From: Eric Sandeen Subject: Re: bug#6131: [PATCH]: fiemap support for efficient sparse file copy Date: Fri, 11 Jun 2010 09:03:29 -0500 Message-ID: <4C124231.7020304@redhat.com> References: <4BE41FFF.4020809@oracle.com> <871vdho68j.fsf@meyering.net> <4BEC0BCC.3080906@oracle.com> <87k4qyl6lw.fsf@meyering.net> <4BF683CC.3060407@oracle.com> <4BF6ABE7.3020600@oracle.com> <877hmpeivx.fsf@meyering.net> <4BFF763A.9010205@oracle.com> <8763286kni.fsf@meyering.net> <4C0275FA.1030901@oracle.com> <874ohpywri.fsf@meyering.net> <87y6exuc5i.fsf@meyering.net> <874ohdu5b8.fsf@meyering.net> <87eighs1t9.fsf@meyering.net> <4C0FA93C.6020205@oracle.com> <87iq5sp7eg.fsf@meyering.net> <4C108CB9.8010805@oracle.com> <4C11798B.6090500@cs.ucla.edu> <4C1183FD.9010502@oracle.com> <4C11F451.8040304@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Sunil Mushran , Paul Eggert , Jim Meyering , bug-coreutils@gnu.org, Joel Becker , Chris Mason , "linux-ext4@vger.kernel.org" , Tao Ma To: "jeff.liu" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:48863 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750861Ab0FKODo (ORCPT ); Fri, 11 Jun 2010 10:03:44 -0400 In-Reply-To: <4C11F451.8040304@oracle.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: jeff.liu wrote: > Sunil Mushran wrote: >> On 06/10/2010 04:47 PM, Paul Eggert wrote: >>> On 06/09/2010 11:56 PM, jeff.liu wrote: >>> >>>> Yeah, I just realized that the behaviour I observed is caused by the >>>> delay allocation mechanism of >>>> the particular FS. >>>> >>> If the file system is using delayed allocation, then can >>> the fiemap ioctl tell us that a file contains a hole (because nothing >>> has been >>> allocated there), but read() would tell us that the file contains >>> nonzero data at the same location >>> (because it's sitting in a buffer somewhere)? If so, we'd need to do >>> something like invoke >>> fdatasync() on the file before issuing the fiemap ioctl, to force >>> allocation; or perhaps >>> there's another ioctl that will do the allocation without having to >>> actually do a sync. >>> >> I guess we'll have to use FIEMAP_FLAG_SYNC. > Hi Sunil, > > Thanks for the comments. > So we can ensure the source file synced before mapping in this way. > > Hi Jim and Paul, > > How about the tiny patch below? I agree that this is needed, thanks. -Eric > From d6d619a169ff68a9a310a69d8089b9fbf83b5f91 Mon Sep 17 00:00:00 2001 > From: Jie Liu > Date: Fri, 11 Jun 2010 16:29:02 +0800 > Subject: [PATCH 1/1] copy.c: add FIEMAP_FLAG_SYNC to fiemap ioctl > > * src/copy.c (fiemap_copy): Force kernel to sync the source > file before mapping. > > Signed-off-by: Jie Liu > --- > src/copy.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/src/copy.c b/src/copy.c > index f149be4..f48c74d 100644 > --- a/src/copy.c > +++ b/src/copy.c > @@ -191,6 +191,7 @@ fiemap_copy (int src_fd, int dest_fd, size_t buf_size, > do > { > fiemap->fm_length = FIEMAP_MAX_OFFSET; > + fiemap->fm_flags = FIEMAP_FLAG_SYNC; > fiemap->fm_extent_count = count; > > /* When ioctl(2) fails, fall back to the normal copy only if it