Am 19.09.2013 um 22:07 schrieb Eric Blake <ebl...@redhat.com>: > On 09/17/2013 07:48 AM, Peter Lieven wrote: >> Signed-off-by: Peter Lieven <p...@kamp.de> >> --- >> block.c | 57 +++++++++++++++++++++++++++++++++++++++++---------------- >> 1 file changed, 41 insertions(+), 16 deletions(-) >> >> diff --git a/block.c b/block.c >> index 177720e..74ec342 100644 >> --- a/block.c >> +++ b/block.c >> @@ -2660,28 +2660,53 @@ static int coroutine_fn >> bdrv_co_do_write_zeroes(BlockDriverState *bs, >> BlockDriver *drv = bs->drv; >> QEMUIOVector qiov; >> struct iovec iov; >> - int ret; >> + int ret = 0; >> >> - /* TODO Emulate only part of misaligned requests instead of letting >> block >> - * drivers return -ENOTSUP and emulate everything */ >> + /* if no limit is specified in the BlockDriverState use a default >> + * of 32768 512-byte sectors (16 MiB) per request. >> + */ >> + int max_write_zeroes = bs->max_write_zeroes ? bs->max_write_zeroes : >> 32768; > > Worth having a named constant instead of a magic number?
Its the only place where it is used. I can do that, but I would keep it in front of the function rather than at the top of block.h or even in block_int.h > >> + while (nb_sectors > 0 && !ret) { > >> + >> + if (ret == -ENOTSUP) { >> + /* Fall back to bounce buffer if write zeroes is unsupported */ >> + iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE; >> + iov.iov_base = qemu_blockalign(bs, iov.iov_len); >> + memset(iov.iov_base, 0, iov.iov_len); > > This allocates, clears, and frees iov.iov_len bytes of 0 every iteration > through the loop. Can you hoist that so you only allocate the bounce > buffer once, and then clean it up after the loop completes? I can do that, but in this case, I have to allocate max_write_zeroes * BDRV_SECTOR_SIZE bytes because the iov_len might not be maximal in the first iteration due to the alignment logic. Peter