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 c30c8f2..a598a19 100644
--- a/block.c
+++ b/block.c
@@ -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;
}
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
