linux-kernel - Re: pread2/ pwrite2

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Message-ID: <CAH2r5mtwQEJ1q=a_4TSQyY=Qt7TZ7Dtj9oVGfCHJ+Enrj8v5qQ@mail.gmail.com>
Date:	Fri, 9 Jan 2015 13:30:31 -0600
From:	Steve French <smfrench@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Milosz Tanski <milosz@...in.com>
Subject: Re: pread2/ pwrite2

On Thu, Jan 8, 2015 at 5:49 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Tue, Jan 06, 2015 at 12:47:14AM -0800, Andrew Morton wrote:
>> > progress, which is a bit frustrating.
>>
>> I took a look at pread2() as well and I have two main issues:
>>
>> - The patchset includes a pwrite2() syscall which has nothing to do
>>   with nonblocking reads and which was poorly described and had little
>>   justification for inclusion.
>
> It allows to do O_SYNC writes on a per-I/O basis.  This is very useful
> for file servers (smb, cifs) as well as storage target devices.

This would be particularly useful for SMB3 as the protocol now allows
write-through vs. no-write-through flag on every write request (not just
on an open, it can be changed on a particular i/o to write-through).
There is also a cache/no-cache hint that can be sent on reads/writes in
the newest SMB3 dialect well (but it is less clear to me how we would
ever decide to set that on the Linux client).




-- 
Thanks,

Steve
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