nvme: implement the Flush command

Implement a real flush instead of faking it.  This is especially important
as Qemu assume Write back cashing by default and thus requires a working
cache flush operation for data integrity.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 17 insertions, 3 deletions

diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index c6a6a0e49a..dc9caf07fe 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -207,11 +207,23 @@ static void nvme_rw_cb(void *opaque, int ret)
     } else {
         req->status = NVME_INTERNAL_DEV_ERROR;
     }
-
-    qemu_sglist_destroy(&req->qsg);
+    if (req->has_sg) {
+        qemu_sglist_destroy(&req->qsg);
+    }
     nvme_enqueue_req_completion(cq, req);
 }
 
+static uint16_t nvme_flush(NvmeCtrl *n, NvmeNamespace *ns, NvmeCmd *cmd,
+    NvmeRequest *req)
+{
+    req->has_sg = false;
+    block_acct_start(blk_get_stats(n->conf.blk), &req->acct, 0,
+         BLOCK_ACCT_FLUSH);
+    req->aiocb = blk_aio_flush(n->conf.blk, nvme_rw_cb, req);
+
+    return NVME_NO_COMPLETE;
+}
+
 static uint16_t nvme_rw(NvmeCtrl *n, NvmeNamespace *ns, NvmeCmd *cmd,
     NvmeRequest *req)
 {
@@ -235,6 +247,7 @@ static uint16_t nvme_rw(NvmeCtrl *n, NvmeNamespace *ns, NvmeCmd *cmd,
     }
     assert((nlb << data_shift) == req->qsg.size);
 
+    req->has_sg = true;
     dma_acct_start(n->conf.blk, &req->acct, &req->qsg,
                    is_write ? BLOCK_ACCT_WRITE : BLOCK_ACCT_READ);
     req->aiocb = is_write ?
@@ -256,7 +269,7 @@ static uint16_t nvme_io_cmd(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
     ns = &n->namespaces[nsid - 1];
     switch (cmd->opcode) {
     case NVME_CMD_FLUSH:
-        return NVME_SUCCESS;
+        return nvme_flush(n, ns, cmd, req);
     case NVME_CMD_WRITE:
     case NVME_CMD_READ:
         return nvme_rw(n, ns, cmd, req);
diff --git a/hw/block/nvme.h b/hw/block/nvme.h
index b6ccb655a6..bf3a3ccac8 100644
--- a/hw/block/nvme.h
+++ b/hw/block/nvme.h
@@ -638,6 +638,7 @@ typedef struct NvmeRequest {
     struct NvmeSQueue       *sq;
     BlockAIOCB              *aiocb;
     uint16_t                status;
+    bool                    has_sg;
     NvmeCqe                 cqe;
     BlockAcctCookie         acct;
     QEMUSGList              qsg;