On Thu, Nov 17, 2011 at 9:40 PM, Stefan Hajnoczi
<stefa...@linux.vnet.ibm.com> wrote:
> Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
> ---
> block.c | 72
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> trace-events | 1 +
> 2 files changed, 73 insertions(+), 0 deletions(-)
>
> diff --git a/block.c b/block.c
> index 0eef122..d5faa6c 100644
> --- a/block.c
> +++ b/block.c
> @@ -1464,6 +1464,61 @@ 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)
> +{
> + /* Perform I/O through a temporary buffer so that users who scribble over
> + * their read buffer while the operation is in progress do not end up
> + * modifying the image file. This is critical for zero-copy guest I/O
> + * where anything might happen inside guest memory.
> + */
> + void *bounce_buffer;
> +
> + 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);
Why need to round down/up sector_num/nb_sectors in this function? The
detection of race condition for write request has been done before
this function.
> +
> + 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
> */
> @@ -1491,7 +1546,24 @@ static int coroutine_fn
> bdrv_co_do_readv(BlockDriverState *bs,
> }
>
> tracked_request_begin(&req, bs, sector_num, nb_sectors, false);
> +
> + if (bs->copy_on_read) {
> + int pnum;
> +
> + ret = bdrv_co_is_allocated(bs, sector_num, nb_sectors, &pnum);
> + if (ret < 0) {
> + goto out;
> + }
> +
> + if (!ret || pnum != nb_sectors) {
> + ret = bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, qiov);
> + goto out;
> + }
> + }
> +
> ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
> +
> +out:
> tracked_request_end(&req);
> return ret;
> }
> diff --git a/trace-events b/trace-events
> index 962caca..518b76b 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -69,6 +69,7 @@ bdrv_lock_medium(void *bs, bool locked) "bs %p locked %d"
> bdrv_co_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num
> %"PRId64" nb_sectors %d"
> bdrv_co_writev(void *bs, int64_t sector_num, int nb_sector) "bs %p
> sector_num %"PRId64" nb_sectors %d"
> bdrv_co_io_em(void *bs, int64_t sector_num, int nb_sectors, int is_write,
> void *acb) "bs %p sector_num %"PRId64" nb_sectors %d is_write %d acb %p"
> +bdrv_co_copy_on_readv(void *bs, int64_t sector_num, int nb_sectors, int64_t
> cluster_sector_num, int cluster_nb_sectors) "bs %p sector_num %"PRId64"
> nb_sectors %d cluster_sector_num %"PRId64" cluster_nb_sectors %d"
>
> # hw/virtio-blk.c
> virtio_blk_req_complete(void *req, int status) "req %p status %d"
> --
> 1.7.7.1
>
>
>
--
Regards,
Zhi Yong Wu
