Re: [Qemu-devel] [PATCH V19 7/8] add-cow file format core code.

[Stefan Hajnoczi]

On Thu, May 30, 2013 at 06:00:24PM +0800, Dongxu Wang wrote:
> +static coroutine_fn int add_cow_co_writev(BlockDriverState *bs,
> +                                          int64_t sector_num,
> +                                          int remaining_sectors,
> +                                          QEMUIOVector *qiov)
> +{
> +    BDRVAddCowState *s = bs->opaque;
> +    int ret = 0, i;
> +    QEMUIOVector hd_qiov;
> +    uint8_t *table;
> +    uint64_t offset;
> +    int mask = s->cluster_sectors - 1;
> +    int cluster_mask = s->cluster_size - 1;
> +    AddCowMeta *meta = NULL;
> +
> +    if (remaining_sectors == 0) {
> +        return ret;
> +    }
> +
> +    qemu_co_mutex_lock(&s->lock);
> +
> +    meta = g_malloc0(sizeof(*meta));
> +again:
> +    *meta = (AddCowMeta) {
> +        .next           = QLIST_FIRST(&s->cluster_allocs),
> +        .start_sector   = sector_num,
> +        .remaining_sectors  = remaining_sectors,
> +    };
> +    if (handle_dependencies(bs, sector_num, remaining_sectors) == -EAGAIN) {
> +        goto again;
> +    }
> +    qemu_co_queue_init(&meta->dependent_requests);
> +    QLIST_INSERT_HEAD(&s->cluster_allocs, meta, next_in_flight);
> +    qemu_iovec_init(&hd_qiov, qiov->niov);

hd_qiov is unused.

> +    ret = bdrv_co_writev(s->image_hd, sector_num, remaining_sectors, qiov);

s->lock is held so write requests block other requests, this is not
parallel.