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Date: Tue, 24 Nov 2015 09:28:26 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: David Howells <dhowells@...hat.com>, arnd@...db.de,
linux-afs@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-ext4@...r.kernel.org
Subject: Re: [RFC][PATCH 00/12] Enhanced file stat system call
On Nov 20, 2015, at 9:50 AM, Casey Schaufler <casey@...aufler-ca.com> wrote:
> 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).
Given that there are a wide variety of xattrs that different apps might be
interested in, this would probably be better served by an enhancement to
getxattr() or listxattr() to be able to retrieve a whole list of xattrs
at once, possibly with some wildcard support (e.g. "security.*") instead
of returning all or a specific subset of xattrs with statx() (which is
geared toward fixed-size attributes).
Cheers, Andreas
>> 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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>
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Cheers, Andreas
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