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

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

On 13.06.2016 17:32, Eric Blake wrote:
> On 05/31/2016 03:15 AM, Denis V. Lunev wrote:
>> 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)
>
> Why the rename s/count/bytes/?  Would it be better to get the name right
> in 1/11?

It made like the bdrv_co_pwritev interface. For the
bdrv_pwrite_compressed() func also need rename s/count/bytes/ in 1/11.

>>   {
>>       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;
>
> This is a (temporary) regression - since none of the drivers have
> .bdrv_co_write_compressed yet, you will always fail.  Rather, the
> transition period should support both interfaces at once...
>
>>       }
>> -    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);
>
> ...and call into either the old or the new interface according to what
> is present.
>
>
>> +int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
>> +                           const void *buf, int count)
>> +{
>> +    BdrvWriteCompressedCo data;
>> +    QEMUIOVector qiov;
>> +    BlockDriver *drv = bs->drv;
>> +    struct iovec iov = {
>> +        .iov_base = (void *)buf,
>> +        .iov_len = count,
>> +    };
>> +    qemu_iovec_init_external(&qiov, &iov, 1);
>>
>> -    return drv->bdrv_write_compressed(bs, offset >> BDRV_SECTOR_BITS, buf,
>> -                                      count >> BDRV_SECTOR_BITS);
>> +    data = (BdrvWriteCompressedCo) {
>> +        .bs     = bs,
>> +        .offset = offset,
>> +        .qiov   = &qiov,
>> +        .ret    = -EINPROGRESS,
>> +    };
>> +
>> +    if (!drv) {
>> +        return -ENOMEDIUM;
>> +    }
>> +
>> +    if (drv->bdrv_write_compressed) {
>> +        int ret = bdrv_check_byte_request(bs, offset, count);
>> +        if (ret < 0) {
>> +            return ret;
>> +        }
>> +        assert(QLIST_EMPTY(&bs->dirty_bitmaps));
>> +        return drv->bdrv_write_compressed(bs, offset >> BDRV_SECTOR_BITS, buf,
>> +                                          count >> BDRV_SECTOR_BITS);
>> +    }
>
> Oh, you're catering to the old code up front, without a coroutine, and
> only the new code gets coroutine treatment.  Maybe it's okay after all.

Yes, it is made for a gradual transition from
drv->bdrv_write_compressed to drv->bdrv_co_write_compressed.

>> +
>> +    if (qemu_in_coroutine()) {
>> +        /* Fast-path if already in coroutine context */
>> +        bdrv_write_compressed_co_entry(&data);
>> +    } else {
>> +        AioContext *aio_context = bdrv_get_aio_context(bs);
>> +
>> +        Coroutine *co = qemu_coroutine_create(bdrv_write_compressed_co_entry);
>> +        qemu_coroutine_enter(co, &data);
>> +        while (data.ret == -EINPROGRESS) {
>> +            aio_poll(aio_context, true);
>> +        }
>> +    }
>> +    return data.ret;
>>   }
>>
>>   int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
>> diff --git a/include/block/block_int.h b/include/block/block_int.h
>> index 30a9717..ccba9c9 100644
>> --- 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,
>
> Might be better to name this bdrv_co_pwrite_compressed if we want to
> make it byte-based...
>
>> +        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
>
> ...it seems odd that you have to add a new sector-based interface given
> that you are trying to convert to byte-based.
>

When I sent this patch, Kevin had not yet converted the sector-based
interfaces to byte-based for format drivers :)

>> +
>>       int (*bdrv_snapshot_create)(BlockDriverState *bs,
>>                                   QEMUSnapshotInfo *sn_info);
>>       int (*bdrv_snapshot_goto)(BlockDriverState *bs,
>> @@ -535,6 +538,8 @@ int coroutine_fn bdrv_co_preadv(BlockDriverState *bs,
>>   int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
>>       int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
>>       BdrvRequestFlags flags);
>> +int coroutine_fn bdrv_co_pwritev_compressed(BlockDriverState *bs,
>> +    int64_t offset, unsigned int bytes, QEMUIOVector *qiov);
>>
>>   int get_tmp_filename(char *filename, int size);
>>   BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
>> diff --git a/qemu-img.c b/qemu-img.c
>> index eb744d4..ab54027 100644
>> --- a/qemu-img.c
>> +++ b/qemu-img.c
>> @@ -2024,7 +2024,7 @@ static int img_convert(int argc, char **argv)
>>           const char *preallocation =
>>               qemu_opt_get(opts, BLOCK_OPT_PREALLOC);
>>
>> -        if (!drv->bdrv_write_compressed) {
>> +        if (!drv->bdrv_write_compressed && !drv->bdrv_co_write_compressed) {
>>               error_report("Compression not supported for this file format");
>>               ret = -1;
>>               goto out;
>>
>