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qemu-img: Speed up comparing empty/zero images 

Two empty raw files are always compared by actually reading data even if
there is no data, because BDRV_BLOCK_ZERO is considered "allocated" in
bdrv_is_allocated_above().  That is inefficient.

Use bdrv_get_block_status_above() for more information, and skip the
consecutive zero sectors.

This brings a huge speed up in comparing sparse/empty raw images:

    $ qemu-img create a 1G

    $ time ~/build/master/bin/qemu-img compare a a
    Images are identical.

    real    0m6.583s
    user    0m0.191s
    sys     0m6.367s

    $ time qemu-img compare a a
    Images are identical.

    real    0m0.033s
    user    0m0.003s
    sys     0m0.031s

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2016-01-13 16:37:41 +08:00 committed by Kevin Wolf
parent 972b543c6b
commit 25ad8e6e95
1 changed files with 30 additions and 15 deletions
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41
qemu-img.c
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@ -1071,28 +1071,50 @@ static int img_compare(int argc, char **argv)
}
for (;;) {
int64_t status1, status2;
nb_sectors = sectors_to_process(total_sectors, sector_num);
if (nb_sectors <= 0) {
break;
}
allocated1 = bdrv_is_allocated_above(bs1, NULL, sector_num, nb_sectors,
status1 = bdrv_get_block_status_above(bs1, NULL, sector_num,
total_sectors1 - sector_num,
&pnum1);
if (allocated1 < 0) {
if (status1 < 0) {
ret = 3;
error_report("Sector allocation test failed for %s", filename1);
goto out;
}
allocated1 = status1 & BDRV_BLOCK_ALLOCATED;
allocated2 = bdrv_is_allocated_above(bs2, NULL, sector_num, nb_sectors,
status2 = bdrv_get_block_status_above(bs2, NULL, sector_num,
total_sectors2 - sector_num,
&pnum2);
if (allocated2 < 0) {
if (status2 < 0) {
ret = 3;
error_report("Sector allocation test failed for %s", filename2);
goto out;
}
nb_sectors = MIN(pnum1, pnum2);
allocated2 = status2 & BDRV_BLOCK_ALLOCATED;
if (pnum1) {
nb_sectors = MIN(nb_sectors, pnum1);
}
if (pnum2) {
nb_sectors = MIN(nb_sectors, pnum2);
}
if (allocated1 == allocated2) {
if (strict) {
if ((status1 & ~BDRV_BLOCK_OFFSET_MASK) !=
(status2 & ~BDRV_BLOCK_OFFSET_MASK)) {
ret = 1;
qprintf(quiet, "Strict mode: Offset %" PRId64
" block status mismatch!\n",
sectors_to_bytes(sector_num));
goto out;
}
}
if ((status1 & BDRV_BLOCK_ZERO) && (status2 & BDRV_BLOCK_ZERO)) {
nb_sectors = MIN(pnum1, pnum2);
} else if (allocated1 == allocated2) {
if (allocated1) {
ret = blk_read(blk1, sector_num, buf1, nb_sectors);
if (ret < 0) {
@ -1120,13 +1142,6 @@ static int img_compare(int argc, char **argv)
}
}
} else {
if (strict) {
ret = 1;
qprintf(quiet, "Strict mode: Offset %" PRId64
" allocation mismatch!\n",
sectors_to_bytes(sector_num));
goto out;
}
if (allocated1) {
ret = check_empty_sectors(blk1, sector_num, nb_sectors,