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 <jeff.liu at oracle.com>
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 <wb at munzinger.de>
Cc: Mark Fashen <mfasheh at suse.de>
Cc: Joel Becker <jlbec at evilplan.org>
Signed-off-by: Jie Liu <jeff.liu at oracle.com>
---
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
>
>
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