Am 07.10.2013 um 10:29 schrieb Stefan Hajnoczi <stefa...@gmail.com>:
> On Tue, Sep 24, 2013 at 03:35:02PM +0200, Peter Lieven wrote:
>> @@ -4245,7 +4250,37 @@ int coroutine_fn bdrv_co_discard(BlockDriverState
>> *bs, int64_t sector_num,
>> }
>>
>> if (bs->drv->bdrv_co_discard) {
>> - return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
>> + int max_discard = bs->bl.max_discard ?
>> + bs->bl.max_discard : MAX_DISCARD_DEFAULT;
>> +
>> + while (nb_sectors > 0) {
>> + int ret;
>> + int num = nb_sectors;
>> +
>> + /* align request */
>> + if (bs->bl.discard_alignment &&
>> + num >= bs->bl.discard_alignment &&
>> + sector_num % bs->bl.discard_alignment) {
>> + if (num > bs->bl.discard_alignment) {
>> + num = bs->bl.discard_alignment;
>> + }
>> + num -= sector_num % bs->bl.discard_alignment;
>> + }
>
> Is it always possible to discard at arbitrary sector offsets?
It should be. This just makes sure that the unaligned part of a request gets
executed first (eventually resulting in an -ENOTSUP) and
consecutive calls are aligned.
For example. The alignment is 1MB (2048 sectors) and max_discard its 2048
sectors as well.. Lets say you want to discard 4096 sectors starting at offset
1024.
Then there will be 3 calls
1) discard at 1024, len 1024
2) discard at 2048, len 2048
3) discard at 4096, len 1024.
Peter
