Commit f76889e7 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Stefan Hajnoczi
Browse files

util/iov: improve qemu_iovec_is_zero 



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: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190604161514.262241-3-vsementsov@virtuozzo.com
Message-Id: <20190604161514.262241-3-vsementsov@virtuozzo.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent d953169d

block/io.c

+1 −1
Original line number Diff line number Diff line
@@ -1722,7 +1722,7 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child, 


    if (!ret && bs->detect_zeroes != BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF &&

        !(flags & BDRV_REQ_ZERO_WRITE) && drv->bdrv_co_pwrite_zeroes &&

        qemu_iovec_is_zero(qiov)) {

        qemu_iovec_is_zero(qiov, 0, qiov->size)) {

        flags |= BDRV_REQ_ZERO_WRITE;

        if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) {

            flags |= BDRV_REQ_MAY_UNMAP;

include/qemu/iov.h

+1 −1
Original line number Diff line number Diff line
@@ -212,7 +212,7 @@ void qemu_iovec_concat(QEMUIOVector *dst, 
size_t qemu_iovec_concat_iov(QEMUIOVector *dst,

                             struct iovec *src_iov, unsigned int src_cnt,

                             size_t soffset, size_t sbytes);

bool qemu_iovec_is_zero(QEMUIOVector *qiov);

bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t qiov_offeset, size_t bytes);

void qemu_iovec_destroy(QEMUIOVector *qiov);

void qemu_iovec_reset(QEMUIOVector *qiov);

size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,

util/iov.c

+19 −12
Original line number Diff line number Diff line
@@ -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)) {

            return false;

        }

        for (; offs < qiov->iov[i].iov_len; offs++) {

            if (ptr[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;

        }



        current_offset = 0;

        bytes -= len;

        iov++;

    }

    }



    return true;

}