Re: [PATCH v2 1/6] qcow2: Allow writing compressed data to multiple clusters

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

02.10.2019 17:22, Andrey Shinkevich wrote:
> QEMU currently supports writing compressed data of size less than or
> equal to one cluster. This patch allows writing QCOW2 compressed data
> that exceed one cluster. The implementation is simple, we split buffered
> data into separate clusters and write them using the existing
> functionality. For unaligned requests, we use a workaround that writes
> the data without compression.
> 
> Suggested-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>   block/qcow2.c | 113 +++++++++++++++++++++++++++++++++++++++++++---------------
>   1 file changed, 85 insertions(+), 28 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 7961c05..54ccaf6 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -4152,10 +4152,8 @@ fail:
>       return ret;
>   }
>   
> -/* XXX: put compressed sectors first, then all the cluster aligned
> -   tables to avoid losing bytes in alignment */
>   static coroutine_fn int
> -qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
> +qcow2_co_pwritev_compressed_task(BlockDriverState *bs,
>                                    uint64_t offset, uint64_t bytes,
>                                    QEMUIOVector *qiov, size_t qiov_offset)
>   {
> @@ -4165,36 +4163,14 @@ qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
>       uint8_t *buf, *out_buf;
>       uint64_t cluster_offset;
>   
> -    if (has_data_file(bs)) {
> -        return -ENOTSUP;
> -    }
> -
> -    if (bytes == 0) {
> -        /* align end of file to a sector boundary to ease reading with
> -           sector based I/Os */
> -        int64_t len = bdrv_getlength(bs->file->bs);
> -        if (len < 0) {
> -            return len;
> -        }
> -        return bdrv_co_truncate(bs->file, len, PREALLOC_MODE_OFF, NULL);
> -    }
> -
> -    if (offset_into_cluster(s, offset)) {
> -        return -EINVAL;
> -    }
> +    assert(bytes <= s->cluster_size);

I think we'd better assert

assert(bytes == s->cluster_size || (bytes < s->cluster_size && (offset + bytes == bdrv_getlength())

to match old logic.jkjkj


>   
>       buf = qemu_blockalign(bs, s->cluster_size);
> -    if (bytes != s->cluster_size) {
> -        if (bytes > s->cluster_size ||
> -            offset + bytes != bs->total_sectors << BDRV_SECTOR_BITS)
> -        {
> -            qemu_vfree(buf);
> -            return -EINVAL;
> -        }
> +    if (bytes < s->cluster_size) {
>           /* Zero-pad last write if image size is not cluster aligned */
>           memset(buf + bytes, 0, s->cluster_size - bytes);
>       }
> -    qemu_iovec_to_buf(qiov, qiov_offset, buf, bytes);
> +    qemu_iovec_to_buf(qiov, qiov_offset, buf, s->cluster_size);

Why did you changed it to s->cluster_size? bytes may be less than cluster

>   
>       out_buf = g_malloc(s->cluster_size);
>   
> @@ -4228,6 +4204,9 @@ qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
>   
>       BLKDBG_EVENT(s->data_file, BLKDBG_WRITE_COMPRESSED);
>       ret = bdrv_co_pwrite(s->data_file, cluster_offset, out_len, out_buf, 0);
> +    if (ret == -ENOTSUP) {
> +        ret = qcow2_co_pwritev_part(bs, offset, bytes, qiov, qiov_offset, 0);
> +    }

It should not be here:
1. write will unlikely return ENOTSUP
2. if you mean fallback to normal write if we failed to compress, it's done above already.


>       if (ret < 0) {
>           goto fail;
>       }
> @@ -4239,6 +4218,84 @@ fail:
>       return ret;
>   }
>   
> +static coroutine_fn int qcow2_co_pwritev_compressed_task_entry(AioTask *task)
> +{
> +    Qcow2AioTask *t = container_of(task, Qcow2AioTask, task);
> +
> +    assert(!t->cluster_type);

and assert(!t->l2meta)

> +
> +    return qcow2_co_pwritev_compressed_task(t->bs, t->offset, t->bytes, t->qiov,
> +                                            t->qiov_offset);
> +}
> +
> +/*
> + * XXX: put compressed sectors first, then all the cluster aligned
> +   tables to avoid losing bytes in alignment
> + */
> +static coroutine_fn int
> +qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
> +                                 uint64_t offset, uint64_t bytes,
> +                                 QEMUIOVector *qiov, size_t qiov_offset)
> +{
> +    BDRVQcow2State *s = bs->opaque;
> +    QCowL2Meta *l2meta = NULL;

it's always NULL and actually unused.

> +    AioTaskPool *aio = NULL;
> +    uint64_t curr_off = 0;
> +    int ret;
> +
> +    if (has_data_file(bs)) {
> +        return -ENOTSUP;
> +    }
> +
> +    if (bytes == 0) {
> +        /*
> +         * align end of file to a sector boundary to ease reading with
> +         * sector based I/Os
> +         */
> +        int64_t cluster_offset = bdrv_getlength(bs->file->bs);

Hmm, I like old variable name 'len' more.

> +        if (cluster_offset < 0) {
> +            return cluster_offset;
> +        }
> +        return bdrv_co_truncate(bs->file, cluster_offset, PREALLOC_MODE_OFF,
> +                                NULL);
> +    }
> +
> +    if (offset_into_cluster(s, offset)) {
> +        return -EINVAL;
> +    }
> +
> +    while (bytes && aio_task_pool_status(aio) == 0) {
> +        uint32_t chunk_size = MIN(bytes, s->cluster_size);
> +
> +        assert((curr_off & (BDRV_SECTOR_SIZE - 1)) == 0);
> +        assert((chunk_size & (BDRV_SECTOR_SIZE - 1)) == 0);

first: always use QEMU_IS_ALIGNED instead
second: why do you add these asserts, do we need them?

> +
> +        if (!aio && chunk_size != bytes) {
> +            aio = aio_task_pool_new(QCOW2_MAX_WORKERS);
> +        }
> +
> +        ret = qcow2_add_task(bs, aio, qcow2_co_pwritev_compressed_task_entry,
> +                             0, 0, offset + curr_off, chunk_size,
> +                             qiov, qiov_offset, l2meta);
> +        if (ret < 0) {
> +            break;
> +        }
> +        qiov_offset += chunk_size;
> +        curr_off += chunk_size;

you may just offset += chunk_size and drop extra variable

> +        bytes -= chunk_size;
> +    }
> +
> +    if (aio) {
> +        aio_task_pool_wait_all(aio);
> +        if (ret == 0) {
> +            ret = aio_task_pool_status(aio);
> +        }
> +        g_free(aio);
> +    }
> +
> +    return ret;
> +}
> +
>   static int coroutine_fn
>   qcow2_co_preadv_compressed(BlockDriverState *bs,
>                              uint64_t file_cluster_offset,
> 

overall - OK

-- 
Best regards,
Vladimir