From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:33172 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751476AbcGOCXH (ORCPT ); Thu, 14 Jul 2016 22:23:07 -0400 Subject: Re: [PATCH] Btrfs-progs: fix btrfs-map-logical to only print extent mapping info To: Liu Bo , References: <1468546827-28501-1-git-send-email-bo.li.liu@oracle.com> CC: David Sterba From: Qu Wenruo Message-ID: Date: Fri, 15 Jul 2016 10:22:52 +0800 MIME-Version: 1.0 In-Reply-To: <1468546827-28501-1-git-send-email-bo.li.liu@oracle.com> Content-Type: text/plain; charset="utf-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: At 07/15/2016 09:40 AM, Liu Bo wrote: > I have a valid btrfs image which contains, > ... > item 10 key (1103101952 BLOCK_GROUP_ITEM 1288372224) itemoff 15947 itemsize 24 > block group used 655360 chunk_objectid 256 flags DATA|RAID5 > item 11 key (1103364096 EXTENT_ITEM 131072) itemoff 15894 itemsize 53 > extent refs 1 gen 11 flags DATA > extent data backref root 5 objectid 258 offset 0 count 1 > item 12 key (1103888384 EXTENT_ITEM 262144) itemoff 15841 itemsize 53 > extent refs 1 gen 15 flags DATA > extent data backref root 1 objectid 256 offset 0 count 1 > item 13 key (1104281600 EXTENT_ITEM 262144) itemoff 15788 itemsize 53 > extent refs 1 gen 15 flags DATA > extent data backref root 1 objectid 257 offset 0 count 1 > ... > > The extent [1103364096, 131072) has length 131072, but if we run > > "btrfs-map-logical -l 1103364096 -b $((65536 * 3)) /dev/sda" > > it will return mapping info 's of non-existing extents. > > It's because it assumes that extents's are contiguous on logical address, > when it's not true, after one loop (cur_logical += cur_len) and mapping > the next extent, we can get an extent that is out of our search range and > we end up with a negative @real_len and printing all mapping infos till > the disk end. > > Signed-off-by: Liu Bo Reviewed-by: Qu Wenruo Yes, the assumption of all extents are contiguous is quite wrong. So your check is needed. Thanks, Qu > --- > btrfs-map-logical.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/btrfs-map-logical.c b/btrfs-map-logical.c > index fd0286d..f421a50 100644 > --- a/btrfs-map-logical.c > +++ b/btrfs-map-logical.c > @@ -329,6 +329,11 @@ int main(int argc, char **argv) > goto out_close_fd; > if (ret > 0) > break; > + /* check again if there is overlap. */ > + if (cur_logical + cur_len < logical || > + cur_logical >= logical + bytes) > + break; > + > real_logical = max(logical, cur_logical); > real_len = min(logical + bytes, cur_logical + cur_len) - > real_logical; >