On Tue, Oct 18, 2011 at 7:00 AM, Marcelo Tosatti <mtosa...@redhat.com> wrote:
> On Mon, Oct 17, 2011 at 04:47:31PM +0100, Stefan Hajnoczi wrote:
>> 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;
>> + 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);
>
> The tracked request should include cluster round info?
When checking A and B for overlap, only one of them needs to be
rounded in order for overlap detection to be correct. Therefore we
can store the original request [start, length) in tracked_requests and
only round the new request.
Stefan
