Am 17.10.2011 17:47, schrieb Stefan Hajnoczi:
> Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
> ---
> block.c | 69
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> trace-events | 1 +
> 2 files changed, 70 insertions(+), 0 deletions(-)
>
> diff --git a/block.c b/block.c
> index 0c22741..2aec6b4 100644
> --- a/block.c
> +++ b/block.c
> @@ -1409,6 +1409,55 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t
> offset,
> return 0;
> }
>
> +static int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
> + int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
> +{
> + void *bounce_buffer;
I think the bounce buffer deserves a comment. It may not be obvious for
everyone why it's needed.
> + struct iovec iov;
> + QEMUIOVector bounce_qiov;
> + int64_t cluster_sector_num;
> + int cluster_nb_sectors;
> + size_t skip_bytes;
> + int ret;
> +
> + /* Cover entire cluster so no additional backing file I/O is required
> when
> + * allocating cluster in the image file.
> + */
> + round_to_clusters(bs, sector_num, nb_sectors,
> + &cluster_sector_num, &cluster_nb_sectors);
> +
> + trace_bdrv_co_copy_on_readv(bs, sector_num, nb_sectors,
> + cluster_sector_num, cluster_nb_sectors);
> +
> + iov.iov_len = cluster_nb_sectors * BDRV_SECTOR_SIZE;
> + iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len);
> + qemu_iovec_init_external(&bounce_qiov, &iov, 1);
> +
> + ret = bs->drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors,
> + &bounce_qiov);
> + if (ret < 0) {
> + goto err;
> + }
> +
> + ret = bs->drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors,
> + &bounce_qiov);
> + if (ret < 0) {
> + /* It might be okay to ignore write errors for guest requests. If
> this
> + * is a deliberate copy-on-read then we don't want to ignore the
> error.
> + * Simply report it in all cases.
> + */
> + goto err;
> + }
> +
> + skip_bytes = (sector_num - cluster_sector_num) * BDRV_SECTOR_SIZE;
> + qemu_iovec_from_buffer(qiov, bounce_buffer + skip_bytes,
> + nb_sectors * BDRV_SECTOR_SIZE);
> +
> +err:
> + qemu_vfree(bounce_buffer);
> + return ret;
> +}
> +
> /*
> * Handle a read request in coroutine context
> */
> @@ -1431,7 +1480,27 @@ static int coroutine_fn
> bdrv_co_do_readv(BlockDriverState *bs,
> }
>
> req = tracked_request_add(bs, sector_num, nb_sectors, false);
> +
> + if (bs->copy_on_read) {
> + int pnum;
> +
> + /* TODO it is not safe to call bdrv_is_allocated() in coroutine
> context
> + * because it's a synchronous interface. We probably want a
> + * bdrv_co_is_allocated(). */
> + ret = bdrv_is_allocated(bs, sector_num, nb_sectors, &pnum);
I think I already said it in a reply to another patch, but for the
record: We need bdrv_co_is_allocated() before this can be merged.
Kevin
