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Date: Tue, 7 Oct 2014 12:12:44 +0800
From: Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>
Subject: Re: [PATCH] filefrag: fix wrong extent count calculation when using
FIBMAP
Hi,
On 10/07/2014 11:59 AM, Darrick J. Wong wrote:
> On Tue, Oct 07, 2014 at 11:50:34AM +0800, Xiaoguang Wang wrote:
>> Hi,
>>
>> On 10/07/2014 10:43 AM, Darrick J. Wong wrote:
>>> On Mon, Oct 06, 2014 at 07:05:39PM +0800, Xiaoguang Wang wrote:
>>>> When using FIBMAP and '-e' option is specified, the calculation for fiemap_extent
>>>> is wrong, we wrongly updated fm_ext.fe_logical for every iteration, please see the
>>>> code in the end of 'for' loop in fm_ext.fe_logical().
>>>>
>>>> In an ext2 file system(block size is 1024 bytes),
>>>> dd if=/dev/zero of=testfile bs=1k count=15
>>>> Using debugfs, corresponding physical blocks are "2049 2050 2051 2052 2053 2054
>>>> 2055 2056 2057 2058 2059 2060 1025 2061 2062 2063", 1025 is this indirect block.
>>>> Before this patch, filefrag's output would be:
>>>> filefrag -B -e testfile
>>>> Filesystem type is: ef53
>>>> Filesystem cylinder groups approximately 16
>>>> File size of testfile is 15360 (15 blocks of 1024 bytes)
>>>> ext: logical_offset: physical_offset: length: expected: flags:
>>>> 0: 1.. 2: 2050.. 2051: 2: 2051: merged
>>>> 1: 3.. 4: 2052.. 2053: 2: 2053: merged
>>>> 2: 5.. 6: 2054.. 2055: 2: 2055: merged
>>>> 3: 7.. 8: 2056.. 2057: 2: 2057: merged
>>>> 4: 9.. 10: 2058.. 2059: 2: 2059: merged
>>>> 5: 11.. 12: 2060.. 2061: 2: 2062: merged
>>>> 6: 13.. 14: 2062.. 2063: 2: 2063: merged,eof
>>>> 7: 14.. 14: 2063.. 2063: 1: 2063: merged,eof
>>>> This output is not reasonable.
>>>
>>> It's just plain whacky. Why would logical offset 14 be listed twice? :)
>>
>> Because of the wrong code :) It updates fm_ext.fe_logical and fm_ext.fe_physical for every
>> iteration :) and i think the original code is not that readable.
>>>
>>>> Fix this bug and try to make it readable. After this patch, the output would be:
>>>> ./filefrag -B -e mntpoint/testfile
>>>> Filesystem type is: ef53
>>>> Filesystem cylinder groups approximately 16
>>>> File size of mntpoint/testfile is 15360 (15 blocks of 1024 bytes)
>>>> ext: logical_offset: physical_offset: length: expected: flags:
>>>> 0: 0.. 11: 2049.. 2060: 12: 2062: merged
>>>> 1: 12.. 14: 2061.. 2063: 3: 2063: merged,eof
>>>> mntpoint/testfile: 2 extents found, perfection would be 1 extent
>>>
>>> Where'd the indirect block end up, if not in the middle of 2049-2063?
>>
>> Indirect block's information is used to judge whether logical region is continuous physically.
>> For example, the above testfile's first indirect block is 1025, and will not shown in the output.
>
> 1025? Huh. Is this an old FS, or is there something wrong with the block
> allocator?
Yeah, it's strange. I created testfile multiple times, data blocks are basically continuous, but
indirect block always not. It seems that block allocator does not work well.
I have this test on a 128MB loop device(mkfs to ext2), OS: Fedora 19(3.9.5-301.fc19.x86_64)
Regards,
Xiaoguang Wang
>
> --D
>
>>
>>>
>>>> Signed-off-by: Xiaoguang Wang <wangxg.fnst@...fujitsu.com>
>>>> ---
>>>> misc/filefrag.c | 37 +++++++++++++++++++++++--------------
>>>> 1 file changed, 23 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/misc/filefrag.c b/misc/filefrag.c
>>>> index c1a8684..e9f7e68 100644
>>>> --- a/misc/filefrag.c
>>>> +++ b/misc/filefrag.c
>>>> @@ -315,32 +315,41 @@ static int filefrag_fibmap(int fd, int blk_shift, int *num_extents,
>>>> return rc;
>>>> if (block == 0)
>>>> continue;
>>>> + count++;
>>>> +
>>>> if (*num_extents == 0) {
>>>> (*num_extents)++;
>>>> if (force_extent) {
>>>> print_extent_header();
>>>> + fm_ext.fe_logical = logical;
>>>> fm_ext.fe_physical = block * st->st_blksize;
>>>> + fm_ext.fe_length = st->st_blksize;
>>>> }
>>>> + last_block = block;
>>>> + continue;
>>>> }
>>>> - count++;
>>>> - if (force_extent && last_block != 0 &&
>>>> - (block != last_block + 1 ||
>>>> - fm_ext.fe_logical + fm_ext.fe_length != logical)) {
>>>> - print_extent_info(&fm_ext, *num_extents - 1,
>>>> - (last_block + 1) * st->st_blksize,
>>>> - blk_shift, st);
>>>> - fm_ext.fe_length = 0;
>>>> - (*num_extents)++;
>>>> +
>>>> + if (force_extent) {
>>>> + if (block != last_block + 1 ||
>>>> + fm_ext.fe_length + fm_ext.fe_logical != logical) {
>>>> + print_extent_info(&fm_ext, *num_extents - 1,
>>>> + (last_block + 1) *
>>>> + st->st_blksize,
>>>> + blk_shift, st);
>>>> + fm_ext.fe_logical = logical;
>>>> + fm_ext.fe_physical = block * st->st_blksize;
>>>> + fm_ext.fe_length = st->st_blksize;
>>>> + (*num_extents)++;
>>>> + } else {
>>>> + fm_ext.fe_length += st->st_blksize;
>>>> + }
>>>> } else if (last_block && (block != last_block + 1)) {
>>>> - if (verbose)
>>>> + if (verbose) {
>>>> printf("Discontinuity: Block %ld is at %lu (was "
>>>> "%lu)\n", i, block, last_block + 1);
>>>> - fm_ext.fe_length = 0;
>>>> + }
>>>
>>> The { } is not needed for a single line if statement.
>>
>> OK, I'll send a new version to remove it, thanks!
>>
>> Regards,
>> Xiaoguang Wang
>>>
>>>> (*num_extents)++;
>>>> }
>>>> - fm_ext.fe_logical = logical;
>>>> - fm_ext.fe_physical = block * st->st_blksize;
>>>> - fm_ext.fe_length += st->st_blksize;
>>>> last_block = block;
>>>
>>> Otherwise, I think this looks decent.
>>>
>>> --D
>>>
>>>> }
>>>>
>>>> --
>>>> 1.8.2.1
>>>>
>>>> --
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>>> .
>>>
>>
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