linux-kernel - Re: [PATCH RFC] vfs: add a O

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Message-ID: <CAFLxGvw8ESrM6vZ4iB70JFQN-qR-Trs3j1O_+y36tSOn0GVH4A@mail.gmail.com>
Date:	Thu, 7 May 2015 21:09:58 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Zach Brown <zab@...hat.com>
Cc:	Dave Chinner <david@...morbit.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Sage Weil <sweil@...hat.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>
Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag

On Thu, May 7, 2015 at 7:20 PM, Zach Brown <zab@...hat.com> wrote:
> On Thu, May 07, 2015 at 10:26:17AM +1000, Dave Chinner wrote:
>> On Wed, May 06, 2015 at 03:00:12PM -0700, Zach Brown wrote:
>> > Add the O_NOMTIME flag which prevents mtime from being updated which can
>> > greatly reduce the IO overhead of writes to allocated and initialized
>> > regions of files.
>>
>> Hmmm. How do backup programs now work out if the file has changed
>> and hence needs copying again? ie. applications using this will
>> break other critical infrastructure in subtle ways.
>
> By using backup infrastructure that doesn't use cmtime.  Like btrfs
> send/recv.  Or application level backups that know how to do
> incrementals from metadata in giant database files, say, without
> walking, comparing, and copying the entire thing.

But how can Joey random user know that some of his
applications are using O_NOMTIME and his KISS backup
program does no longer function as expected?

-- 
Thanks,
//richard
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