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util/iov: improve qemu_iovec_is_zero

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We'll need to check a part of qiov soon, so implement it now.

Optimization with align down to 4 * sizeof(long) is dropped due to:
1. It is strange: it aligns length of the buffer, but where is a
   guarantee that buffer pointer is aligned itself?
2. buffer_is_zero() is a better place for optimizations and it has
   them.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190604161514.262241-3-vsementsov@virtuozzo.com
Message-Id: <20190604161514.262241-3-vsementsov@virtuozzo.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2019-06-04 19:15:04 +03:00 • committed by Stefan Hajnoczi
parent d953169d48
commit f76889e7b9
3 changed files with 21 additions and 14 deletions
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31
util/iov.c
View file

@ -451,23 +451,30 @@ void qemu_iovec_init_extended(
}
/*
* Check if the contents of the iovecs are all zero
* Check if the contents of subrange of qiov data is all zeroes.
*/
bool qemu_iovec_is_zero(QEMUIOVector *qiov)
bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t offset, size_t bytes)
{
int i;
for (i = 0; i < qiov->niov; i++) {
size_t offs = QEMU_ALIGN_DOWN(qiov->iov[i].iov_len, 4 * sizeof(long));
uint8_t *ptr = qiov->iov[i].iov_base;
if (offs && !buffer_is_zero(qiov->iov[i].iov_base, offs)) {
struct iovec *iov;
size_t current_offset;
assert(offset + bytes <= qiov->size);
iov = iov_skip_offset(qiov->iov, offset, &current_offset);
while (bytes) {
uint8_t *base = (uint8_t *)iov->iov_base + current_offset;
size_t len = MIN(iov->iov_len - current_offset, bytes);
if (!buffer_is_zero(base, len)) {
return false;
}
for (; offs < qiov->iov[i].iov_len; offs++) {
if (ptr[offs]) {
return false;
}
}
current_offset = 0;
bytes -= len;
iov++;
}
return true;
}