The SPC-6 specification says that the PREEMPT service action ignores the
TYPE field when there is no reservation. However, the LIO Linux iSCSI
target rejects commands with a zero TYPE field. The field never ends up
being used in this case, so replace it with a "valid" value to work
around the issue.

Reported-by: Qing Wang <qinwang@redhat.com>
Buglink: https://redhat.atlassian.net/browse/RHEL-155807
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/scsi/constants.h | 10 ++++++++++
 hw/scsi/scsi-generic.c   | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/scsi/constants.h b/include/scsi/constants.h
index cb97bdb636..717e470a5d 100644
--- a/include/scsi/constants.h
+++ b/include/scsi/constants.h
@@ -340,4 +340,14 @@
 #define PRO_REGISTER_AND_MOVE                   0x07
 #define PRO_REPLACE_LOST_RESERVATION            0x08
 
+/*
+ * Persistent reservation types
+ */
+#define PR_TYPE_WRITE_EXCLUSIVE             0x1
+#define PR_TYPE_EXCLUSIVE_ACCESS            0x3
+#define PR_TYPE_WRITE_EXCLUSIVE_REG_ONLY    0x5
+#define PR_TYPE_EXCLUSIVE_ACCESS_REG_ONLY   0x6
+#define PR_TYPE_WRITE_EXCLUSIVE_ALL_REGS    0x7
+#define PR_TYPE_EXCLUSIVE_ACCESS_ALL_REGS   0x8
+
 #endif
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index b55d068323..349dea6bdd 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -453,6 +453,16 @@ static bool scsi_generic_pr_preempt(SCSIDevice *s, uint64_t key,
     uint64_t key_be = cpu_to_be64(key);
     int ret;
 
+    /*
+     * The LIO iSCSI target in Linux up to at least version 7.0 rejects PREEMPT
+     * commands with a zero TYPE field although the SPC-6 specification says
+     * the field should be ignored when there is no persistent reservation.
+     * Work around this by choosing an arbitrary valid PR type value.
+     */
+    if (resv_type == 0) {
+        resv_type = PR_TYPE_WRITE_EXCLUSIVE;
+    }
+
     cmd[0] = PERSISTENT_RESERVE_OUT;
     cmd[1] = PRO_PREEMPT;
     cmd[2] = resv_type & 0xf;
-- 
2.53.0