nvme: properly report volatile write caches

Implement support in Identify and Get/Set Features to properly report
and allow to change the Volatile Write Cache status reported by the
virtual NVMe device.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NKeith Busch <keith.busch@intel.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

hw/block/nvme.c

@@ -487,26 +487,32 @@ static uint16_t nvme_identify(NvmeCtrl *n, NvmeCmd *cmd)
 static uint16_t nvme_get_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
 {
     uint32_t dw10 = le32_to_cpu(cmd->cdw10);
+    uint32_t result;
 
     switch (dw10) {
-    case NVME_NUMBER_OF_QUEUES:
-        req->cqe.result =
-            cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
-        break;
     case NVME_VOLATILE_WRITE_CACHE:
-        req->cqe.result = cpu_to_le32(1);
+        result = blk_enable_write_cache(n->conf.blk);
+        break;
+    case NVME_NUMBER_OF_QUEUES:
+        result = cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
         break;
     default:
         return NVME_INVALID_FIELD | NVME_DNR;
     }
+
+    req->cqe.result = result;
     return NVME_SUCCESS;
 }
 
 static uint16_t nvme_set_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
 {
     uint32_t dw10 = le32_to_cpu(cmd->cdw10);
+    uint32_t dw11 = le32_to_cpu(cmd->cdw11);
 
     switch (dw10) {
+    case NVME_VOLATILE_WRITE_CACHE:
+        blk_set_enable_write_cache(n->conf.blk, dw11 & 1);
+        break;
     case NVME_NUMBER_OF_QUEUES:
         req->cqe.result =
             cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
@@ -831,6 +837,9 @@ static int nvme_init(PCIDevice *pci_dev)
     id->psd[0].mp = cpu_to_le16(0x9c4);
     id->psd[0].enlat = cpu_to_le32(0x10);
     id->psd[0].exlat = cpu_to_le32(0x4);
+    if (blk_enable_write_cache(n->conf.blk)) {
+        id->vwc = 1;
+    }
 
     n->bar.cap = 0;
     NVME_CAP_SET_MQES(n->bar.cap, 0x7ff);