Re: pread2/ pwrite2

[Steve French]

On Thu, Jan 8, 2015 at 5:49 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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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