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
>
> 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
> _______________________________________________
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> zfs-discuss@opensolaris.org
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