[PATCH] Allow BLKIF_OP_WRITE_BARRIER or BLKIF_OP_FLUSH_DISKCACHE...

[Owen Smith <owen.smith@xxxxxxxxx>]

... when a SCSIOP_SYNCHRONIZE_CACHE is issued, which should be the last
operation issued by the crash kernel.
Certain backends do not advertise WriteBarrier support, and use SyncDiskCache
instead. Add support for creating crashdumps on these backends.

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxx>
---
 src/xencrsh/frontend.c | 13 ++++++++++++-
 src/xencrsh/frontend.h |  1 +
 src/xencrsh/pdo.c      | 27 ++++++++++++++++++++++++---
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/src/xencrsh/frontend.c b/src/xencrsh/frontend.c
index d88f498..0b9e46b 100644
--- a/src/xencrsh/frontend.c
+++ b/src/xencrsh/frontend.c
@@ -268,6 +268,7 @@ FrontendInsertRequestOnRing(
         }
         break;
     case BLKIF_OP_WRITE_BARRIER:
+    case BLKIF_OP_FLUSH_DISKCACHE:
         RingReq->operation          = Request->Operation;
         RingReq->nr_segments        = 0;
         RingReq->handle             = (USHORT)Frontend->DeviceId;
@@ -470,6 +471,15 @@ __ReadFeatures(
         Frontend->FeatureBarrier = FALSE;
     }
 
+    Status = StoreRead(NULL, Frontend->BackendPath,
+                        "feature-flush-cache", &Buffer);
+    if (NT_SUCCESS(Status)) {
+        Frontend->FeatureFlush = (strtoul(Buffer, NULL, 10) == 1);
+        AustereFree(Buffer);
+    } else {
+        Frontend->FeatureFlush = FALSE;
+    }
+
     Status = StoreRead(NULL, Frontend->BackendPath,
                         "feature-discard", &Buffer);
     if (NT_SUCCESS(Status)) {
@@ -479,9 +489,10 @@ __ReadFeatures(
         Frontend->FeatureDiscard = FALSE;
     }
 
-    LogVerbose("Features: DomId=%d, RingOrder=0, %s %s\n",
+    LogVerbose("Features: DomId=%d, RingOrder=0, %s %s %s\n",
                 Frontend->BackendId,
                 Frontend->FeatureBarrier ? "BARRIER" : "NOT_BARRIER",
+                Frontend->FeatureFlush ? "FLUSH" : "NOT_FLUSH",
                 Frontend->FeatureDiscard ? "DISCARD" : "NOT_DISCARD");
 }
 static VOID
diff --git a/src/xencrsh/frontend.h b/src/xencrsh/frontend.h
index 174e4d7..2e2c305 100644
--- a/src/xencrsh/frontend.h
+++ b/src/xencrsh/frontend.h
@@ -62,6 +62,7 @@ typedef struct _XENVBD_FRONTEND {
     // Capabilities
     BOOLEAN                     Connected;
     BOOLEAN                     FeatureBarrier;
+    BOOLEAN                     FeatureFlush;
     BOOLEAN                     FeatureDiscard;
     BOOLEAN                     Paging;
     BOOLEAN                     Hibernation;
diff --git a/src/xencrsh/pdo.c b/src/xencrsh/pdo.c
index 9fe3c53..76c4d59 100644
--- a/src/xencrsh/pdo.c
+++ b/src/xencrsh/pdo.c
@@ -564,17 +564,31 @@ PrepareSyncCache(
 {
     PXENVBD_SRBEXT          SrbExt = GetSrbExt(Srb);
     PXENVBD_REQUEST         Request;
-    
+    UCHAR                   Operation;
+
+    if (Pdo->Frontend.FeatureBarrier) {
+        Operation = BLKIF_OP_WRITE_BARRIER;
+    } else if (Pdo->Frontend.FeatureFlush) {
+        Operation = BLKIF_OP_FLUSH_DISKCACHE;
+    } else {
+        // cannot submit this to backend, just complete the SRB
+        Srb->SrbStatus = SRB_STATUS_SUCCESS;
+        Srb->ScsiStatus = 0x00; // SCSI_GOOD
+
+        FdoCompleteSrb(Pdo->Fdo, Srb);
+        return;
+    }
+
     SrbExt->NumRequests = 1;
     Request = &SrbExt->Requests[0];
     Request->Srb = Srb;
 
-    Request->Operation      = BLKIF_OP_WRITE_BARRIER;
+    Request->Operation      = Operation;
     Request->NrSegments     = 0;
     Request->FirstSector    = Cdb_LogicalBlock(Srb);
     Request->NrSectors      = 0;
 
-    __UpdateStats(Pdo, BLKIF_OP_WRITE_BARRIER);
+    __UpdateStats(Pdo, Operation);
     QueueInsertTail(&Pdo->PreparedSrbs, Srb);
 }
 
@@ -692,6 +706,13 @@ PdoCompleteSubmittedRequest(
             Pdo->Frontend.FeatureBarrier = FALSE;
         }
         break;
+    case BLKIF_OP_FLUSH_DISKCACHE:
+        LogVerbose("FLUSH\n");
+        if (Status == BLKIF_RSP_EOPNOTSUPP) {
+            // remove supported feature
+            Pdo->Frontend.FeatureFlush = FALSE;
+        }
+        break;
     case BLKIF_OP_DISCARD:
         LogVerbose("DISCARD\n");
         if (Status == BLKIF_RSP_EOPNOTSUPP) {
-- 
2.46.0.windows.1