Victor Latushkin wrote:
> On Apr 18, 2011, at 11:22 AM, jeff.liu wrote:
>
>> Hello List,
>>
>> I am trying to fetch the data/hole info of a sparse file through the
>> lseek(SEEK_HOLE/SEEK_DATA)
>> stuff, the result of fpathconf(..., _PC_MIN_HOLE_SIZE) is ok, so I think
>> this interface is supported
>> on my testing ZFS, but SEEK_HOLE always return the sparse file total size
>> instead of the desired
>> first hole start offset.
>>
>> The whole process was shown as following, Could anyone give any hints?
>>
>> Create a sparse file("sparse2") as below, SEEK_HOLE should returns *ZERO*
>> and SEEK_DATA should
>> returns 40960 IMHO:
>> bash-3.00@ python -c "f=open('sparse2', 'w'); f.seek(40960); f.write('BYE');
>> f.close()"
>
> With default settings you'll get single-block file without any holes from ZFS
> perspective.
>
> Try somewhat bigger sparse file like this:
>
> dd if=/dev/urandom of=test.file count=1 bs=128k oseek=1024
Thanks for your quick response! It works for me now.
Regards,
-Jeff
>
>
>> A tiny program to examine the hole start offset of file "sparse2".
>> #include <stdio.h>
>> #include <string.h>
>> #include <fcntl.h>
>> #include <sys/stat.h>
>> #include <sys/types.h>
>> #include <unistd.h>
>> #include <errno.h>
>>
>> int
>> main(int argc, char *argv[])
>> {
>> int ret = 0, fd;
>> off_t data_pos, hole_pos;
>> const char *filename = NULL;
>>
>> if (argc != 2) {
>> fprintf(stderr, "Usage: %s file\n", argv[0]);
>> return 1;
>> }
>>
>> filename = strdup(argv[1]);
>> if (!filename) {
>> perror("strdup");
>> return -1;
>> }
>>
>> fd = open(filename, O_RDONLY);
>> if (fd < 0) {
>> perror("open");
>> ret = -1;
>> goto out;
>> }
>>
>> if (fpathconf(fd, _PC_MIN_HOLE_SIZE) < 0) {
>> fprintf(stderr, "The underlying filesystem does not support
>> SEEK_HOLE.\n");
>> goto out;
>> }
>>
>> hole_pos = lseek(fd, (off_t)0, SEEK_HOLE);
>> if (hole_pos < 0) {
>> if (errno == EINVAL || errno == ENOTSUP) {
>> fprintf(stderr, "SEEK_HOLE does not support on OS or
>> filesystem.\n");
>> goto out;
>> }
>>
>> perror("lseek");
>> ret = -1;
>> goto out;
>> }
>>
>> if (hole_pos == 0)
>> fprintf(stderr, "Oh, no!! hole start at offset 0?\n");
>>
>> if (hole_pos > 0)
>> fprintf(stderr, "detected a real hole at: %d.\n", hole_pos);
>>
>> out:
>> free(filename);
>> lseek(fd, (off_t)0, SEEK_SET);
>>
>> return 0;
>> }
>>
>> My test env:
>> ============
>> bash-3.00# uname -a
>> SunOS unknown 5.10 Generic_142910-17 i86pc i386 i86pc
>>
>> man zfs(1):
>> SunOS 5.10 Last change: 11 Jun 2010
>>
>> bash-3.00# zfs list
>> NAME USED AVAIL REFER MOUNTPOINT
>> ...
>> ...
>> rpool/export/home 120K 139G 120K /export/home
>> ...
>>
>> "sparse2" located at "/export/home":
>> bash-3.00# zdb -dddddd rpool/export/home
>> Object lvl iblk dblk dsize lsize %full type
>> 104 1 16K 40.5K 40.5K 40.5K 100.00 ZFS plain file
>> 264 bonus ZFS znode
>> dnode flags: USED_BYTES USERUSED_ACCOUNTED
>> dnode maxblkid: 0
>> path /sparse2
>> uid 0
>> gid 0
>> atime Mon Apr 18 14:50:46 2011
>> mtime Mon Apr 18 14:50:46 2011
>> ctime Mon Apr 18 14:50:46 2011
>> crtime Mon Apr 18 14:50:46 2011
>> gen 497
>> mode 100600
>> size 40963
>> parent 3
>> links 1
>> xattr 0
>> rdev 0x0000000000000000
>> Indirect blocks:
>> 0 L0 0:1960ce000:a200 a200L/a200P F=1 B=497/497
>>
>> segment [0000000000000000, 000000000000a200) size 40.5K
>>
>> bash-3.00# zdb -R rpool/export/home 0:1960ce000:a200
>> .....
>> 009ff0: 0000000000000000 0000000000000000 ................
>> 00a000: 0000000000455942 0000000000000000 BYE.............
>> 00a010: 0000000000000000 0000000000000000 ................
>> ....
>> ...
>>
>> Any comments are appreciated!
>>
>> Thanks,
>> -Jeff
>> _______________________________________________
>> zfs-discuss mailing list
>> zfs-discuss@opensolaris.org
>> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
>
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