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Re: [PATCH v2] xfstests:Make 225 compare map and fiemap at each block.

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH v2] xfstests:Make 225 compare map and fiemap at each block.
From: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
Date: Sun, 22 May 2011 20:38:27 +0800
Cc: josef@xxxxxxxxxx, sandeen@xxxxxxxxxx, xfs@xxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx
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In-reply-to: <20110519111205.GI32466@dastard>
References: <1305789665-32743-1-git-send-email-xiaoqiangnk@xxxxxxxxx> <20110519111205.GI32466@dastard>
Hi Dave,

Thank you for your review.  I will resend it.

On Thu, May 19, 2011 at 7:12 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Thu, May 19, 2011 at 03:21:05PM +0800, Yongqiang Yang wrote:
>> Due to my carelessness, I induced a ugly patch to ext4's fiemap, but
>> 225 could not find it.  So I looked into the 225 and could not figure out
>> logic in compare_map_and_fiemap(), which seemed to mix extents with
>> blocks.  Then I made 225 compare map and fiemap at each block, the new
>> 225 can find another bug in ext4 with 1k block.
>>
>> The new 225 works well on ext3, ext4 and xfs with both 1K and 4K block.
>
> The change log could do with some work. What cases did 225 not
> cover, what new cases does it cover, what are the impacts of the
> change, what bugs were fixed, etc. "I didn't understand the existing
> code so I rewrote it" isn't very useful to someone trying to
> understand why the changes were made in a couple of years time....
>
>>
>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
>> ---
>> v1->v2:
>> Josef <josef@xxxxxxxxxx> reviewed the v1 patch and pointed out the bug which
>> made xfs not work and several coding styles.
>>
>> According to reply from Josef, I
>>  fixed the bug which added ';' after an if statement.
>>  removed the trailing whitespace.
>>
>> Apart from things above, I
>>  made check_weird_fs_hole() verify bytes read by pread().
>>
>>  src/fiemap-tester.c |  251 
>> ++++++++++++++++++++++++++++-----------------------
>>  1 files changed, 140 insertions(+), 111 deletions(-)
>>
>> diff --git a/src/fiemap-tester.c b/src/fiemap-tester.c
>> index 1663f84..319a9bb 100644
>> --- a/src/fiemap-tester.c
>> +++ b/src/fiemap-tester.c
>> @@ -14,6 +14,9 @@
>>   * You should have received a copy of the GNU General Public License
>>   * along with this program; if not, write the Free Software Foundation,
>>   * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
>> + *
>> + * Compare map and fiemap at each block,
>> + * Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>, 2011
>>   */
>
> Changelogs belong in the repository commit message, not the code.
>
>>  #include <stdio.h>
>> @@ -57,7 +60,7 @@ generate_file_mapping(int blocks, int prealloc)
>>       int num_types = 2, cur_block = 0;
>>       int i = 0;
>>
>> -     map = malloc(sizeof(char) * blocks);
>> +     map = malloc(sizeof(char) * (blocks + 1));
>
> What is the bug this is fixing? Nothing in the change log tells me
> why this is being done....
>
>>       if (!map)
>>               return NULL;
>>
>> @@ -81,6 +84,7 @@ generate_file_mapping(int blocks, int prealloc)
>>               cur_block++;
>>       }
>>
>> +     map[blocks] = 0;
>
> Why is this necessary?
If there are any errors,  map is printed out as a string.
>
>>       return map;
>>  }
>>
>> @@ -247,55 +251,36 @@ check_flags(struct fiemap *fiemap, int blocksize)
>>  }
>>
>>  static int
>> -check_data(struct fiemap *fiemap, __u64 logical_offset, int blocksize,
>> +check_data(struct fiemap_extent *extent ,  __u64 logical_offset, int 
>> blocksize,
>>          int last, int prealloc)
>
> Perhaps adding a comment explaing what the function is actually
> checking is in order seeing as you just changed it...
>
> ....
>> @@ -306,7 +291,7 @@ static int
>>  check_weird_fs_hole(int fd, __u64 logical_offset, int blocksize)
>>  {
>>       static int warning_printed = 0;
>> -     int block, i;
>> +     int block, i, count;
>>       size_t buf_len = sizeof(char) * blocksize;
>>       char *buf;
>>
>> @@ -330,15 +315,16 @@ check_weird_fs_hole(int fd, __u64 logical_offset, int 
>> blocksize)
>>               return -1;
>>       }
>>
>> -     if (pread(fd, buf, buf_len, (off_t)logical_offset) < 0) {
>> +     count = pread(fd, buf, buf_len, (off_t)logical_offset);
>> +     if (count < 0) {
>>               perror("Error reading from file");
>>               free(buf);
>>               return -1;
>>       }
>>
>> -     for (i = 0; i < buf_len; i++) {
>> +     for (i = 0; i < count; i++) {
>
> What bug in the test is this fixing?  Surely a short read indicates
> a filesystem problem? Only checking the bytes returned instead of
> the entire hole region will hide the fact that the read didn't cover
> the range that was asked for and so we haven't validated the entire
> region we were supposed to...
I think read operation is verified in other tests, XFS has blocks
after the size, so I rely on read bytes.
>
>> @@ -370,35 +356,25 @@ check_weird_fs_hole(int fd, __u64 logical_offset, int 
>> blocksize)
>>  }
>>
>>  static int
>> -check_hole(struct fiemap *fiemap, int fd, __u64 logical_offset, int 
>> blocksize)
>> +check_hole(struct fiemap_extent *extent, int fd, __u64 logical_offset,
>> +        int blocksize)
>>  {
>
> Same issue with adding a comment explaining what is being
> checked....
>
>> -     struct fiemap_extent *extent;
>> -     int c;
>> +     __u64 start, end;
>>
>> -     for (c = 0; c < fiemap->fm_mapped_extents; c++) {
>> -             __u64 start, end;
>> -             extent = &fiemap->fm_extents[c];
>> -
>> -             start = extent->fe_logical;
>> -             end = extent->fe_logical + extent->fe_length;
>> -
>> -             if (logical_offset > end)
>> -                     continue;
>> -             if (logical_offset + blocksize < start)
>> -                     break;
>> +     start = extent->fe_logical;
>> +     end = extent->fe_logical + extent->fe_length;
>>
>> -             if (logical_offset >= start &&
>> -                 logical_offset < end) {
>> +     if (logical_offset >= start &&
>> +         logical_offset < end) {
>>
>> -                     if (check_weird_fs_hole(fd, logical_offset,
>> -                                             blocksize) == 0)
>> -                             break;
>> +             if (check_weird_fs_hole(fd, logical_offset,
>> +                                     blocksize) == 0)
>> +                     return 0;
>
>                error = check_weird_fs_hole(fd, logical_offset,
>                                                blocksize);
>                if (error == 0)
>                        return 0;
>
>> @@ -423,9 +399,11 @@ compare_fiemap_and_map(int fd, char *map, int blocks, 
>> int blocksize, int syncfil
>>  {
>>       struct fiemap *fiemap;
>>       char *fiebuf;
>> -     int blocks_to_map, ret, cur_extent = 0, last_data;
>> +     int blocks_to_map, ret, last_data = -1;
>>       __u64 map_start, map_length;
>>       int i, c;
>> +     int cur_block = 0;
>> +     int last_found = 0;
>>
>>       if (query_fiemap_count(fd, blocks, blocksize) < 0)
>>               return -1;
>> @@ -451,8 +429,11 @@ compare_fiemap_and_map(int fd, char *map, int blocks, 
>> int blocksize, int syncfil
>>       fiemap->fm_extent_count = blocks_to_map;
>>       fiemap->fm_mapped_extents = 0;
>>
>> +     /* check fiemap by looking at each block. */
>>       do {
>> -             fiemap->fm_start = map_start;
>> +             int nr_extents;
>> +
>> +             fiemap->fm_start = cur_block * blocksize;
>>               fiemap->fm_length = map_length;
>>
>>               ret = ioctl(fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
>> @@ -465,45 +446,93 @@ compare_fiemap_and_map(int fd, char *map, int blocks, 
>> int blocksize, int syncfil
>>               if (check_flags(fiemap, blocksize))
>>                       goto error;
>>
>> -             for (i = cur_extent, c = 1; i < blocks; i++, c++) {
>> -                     __u64 logical_offset = i * blocksize;
>> -
>> -                     if (c > fiemap->fm_mapped_extents) {
>> -                             i++;
>> -                             break;
>> +             nr_extents = fiemap->fm_mapped_extents;
>> +             if (nr_extents == 0) {
>> +                     int block = cur_block + (map_length - 1) / blocksize;
>> +                     for (; cur_block <= block &&
>> +                            cur_block < blocks; cur_block++) {
>> +                             /* check hole */
>> +                             if (map[cur_block] != 'H') {
>> +                                     printf("ERROR: map[%d] should not be "
>> +                                            "a hole\n", cur_block);
>> +                                     goto error;
>> +                             }
>>                       }
>> +                     continue;
>> +             }
>>
>> -                     switch (map[i]) {
>> -                     case 'D':
>> -                             if (check_data(fiemap, logical_offset,
>> -                                            blocksize, last_data == i, 0))
>> +             for (c = 0; c < nr_extents; c++) {
>> +                     __u64 offset;
>> +                     int block;
>> +                     struct fiemap_extent *extent;
>> +
>> +
>> +                     extent = &fiemap->fm_extents[c];
>> +                     offset = extent->fe_logical;
>> +                     block = offset / blocksize;
>> +
>> +                     /* check hole. */
>> +                     for (; cur_block < block && cur_block < blocks;
>> +                          cur_block++) {
>> +                             if (map[cur_block] != 'H') {
>> +                                     printf("ERROR: map[%d] should not be "
>> +                                            "a hole\n", cur_block);
>>                                       goto error;
>> -                             break;
>> -                     case 'H':
>> -                             if (check_hole(fiemap, fd, logical_offset,
>> -                                            blocksize))
>> +                             }
>> +                     }
>> +
>> +                     offset = extent->fe_logical + extent->fe_length;
>> +                     block = offset / blocksize;
>> +                     /* check data */
>> +                     for (; cur_block < block && cur_block < blocks;
>> +                          cur_block++) {
>> +                             int last;
>> +                             offset = (__u64)cur_block * blocksize;
>> +                             last = (cur_block == last_data);
>> +                             last_found = last_found ? last_found : last;
>> +                             switch (map[cur_block]) {
>> +                             case 'D':
>> +                                     if (check_data(extent, offset,
>> +                                                    blocksize, last, 0))
>> +                                             goto error;
>> +                                     break;
>> +                             case 'H':
>> +                                     if (check_hole(extent, fd, offset,
>> +                                                    blocksize))
>> +                                             goto error;
>> +                                     break;
>> +
>> +                             case 'P':
>> +                                     if (check_data(extent, offset,
>> +                                                    blocksize, last, 1))
>> +                                             goto error;
>> +                                     break;
>> +                             default:
>> +                                     printf("ERROR: weird value in "
>> +                                            "map: %c\n", map[i]);
>>                                       goto error;
>> -                             break;
>> -                     case 'P':
>> -                             if (check_data(fiemap, logical_offset,
>> -                                            blocksize, last_data == i, 1))
>> +                             }
>> +                     }
>> +
>> +                     for (; cur_block < block; cur_block++) {
>> +                             offset = (__u64)cur_block * blocksize;
>> +                             if (check_hole(extent, fd, offset, blocksize))
>>                                       goto error;
>> -                             break;
>> -                     default:
>> -                             printf("ERROR: weird value in map: %c\n",
>> -                                    map[i]);
>> -                             goto error;
>>                       }
>>               }
>> -             cur_extent = i;
>> -             map_start = i * blocksize;
>> -     } while (cur_extent < blocks);
>> +     } while (cur_block < blocks);
>>
>> -     ret = 0;
>> -     return ret;
>> +     if (!last_found && last_data != -1) {
>> +             printf("ERROR: find no last extent\n");
>> +             goto error;
>> +     }
>> +
>> +     free(fiebuf);
>> +     return 0;
>>  error:
>>       printf("map is '%s'\n", map);
>>       show_extents(fiemap, blocksize);
>> +     free(fiebuf);
>>       return -1;
>>  }
>
> I can't say I like this - the previous way of iterating the map and
> checking that the overlapping fiemap extent is of the correct type
> seems much simpler to me.
>
> Your code now has to special case fiemaps with nr_extents == 0, has
> to handle holes separately both before and after data extents and
> adds a bunch of duplicated code. I find it much harder to follow,
> and I don't see how rewriting the code like this makes the test
> better. Especially as it doesn't tell me what the problems with the
> original code were that you've supposedly fixed...
I could not figure out logic in old code comparing fiemap and map,
I will update the changelog.
>
>>
>> @@ -605,6 +634,18 @@ main(int argc, char **argv)
>>               printf("Starting infinite run, if you don't see any output "
>>                      "then its working properly.\n");
>>       do {
>> +             if (ftruncate(fd, 0)) {
>> +                     perror("Could not truncate file\n");
>> +                     close(fd);
>> +                     exit(1);
>> +             }
>> +
>> +             if (lseek(fd, 0, SEEK_SET)) {
>> +                     perror("Could not seek set\n");
>> +                     close(fd);
>> +                     exit(1);
>> +             }
>> +
>>               if (!map) {
>>                       blocks = random() % maxblocks;
>>                       if (blocks == 0) {
>> @@ -639,18 +680,6 @@ main(int argc, char **argv)
>>               free(map);
>>               map = NULL;
>>
>> -             if (ftruncate(fd, 0)) {
>> -                     perror("Could not truncate file\n");
>> -                     close(fd);
>> -                     exit(1);
>> -             }
>> -
>> -             if (lseek(fd, 0, SEEK_SET)) {
>> -                     perror("Could not seek set\n");
>> -                     close(fd);
>> -                     exit(1);
>> -             }
>> -
>>               if (runs) runs--;
>>       } while (runs != 0);
>
> What bug is this fixing? There's Nothing in the changelog....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
>



-- 
Best Wishes
Yongqiang Yang

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