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cutils: extract buffer_is_zero() from qemu-img.c

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The qemu-img.c:is_not_zero() function checks if a buffer contains all
zeroes.  This function will come in handy for zero-detection in the
block layer, so clean it up and move it to cutils.c.

Note that the function now returns true if the buffer is all zeroes.
This avoids the double-negatives (i.e. !is_not_zero()) that the old
function can cause in callers.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2012-02-07 13:27:24 +00:00 • committed by Kevin Wolf
parent 7a65c8cc31
commit 1a6d39fd71
3 changed files with 44 additions and 39 deletions
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46
qemu-img.c
View file

@ -514,40 +514,6 @@ static int img_commit(int argc, char **argv)
return 0;
}
/*
* Checks whether the sector is not a zero sector.
*
* Attention! The len must be a multiple of 4 * sizeof(long) due to
* restriction of optimizations in this function.
*/
static int is_not_zero(const uint8_t *sector, int len)
{
/*
* Use long as the biggest available internal data type that fits into the
* CPU register and unroll the loop to smooth out the effect of memory
* latency.
*/
int i;
long d0, d1, d2, d3;
const long * const data = (const long *) sector;
len /= sizeof(long);
for(i = 0; i < len; i += 4) {
d0 = data[i + 0];
d1 = data[i + 1];
d2 = data[i + 2];
d3 = data[i + 3];
if (d0 || d1 || d2 || d3) {
return 1;
}
}
return 0;
}
/*
* Returns true iff the first sector pointed to by 'buf' contains at least
* a non-NUL byte.
@ -557,20 +523,22 @@ static int is_not_zero(const uint8_t *sector, int len)
*/
static int is_allocated_sectors(const uint8_t *buf, int n, int *pnum)
{
int v, i;
bool is_zero;
int i;
if (n <= 0) {
*pnum = 0;
return 0;
}
v = is_not_zero(buf, 512);
is_zero = buffer_is_zero(buf, 512);
for(i = 1; i < n; i++) {
buf += 512;
if (v != is_not_zero(buf, 512))
if (is_zero != buffer_is_zero(buf, 512)) {
break;
}
}
*pnum = i;
return v;
return !is_zero;
}
/*
@ -955,7 +923,7 @@ static int img_convert(int argc, char **argv)
if (n < cluster_sectors) {
memset(buf + n * 512, 0, cluster_size - n * 512);
}
if (is_not_zero(buf, cluster_size)) {
if (!buffer_is_zero(buf, cluster_size)) {
ret = bdrv_write_compressed(out_bs, sector_num, buf,
cluster_sectors);
if (ret != 0) {