[Qemu-devel] [PATCH 2/3] virtio-blk: Bypass error action and I/O accounting on invalid r/w

[Markus Armbruster]

When a device model's I/O operation fails, we execute the error
action.  This lets layers above QEMU implement thin provisioning, or
attempt to correct errors before they reach the guest.  But when the
I/O operation fails because its invalid, reporting the error to the
guest is the only sensible action.

If the guest's read or write asks for an invalid sector range, fail
the request right away, without considering the error action.  No
change with error action BDRV_ACTION_REPORT.

Furthermore, bypass I/O accounting, because we want to track only I/O
that actually reaches the block layer.

The next commit will extend "invalid sector range" to cover attempts
to read/write beyond the end of the medium.

Signed-off-by: Markus Armbruster <address@hidden>
---
 hw/block/virtio-blk.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index f2b4dca..2c68d0d 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -300,15 +300,16 @@ static void virtio_blk_handle_write(VirtIOBlockReq *req, 
MultiReqBuffer *mrb)
 
     sector = ldq_p(&req->out->sector);
 
-    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_WRITE);
-
     trace_virtio_blk_handle_write(req, sector, req->qiov.size / 512);
 
     if (!virtio_blk_sect_range_ok(req->dev, sector, req->qiov.size)) {
-        virtio_blk_rw_complete(req, -EIO);
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
+        g_free(req);
         return;
     }
 
+    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_WRITE);
+
     if (mrb->num_writes == 32) {
         virtio_submit_multiwrite(req->dev->bs, mrb);
     }
@@ -330,14 +331,15 @@ static void virtio_blk_handle_read(VirtIOBlockReq *req)
 
     sector = ldq_p(&req->out->sector);
 
-    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_READ);
-
     trace_virtio_blk_handle_read(req, sector, req->qiov.size / 512);
 
     if (!virtio_blk_sect_range_ok(req->dev, sector, req->qiov.size)) {
-        virtio_blk_rw_complete(req, -EIO);
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
+        g_free(req);
         return;
     }
+
+    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_READ);
     bdrv_aio_readv(req->dev->bs, sector, &req->qiov,
                    req->qiov.size / BDRV_SECTOR_SIZE,
                    virtio_blk_rw_complete, req);
-- 
1.9.3