block/nvme: Use union of NvmeIdCtrl / NvmeIdNs structures

We allocate an unique chunk of memory then use it for two
different structures. By using an union, we make it clear
the data is overlapping (and we can remove the casts).

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200821195359.1285345-9-philmd@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/nvme.c b/block/nvme.c
index 0992f2fb57955ec4124c4b0e3137c3864b6741b6..b0d55ecfb2599f3b8c26fa5e69eef7ec965d374f 100644 (file)
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -508,9 +508,10 @@ static int nvme_cmd_sync(BlockDriverState *bs, NVMeQueuePair *q,
 static void nvme_identify(BlockDriverState *bs, int namespace, Error **errp)
 {
     BDRVNVMeState *s = bs->opaque;
-    NvmeIdCtrl *idctrl;
-    NvmeIdNs *idns;
-    uint8_t *id;
+    union {
+        NvmeIdCtrl ctrl;
+        NvmeIdNs ns;
+    } *id;
     NvmeLBAF *lbaf;
     uint16_t oncs;
     int r;
@@ -520,14 +521,12 @@ static void nvme_identify(BlockDriverState *bs, int namespace, Error **errp)
         .cdw10 = cpu_to_le32(0x1),
     };
 
-    id = qemu_try_blockalign0(bs, sizeof(NvmeIdCtrl));
+    id = qemu_try_blockalign0(bs, sizeof(*id));
     if (!id) {
         error_setg(errp, "Cannot allocate buffer for identify response");
         goto out;
     }
-    idctrl = (NvmeIdCtrl *)id;
-    idns = (NvmeIdNs *)id;
-    r = qemu_vfio_dma_map(s->vfio, id, sizeof(NvmeIdCtrl), true, &iova);
+    r = qemu_vfio_dma_map(s->vfio, id, sizeof(*id), true, &iova);
     if (r) {
         error_setg(errp, "Cannot map buffer for DMA");
         goto out;
@@ -539,22 +538,22 @@ static void nvme_identify(BlockDriverState *bs, int namespace, Error **errp)
         goto out;
     }
 
-    if (le32_to_cpu(idctrl->nn) < namespace) {
+    if (le32_to_cpu(id->ctrl.nn) < namespace) {
         error_setg(errp, "Invalid namespace");
         goto out;
     }
-    s->write_cache_supported = le32_to_cpu(idctrl->vwc) & 0x1;
-    s->max_transfer = (idctrl->mdts ? 1 << idctrl->mdts : 0) * s->page_size;
+    s->write_cache_supported = le32_to_cpu(id->ctrl.vwc) & 0x1;
+    s->max_transfer = (id->ctrl.mdts ? 1 << id->ctrl.mdts : 0) * s->page_size;
     /* For now the page list buffer per command is one page, to hold at most
      * s->page_size / sizeof(uint64_t) entries. */
     s->max_transfer = MIN_NON_ZERO(s->max_transfer,
                           s->page_size / sizeof(uint64_t) * s->page_size);
 
-    oncs = le16_to_cpu(idctrl->oncs);
+    oncs = le16_to_cpu(id->ctrl.oncs);
     s->supports_write_zeroes = !!(oncs & NVME_ONCS_WRITE_ZEROES);
     s->supports_discard = !!(oncs & NVME_ONCS_DSM);
 
-    memset(id, 0, 4096);
+    memset(id, 0, sizeof(*id));
     cmd.cdw10 = 0;
     cmd.nsid = cpu_to_le32(namespace);
     if (nvme_cmd_sync(bs, s->queues[INDEX_ADMIN], &cmd)) {
@@ -562,11 +561,11 @@ static void nvme_identify(BlockDriverState *bs, int namespace, Error **errp)
         goto out;
     }
 
-    s->nsze = le64_to_cpu(idns->nsze);
-    lbaf = &idns->lbaf[NVME_ID_NS_FLBAS_INDEX(idns->flbas)];
+    s->nsze = le64_to_cpu(id->ns.nsze);
+    lbaf = &id->ns.lbaf[NVME_ID_NS_FLBAS_INDEX(id->ns.flbas)];
 
-    if (NVME_ID_NS_DLFEAT_WRITE_ZEROES(idns->dlfeat) &&
-            NVME_ID_NS_DLFEAT_READ_BEHAVIOR(idns->dlfeat) ==
+    if (NVME_ID_NS_DLFEAT_WRITE_ZEROES(id->ns.dlfeat) &&
+            NVME_ID_NS_DLFEAT_READ_BEHAVIOR(id->ns.dlfeat) ==
                     NVME_ID_NS_DLFEAT_READ_BEHAVIOR_ZEROES) {
         bs->supported_write_flags |= BDRV_REQ_MAY_UNMAP;
     }