Re: [Qemu-devel] [PATCH 02/11] block/io: add bdrv_co_write_compressed

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

On 28.06.2016 14:09, Kevin Wolf wrote:
> Am 31.05.2016 um 11:15 hat Denis V. Lunev geschrieben:
>> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
>>
>> This patch just adds the interface to the bdrv_co_pwritev_compressed,
>> which is currently not used but will be useful for safe implementation of the
>> bdrv_co_write_compressed callback in format drivers.
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Jeff Cody <jcody@redhat.com>
>> CC: Markus Armbruster <armbru@redhat.com>
>> CC: Eric Blake <eblake@redhat.com>
>> CC: John Snow <jsnow@redhat.com>
>> CC: Stefan Hajnoczi <stefanha@redhat.com>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> ---
>>   block/io.c                | 78 +++++++++++++++++++++++++++++++++++++++++++----
>>   include/block/block_int.h |  5 +++
>>   qemu-img.c                |  2 +-
>>   3 files changed, 78 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/io.c b/block/io.c
>> index c5bb6ae..54cd9a4 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -1779,8 +1779,8 @@ int bdrv_is_allocated_above(BlockDriverState *top,
>>       return 0;
>>   }
>>
>> -int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
>> -                           const void *buf, int count)
>> +int coroutine_fn bdrv_co_pwritev_compressed(BlockDriverState *bs,
>> +    int64_t offset, unsigned int bytes, QEMUIOVector *qiov)
>>   {
>>       BlockDriver *drv = bs->drv;
>>       int ret;
>> @@ -1788,18 +1788,84 @@ int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
>>       if (!drv) {
>>           return -ENOMEDIUM;
>>       }
>> -    if (!drv->bdrv_write_compressed) {
>> +
>> +    if (!drv->bdrv_co_write_compressed) {
>>           return -ENOTSUP;
>>       }
>> -    ret = bdrv_check_byte_request(bs, offset, count);
>> +
>> +    ret = bdrv_check_byte_request(bs, offset, bytes);
>>       if (ret < 0) {
>>           return ret;
>>       }
>>
>>       assert(QLIST_EMPTY(&bs->dirty_bitmaps));
>> +    assert(qemu_in_coroutine());
>> +
>> +    return drv->bdrv_co_write_compressed(bs, offset >> BDRV_SECTOR_BITS,
>> +                                         bytes >> BDRV_SECTOR_BITS, qiov);
>> +}
>> +
>> +typedef struct BdrvWriteCompressedCo {
>> +    BlockDriverState *bs;
>> +    int64_t offset;
>> +    QEMUIOVector *qiov;
>> +    int ret;
>> +} BdrvWriteCompressedCo;
>
> I think you could just reuse RwCo here.
>

I reused BlkRwCo, and it's only a temporary change.

> And in fact, this made we wonder whether we can reuse more from the
> normal I/O path. If compressed writes could be made just another REQ_*
> flag and we went through bdrv_co_pwritev(), we would automatically get
> the alignment code if we don't want to convert drivers to byte-based.
> And also the existing coroutine wrapper code would be reused instead
> implementing it once more.
>
> I'm not completely sure how special compressed writes really are, so
> reusing the normal I/O path may or may not work. It might be worth
> investigating, though.
>
>> --- a/include/block/block_int.h
>> +++ b/include/block/block_int.h
>> @@ -207,6 +207,9 @@ struct BlockDriver {
>>       int (*bdrv_write_compressed)(BlockDriverState *bs, int64_t sector_num,
>>                                    const uint8_t *buf, int nb_sectors);
>>
>> +    int coroutine_fn (*bdrv_co_write_compressed)(BlockDriverState *bs,
>> +        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
>
> This should be called bdrv_co_writev_compressed because it's a vectored
> interface.
>
agree

> Kevin
>