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()"
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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