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block: core copy-on-read logic

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Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2011-11-17 13:40:31 +00:00 committed by Kevin Wolf
parent d83947ac6d
commit ab1859218a
2 changed files with 73 additions and 0 deletions
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72
block.c
View File

@ -1469,6 +1469,61 @@ 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);
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
*/
@ -1496,7 +1551,24 @@ 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;
}

1
trace-events
View File

@ -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"