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Message-ID: <564F4F4E.8060603@schaufler-ca.com>
Date: Fri, 20 Nov 2015 08:50:22 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: David Howells <dhowells@...hat.com>, arnd@...db.de
Cc: 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 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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