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From: Pavel Butsykin <pbutsykin@virtuozzo.com>
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Date: Fri, 29 Apr 2016 11:49:04 +0300
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Subject: Re: [Qemu-devel] [PATCH v2 13/17] vmdk: Implement
 .bdrv_co_pwritev() interface
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To: Fam Zheng <famz@redhat.com>, Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, sw@weilnetz.de, stefanha@redhat.com, qemu-block@nongnu.org, mreitz@redhat.com

On 29.04.2016 06:08, Fam Zheng wrote:
> On Thu, 04/28 15:16, Kevin Wolf wrote:
>> +typedef struct VmdkWriteCompressedCo {
>> +    BlockDriverState *bs;
>> +    int64_t sector_num;
>> +    const uint8_t *buf;
>> +    int nb_sectors;
>> +    int ret;
>> +} VmdkWriteCompressedCo;
>> +
>> +static void vmdk_co_write_compressed(void *opaque)
>> +{
>> +    VmdkWriteCompressedCo *co = opaque;
>> +    QEMUIOVector local_qiov;
>> +    uint64_t offset = co->sector_num * BDRV_SECTOR_SIZE;
>> +    uint64_t bytes = co->nb_sectors * BDRV_SECTOR_SIZE;
>> +
>> +    struct iovec iov = (struct iovec) {
>> +        .iov_base   = (uint8_t*) co->buf,
>> +        .iov_len    = bytes,
>> +    };
>> +    qemu_iovec_init_external(&local_qiov, &iov, 1);
>> +
>> +    co->ret = vmdk_pwritev(co->bs, offset, bytes, &local_qiov, false, false);
>
> Should it acquire s->lock?
>
The write_compressed callback is currently used only for image
converting, so I think the lock is not required.

>> +}
>> +
>>   static int vmdk_write_compressed(BlockDriverState *bs,
>>                                    int64_t sector_num,
>>                                    const uint8_t *buf,
>>                                    int nb_sectors)
>>   {
>>       BDRVVmdkState *s = bs->opaque;
>> +
>>       if (s->num_extents == 1 && s->extents[0].compressed) {
>> -        return vmdk_write(bs, sector_num, buf, nb_sectors, false, false);
>> +        Coroutine *co;
>> +        AioContext *aio_context = bdrv_get_aio_context(bs);
>> +        VmdkWriteCompressedCo data = {
>> +            .bs         = bs,
>> +            .sector_num = sector_num,
>> +            .buf        = buf,
>> +            .nb_sectors = nb_sectors,
>> +            .ret        = -EINPROGRESS,
>> +        };
>> +        co = qemu_coroutine_create(vmdk_co_write_compressed);
>> +        qemu_coroutine_enter(co, &data);
>> +        while (data.ret == -EINPROGRESS) {
>> +            aio_poll(aio_context, true);
>> +        }
>> +        return data.ret;
>
> Don't you have a plan to make the creation of coroutine for compressed write in
> in block layer?  Or will bdrv_co_pwritev gain a "compressed" flag
> (BDRV_REQ_COMPRESSED) in the future?
>
Actually, I already have these patches as part of the issue of backup
compression, hope to send today.

> Fam
>
>>       } else {
>>           return -ENOTSUP;
>>       }
>