From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Weinberger Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag Date: Thu, 7 May 2015 21:09:58 +0200 Message-ID: References: <1430949612-21356-1-git-send-email-zab@redhat.com> <20150507002617.GJ4327@dastard> <20150507172053.GA659@lenny.home.zabbo.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Dave Chinner , Alexander Viro , Sage Weil , linux-fsdevel , LKML , "open list:ABI/API" To: Zach Brown Return-path: In-Reply-To: <20150507172053.GA659-fypN+1c5dIyjpB87vu3CluTW4wlIGRCZ@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 7, 2015 at 7:20 PM, Zach Brown 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