linux-ext4 - Re: [PATCH 3/3] Add a pair of system calls to make extended file stats available

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Message-ID: <AANLkTimieV9ybz2XrD29tvz1mogdMA5VHH4lNSwPovoE@mail.gmail.com>
Date:	Tue, 29 Jun 2010 17:33:56 -0500
From:	Steve French <smfrench@...il.com>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	David Howells <dhowells@...hat.com>, viro@...iv.linux.org.uk,
	jlayton@...hat.com, mcao@...ibm.com,
	aneesh.kumar@...ux.vnet.ibm.com, linux-cifs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	samba-technical@...ts.samba.org, sjayaraman@...e.de,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/3] Add a pair of system calls to make extended file 
	stats available

On Tue, Jun 29, 2010 at 5:13 PM, Ulrich Drepper <drepper@...il.com> wrote:
> On Tue, Jun 29, 2010 at 13:03, David Howells <dhowells@...hat.com> wrote:
>> Add a pair of system calls to make extended file stats available, including
>> file creation time, inode version and data version where available through the
>> underlying filesystem:
>
> If you add something like this you might want to integrate another
> extension.  This has been discussed a long time ago.  In almost no
> situation all the information is needed.  Some of the pieces of
> information returned by the syscall might be harder to collect than
> other.  It makes sense in such a situation to allow the caller to
> specify what she is interested in.  A bitmask of some sort.  This was
> brought up by the HPC people with gigantic filesystems.
>
> For this the syscall interface should have a parameter to specify what
> is requested and the stat-like structure should have a field
> specifying what is actually present.  The latter bitmask must be a
> superset of the former.
>
> Previous discussions centered around reusing the stat data structure
> and somehow make it work.  But no clean solution was found.  If a new
> structure is added anyway this could solve the issue.

That makes sense, especially for network file systems.  NFSv4
protocol spec anticipates that:

"With the NFS version 4 protocol, the client is able query what attributes
   the server supports and construct requests with only those supported
   attributes (or a subset thereof)."

and we were talking about something similar for SMB2 Unix Extensions
(posix extensions) at the last plugfest (for SMB2 kernel
client to Samba)
and testing events.
-- 
Thanks,

Steve
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