[RFC][PATCH 0/4] Enhanced file stat system call [ver #2]

From: David Howells
Date: Fri Nov 18 2016 - 11:20:38 EST

Implement a new system call to provide enhanced file stats. The patches can
be found here:



The first patch provides this new system call:

long ret = statx(int dfd,
const char *filename,
unsigned atflag,
unsigned mask,
struct statx *buffer);

This is an enhanced file stat function that provides a number of useful
features, in summary:

(1) More information: creation time, data version number and attributes.
A subset of these is available through a number of filesystems (such
as CIFS, NFS, AFS, Ext4 and BTRFS).

(2) Lightweight stat (AT_STATX_DONT_SYNC): Ask for just those details of
interest, and allow a network fs to approximate anything not of
interest, without going to the server.

(3) Heavyweight stat (AT_STATX_FORCE_SYNC): Force a network fs to flush
buffers and go to the server, even if it thinks its cached attributes
are up to date.

(4) Allow the filesystem to indicate what it can/cannot provide: A
filesystem can now say it doesn't support a standard stat feature if
that isn't available.

(5) Make the fields a consistent size on all arches, and make them large.

(6) Can be extended by using more request flags and using up the padding
space in the statx struct.

(7) Takes dfd, filename and flags in a similar way to fstatat().

Note that no lstat() equivalent is required as that can be implemented
through statx() with atflag == 0. There is also no fstat() equivalent as
that can be implemented through statx() with filename == NULL and the
relevant fd passed as dfd.


A test program is added into samples/statx/ by the first patch.


Ver #2:

- Turn the AT_STATX_*_SYNC flags into a 2-bit field with three options and
give EINVAL if the undefined option in that field is specified.

- Removed various STATX_ATTR_* flags for lack of definition - can be
reinstated later.

- Removed stx_version and STATX_VERSION for lack of a way to make it
consistent - can be reinstated later.

David Howells (4):
statx: Add a system call to make enhanced file info available
statx: Ext4: Return enhanced file attributes
statx: NFS: Return enhanced file attributes
statx: AFS: Return enhanced file attributes

arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
fs/afs/inode.c | 11 +
fs/exportfs/expfs.c | 4
fs/ext4/ext4.h | 2
fs/ext4/file.c | 2
fs/ext4/inode.c | 36 ++++
fs/ext4/namei.c | 2
fs/ext4/symlink.c | 2
fs/nfs/inode.c | 32 +++
fs/stat.c | 296 +++++++++++++++++++++++++++++---
include/linux/fs.h | 5 -
include/linux/stat.h | 19 +-
include/linux/syscalls.h | 3
include/uapi/linux/fcntl.h | 5 +
include/uapi/linux/stat.h | 116 +++++++++++++
samples/Kconfig | 5 +
samples/Makefile | 3
samples/statx/Makefile | 10 +
samples/statx/test-statx.c | 248 +++++++++++++++++++++++++++
20 files changed, 746 insertions(+), 57 deletions(-)
create mode 100644 samples/statx/Makefile
create mode 100644 samples/statx/test-statx.c