Am 19.09.2013 um 22:07 schrieb Eric Blake <[email protected]>:
> On 09/17/2013 07:48 AM, Peter Lieven wrote:
>> Signed-off-by: Peter Lieven <[email protected]>
>> ---
>> 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
