blockdev: reset werror/rerror on drive_del

Paolo Bonzini <pbonzini@redhat.com> suggested the following test case:

1. Launch a guest and wait at the GRUB boot menu:

  qemu-system-x86_64 -enable-kvm -m 1024 \
   -drive if=none,cache=none,file=test.img,id=foo,werror=stop,rerror=stop
   -device virtio-blk-pci,drive=foo,id=virtio0,addr=4

2. Hot unplug the device:

  (qemu) drive_del foo

3. Select the first boot menu entry

Without this patch the guest pauses due to ENOMEDIUM.  The guest is
stuck in a continuous pause loop since the I/O request is retried and
fails immediately again when the guest is resumed.

With this patch the error is reported to the guest.

Note that this scenario actually happens sometimes during libvirt disk
hot unplug, where device_del is followed by drive_del.  I/O may still be
submitted to the drive after drive_del if the guest does not process the
PCI hot unplug notification.

Reported-by: Dafna Ron <dron@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/blockdev.c b/blockdev.c
index b9b2d10e6b..9937311aac 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1180,6 +1180,10 @@ int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
      */
     if (bdrv_get_attached_dev(bs)) {
         bdrv_make_anon(bs);
+
+        /* Further I/O must not pause the guest */
+        bdrv_set_on_error(bs, BLOCKDEV_ON_ERROR_REPORT,
+                          BLOCKDEV_ON_ERROR_REPORT);
     } else {
         drive_uninit(drive_get_by_blockdev(bs));
     }