Re: [RFC][PATCH 00/12] Enhanced file stat system call
From: Casey Schaufler
Date: Fri Nov 20 2015 - 11:57:06 EST
On 11/20/2015 6:54 AM, David Howells wrote:
Implement new system calls to provide enhanced file stats and enhanced
filesystem stats. The patches can be found here:
http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=xstat
===========
DESCRIPTION
===========
The third 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,
flags/attributes. A subset of these is available through a number of
filesystems (such as CIFS, NFS, AFS, Ext4 and BTRFS).
(2) Lightweight stat (AT_NO_ATTR_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_FORCE_ATTR_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.
How about relevant xattrs? SELinux context, ACL, that sort of thing.
The fact that these are optional should be taken care of by (4).
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.
The seventh patch provides another new system call:
long ret = fsinfo(int dfd,
const char *filename,
unsigned atflag,
unsigned request,
void *buffer);
This is an enhanced filesystem stat and information retrieval function that
provides more information, in summary:
(1) All the information provided by statfs() and more. The fields are
made large.
(2) Provides information about timestamp range and resolution to
complement statx().
(3) Provides information about IOC flags supported in statx()'s return.
(4) Provides volume binary IDs and UUIDs.
(5) Provides the filesystem name according to the kernel as a string
(eg. "ext4" or "nfs3") in addition to the magic number.
(6) Provides information obtained from network filesystems, such as volume
and domain names.
(7) Has lots of spare space that can be used for future extenstions and a
bit mask indicating what was provided.
Note that I've added a 'request' identifier. This is to select the set of
data to be returned. The idea is that 'buffer' points to a fixed-size
struct selected by request. Currently only 0 is available and this refers
to 'struct fsinfo'. However, I could split up the buffer into say 3:
(0) statfs-type information
(1) Timestamp and IOC flags info.
(2) Network fs strings.
However, some of this might be better retrieved through getxattr().
=======
TESTING
=======
Test programs are added into samples/statx/ by the appropriate patches.
David
---
David Howells (12):
Ext4: Fix extended timestamp encoding and decoding
statx: Provide IOC flags for Windows fs attributes
statx: Add a system call to make enhanced file info available
statx: AFS: Return enhanced file attributes
statx: Ext4: Return enhanced file attributes
statx: NFS: Return enhanced file attributes
statx: CIFS: Return enhanced attributes
fsinfo: Add a system call to make enhanced filesystem info available
fsinfo: Ext4: Return information through the filesystem info syscall
fsinfo: AFS: Return information through the filesystem info syscall
fsinfo: NFS: Return information through the filesystem info syscall
fsinfo: CIFS: Return information through the filesystem info syscall
arch/x86/entry/syscalls/syscall_32.tbl | 2
arch/x86/entry/syscalls/syscall_64.tbl | 2
fs/afs/inode.c | 23 ++
fs/afs/super.c | 39 ++++
fs/cifs/cifsfs.c | 25 +++
fs/cifs/cifsfs.h | 4
fs/cifs/cifsglob.h | 8 +
fs/cifs/dir.c | 2
fs/cifs/inode.c | 124 ++++++++++---
fs/cifs/netmisc.c | 4
fs/exportfs/expfs.c | 4
fs/ext4/ext4.h | 24 ++-
fs/ext4/file.c | 2
fs/ext4/inode.c | 31 +++
fs/ext4/namei.c | 2
fs/ext4/super.c | 39 ++++
fs/ext4/symlink.c | 2
fs/nfs/inode.c | 45 ++++-
fs/nfs/internal.h | 1
fs/nfs/nfs4super.c | 1
fs/nfs/super.c | 58 ++++++
fs/ntfs/time.h | 2
fs/stat.c | 305 +++++++++++++++++++++++++++++---
fs/statfs.c | 218 +++++++++++++++++++++++
include/linux/fs.h | 7 +
include/linux/stat.h | 14 +
include/linux/syscalls.h | 6 +
include/linux/time64.h | 2
include/uapi/linux/fcntl.h | 2
include/uapi/linux/fs.h | 7 +
include/uapi/linux/stat.h | 185 +++++++++++++++++++
samples/Makefile | 3
samples/statx/Makefile | 13 +
samples/statx/test-fsinfo.c | 179 +++++++++++++++++++
samples/statx/test-statx.c | 273 +++++++++++++++++++++++++++++
35 files changed, 1558 insertions(+), 100 deletions(-)
create mode 100644 samples/statx/Makefile
create mode 100644 samples/statx/test-fsinfo.c
create mode 100644 samples/statx/test-statx.c
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