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Re: [Qemu-devel] [RFC 5/6] block: core copy-on-read logic
From: |
Marcelo Tosatti |
Subject: |
Re: [Qemu-devel] [RFC 5/6] block: core copy-on-read logic |
Date: |
Tue, 18 Oct 2011 12:03:51 -0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Oct 17, 2011 at 04:47:31PM +0100, Stefan Hajnoczi wrote:
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> 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;
> + 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);
> + if (ret < 0) {
> + goto out;
> + }
This lacks shared base image support, BTW (as in copy should be
performed only if cluster not in destination chain). Could be added
later.
- [Qemu-devel] [RFC 0/6] block: generic copy-on-read, Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 5/6] block: core copy-on-read logic, Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 3/6] block: wait for overlapping requests, Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 1/6] block: add request tracking, Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 2/6] block: add bdrv_set_copy_on_read(), Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 6/6] block: add -drive copy-on-read=on|off, Stefan Hajnoczi, 2011/10/17
- [Qemu-devel] [RFC 4/6] block: request overlap detection, Stefan Hajnoczi, 2011/10/17