file_handle) + handle_bytes))
retval = -EFAULT;
return retval;
* sys_name_to_handle_at: convert name to handle
* @dfd: directory relative to which name is interpreted if not absolute
* @name: name that should be converted to handle.
* @handle: resulting file handle
* @mnt_id: mount id of the file system containing the file
* @flag: flag value to indicate whether to follow symlink or not
* @handle->handle_size indicate the space available to store the
* variable part of the file handle in bytes. If there is not
* enough space, the field is updated to return the minimum
* value required.
SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
struct file_handle __user *, handle, int __user *, mnt_id,
int, flag)
struct path path;
int lookup_flags;
int err;
if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
return -EINVAL;
lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
if (flag & AT_EMPTY_PATH)
lookup_flags |= LOOKUP_EMPTY;
err = user_path_at(dfd, name, lookup_flags, &path);
if (!err) {
err = do_sys_name_to_handle(&path, handle, mnt_id);
return err;
......@@ -8,6 +8,9 @@ struct inode;
struct super_block;
struct vfsmount;
/* limit the handle size to NFSv4 handle size now */
#define MAX_HANDLE_SZ 128
* The fileid_type identifies how the file within the filesystem is encoded.
* In theory this is freely set and parsed by the filesystem, but we try to
......@@ -978,6 +978,13 @@ struct file {
struct file_handle {
__u32 handle_bytes;
int handle_type;
/* file identifier */
unsigned char f_handle[0];
#define get_file(x) atomic_long_inc(&(x)->f_count)
#define fput_atomic(x) atomic_long_add_unless(&(x)->f_count, -1, 1)
#define file_count(x) atomic_long_read(&(x)->f_count)
......@@ -62,6 +62,7 @@ struct robust_list_head;
struct getcpu_cache;
struct old_linux_dirent;
struct perf_event_attr;
struct file_handle;
#include <linux/types.h>
#include <linux/aio_abi.h>
......@@ -832,5 +833,7 @@ asmlinkage long sys_mmap_pgoff(unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags,
unsigned long fd, unsigned long pgoff);
asmlinkage long sys_old_mmap(struct mmap_arg_struct __user *arg);
asmlinkage long sys_name_to_handle_at(int dfd, const char __user *name,
struct file_handle __user *handle,
int __user *mnt_id, int flag);
......@@ -287,6 +287,18 @@ config BSD_PROCESS_ACCT_V3
for processing it. A preliminary version of these tools is available
at <>.
config FHANDLE
bool "open by fhandle syscalls"
If you say Y here, a user level program will be able to map
file names to handle and then later use the handle for
different file system operations. This is useful in implementing
userspace file servers, which now track files using handles instead
of names. The handle would remain the same even if file names
get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
bool "Export task/process statistics through netlink (EXPERIMENTAL)"
depends on NET
......@@ -186,3 +186,6 @@ cond_syscall(sys_perf_event_open);
/* fanotify! */
/* open by handle */
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