From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Liu Date: Wed, 07 Aug 2013 22:07:19 +0800 Subject: [Ocfs2-devel] FIEMAP problem In-Reply-To: <3326454.f4rt6OEXV7@o3-3> References: <3326454.f4rt6OEXV7@o3-3> Message-ID: <52025497.1090608@oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com On 08/07/2013 05:17 PM, David Weber wrote: > Hi, > > We are trying to use OCFS2 as VM storage. After running into problems with > qemu's disk_mirror feature we now think there could be a problem with the > FIEMAP ioctl in OCFS2. > > As far as I understand the situation looks like this: > Qemu inquiries the FS if the given section of the image is already allocated > via the FIEMAP ioctl [1] > It especially checks if fm_mapped_extents is greater 0. > OCFS2 reports on sections bigger 1048576 there would be 0 mapped_extents which > is wrong. > > I extended a userspace FIEMAP util [2] a bit to specify the start and length > parameter [3] as an easier testcase. > > When we create a big file which has no holes > dd if=/dev/urandom of=/mnt/kvm-images/urandom.img bs=1M count=1000 > > We get on lower sections the expected output: > ./a.out /mnt/kvm-images/urandom.img 10000 10 > start: 2710, length: a > File /mnt/kvm-images/urandom.img has 1 extents: > # Logical Physical Length Flags > 0: 0000000000000000 0000004ca3f00000 000000000be00000 0000 > > But on sections >= 1048576 it reports there wouldn't be any extents which is > as far as I understand wrong: > ./a.out /mnt/kvm-images/urandom.img 1048576 10 > start: 100000, length: a > File /mnt/kvm-images/urandom.img has 0 extents: > # Logical Physical Length Flags Thanks for your report, looks this problem has existed over years. As a quick response, could you please try the below fix? From: Jie Liu Call fiemap ioctl(2) with given start offset as well as an desired mapping range should show extents if possible. However, we calculate the end offset of mapping via 'mapping_end -= cpos' before iterating the extent records which would cause problems, e.g, Cluster size 4096: debugfs.ocfs2 1.6.3 Block Size Bits: 12 Cluster Size Bits: 12 The extended fiemap test utility From David: https://gist.github.com/anonymous/6172331 # dd if=/dev/urandom of=/ocfs2/test_file bs=1M count=1000 # ./fiemap /ocfs2/test_file 4096 10 start: 4096, length: 10 File /ocfs2/test_file has 0 extents: # Logical Physical Length Flags ^^^^^ <-- No extents In this case, at ocfs2_fiemap(): cpos == mapping_end == 1. Hence the loop of searching extent records was not executed at all. This patch remove the in question 'mapping_end -= cpos', and loops until the cpos is larger than the mapping_end instead. # ./fiemap /ocfs2/test_file 4096 10 start: 4096, length: 10 File /ocfs2/test_file has 1 extents: # Logical Physical Length Flags 0: 0000000000000000 0000000056a01000 0000000006a00000 0000 Reported-by: David Weber Cc: Mark Fashen Cc: Joel Becker Signed-off-by: Jie Liu --- fs/ocfs2/extent_map.c | 1 - 1 file changed, 1 deletion(-) diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c index 2487116..8460647 100644 --- a/fs/ocfs2/extent_map.c +++ b/fs/ocfs2/extent_map.c @@ -781,7 +781,6 @@ int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, cpos = map_start >> osb->s_clustersize_bits; mapping_end = ocfs2_clusters_for_bytes(inode->i_sb, map_start + map_len); - mapping_end -= cpos; is_last = 0; while (cpos < mapping_end && !is_last) { u32 fe_flags; -- 1.7.9.5 > > We're running linux-3.11-rc4 plus the following patches: > [PATCH V2] ocfs2: update inode size after zeroed the hole > [PATCH RESEND] ocfs2: fix NULL pointer dereference in > ocfs2_duplicate_clusters_by_page > NULL pointer dereference at ocfs2_dir_foreach_blk_id > [patch v3] ocfs2: ocfs2: fix recent memory corruption bug > > o2info --volinfo /dev/drbd0 > Label: kvm-images > UUID: BE7C101466AD4F2196A849C7A6031263 > Block Size: 4096 > Cluster Size: 1048576 > Node Slots: 8 > Features: backup-super strict-journal-super sparse extended-slotmap > Features: inline-data xattr indexed-dirs refcount discontig-bg unwritten > > Thanks in advance! > > Cheers, > David > > > [1] http://git.qemu.org/?p=qemu.git;a=blob;f=block/raw-posix.c;h=ba721d3f5bd98a6b62791c2e20dbf2894021ad76;hb=HEAD#l1087 > > [2] http://smackerelofopinion.blogspot.de/2010/01/using-fiemap-ioctl-to-get-file-extents.html > > [3] https://gist.github.com/anonymous/6172331 > > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel at oss.oracle.com > https://oss.oracle.com/mailman/listinfo/ocfs2-devel