[PATCH 4/4] scsi-disk: Always report RESERVATION_CONFLICT to guest

[Kevin Wolf <kwolf@redhat.com>]

RESERVATION_CONFLICT is not a backend error, but indicates that the
guest tried to make a request that it isn't allowed to execute. Pass the
error to the guest so that it can decide what to do with it.

Without this, if we stop the VM in response to a RESERVATION_CONFLICT,
it can happen that the VM cannot be resumed any more because every
attempt to resume it immediately runs into the same error and stops the
VM again.

One case that expects RESERVATION_CONFLICT errors to be visible in the
guest is running the validation tests in Windows 2019's Failover Cluster
Manager, which intentionally tries to execute invalid requests to see if
they are properly rejected.

Buglink: https://issues.redhat.com/browse/RHEL-50000
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/scsi/scsi-disk.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 69a195177e..e173b238de 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -235,11 +235,17 @@ static bool scsi_handle_rw_error(SCSIDiskReq *r, int ret, bool acct_failed)
     } else {
         /* A passthrough command has completed with nonzero status.  */
         status = ret;
-        if (status == CHECK_CONDITION) {
+        switch (status) {
+        case CHECK_CONDITION:
             req_has_sense = true;
             error = scsi_sense_buf_to_errno(r->req.sense, sizeof(r->req.sense));
-        } else {
+            break;
+        case RESERVATION_CONFLICT:
+            /* Don't apply the error policy, always report to the guest */
+            break;
+        default:
             error = EINVAL;
+            break;
         }
     }
 
@@ -249,8 +255,9 @@ static bool scsi_handle_rw_error(SCSIDiskReq *r, int ret, bool acct_failed)
      * are usually retried immediately, so do not post them to QMP and
      * do not account them as failed I/O.
      */
-    if (req_has_sense &&
-        scsi_sense_buf_is_guest_recoverable(r->req.sense, sizeof(r->req.sense))) {
+    if (!error || (req_has_sense &&
+                   scsi_sense_buf_is_guest_recoverable(r->req.sense,
+                                                       sizeof(r->req.sense)))) {
         action = BLOCK_ERROR_ACTION_REPORT;
         acct_failed = false;
     } else {
-- 
2.45.2