block/nvme: Implement fake truncate() coroutine

NVMe drive cannot be shrunk.

Since commit c80d8b06cfa we can use the @exact parameter (set
to false) to return success if the block device is larger than
the requested offset (even if we can not be shrunk).

Use this parameter to implement the NVMe truncate() coroutine,
similarly how it is done for the iscsi and file-posix drivers
(see commit 82325ae5f2f "Evaluate @exact in protocol drivers").

Reported-by: Xueqiang Wei <xuwei@redhat.com>
Suggested-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201210125202.858656-1-philmd@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/nvme.c

@@ -1389,6 +1389,29 @@ out:
 
 }
 
+static int coroutine_fn nvme_co_truncate(BlockDriverState *bs, int64_t offset,
+                                         bool exact, PreallocMode prealloc,
+                                         BdrvRequestFlags flags, Error **errp)
+{
+    int64_t cur_length;
+
+    if (prealloc != PREALLOC_MODE_OFF) {
+        error_setg(errp, "Unsupported preallocation mode '%s'",
+                   PreallocMode_str(prealloc));
+        return -ENOTSUP;
+    }
+
+    cur_length = nvme_getlength(bs);
+    if (offset != cur_length && exact) {
+        error_setg(errp, "Cannot resize NVMe devices");
+        return -ENOTSUP;
+    } else if (offset > cur_length) {
+        error_setg(errp, "Cannot grow NVMe devices");
+        return -EINVAL;
+    }
+
+    return 0;
+}
 
 static int nvme_reopen_prepare(BDRVReopenState *reopen_state,
                                BlockReopenQueue *queue, Error **errp)
@@ -1523,6 +1546,7 @@ static BlockDriver bdrv_nvme = {
     .bdrv_close               = nvme_close,
     .bdrv_getlength           = nvme_getlength,
     .bdrv_probe_blocksizes    = nvme_probe_blocksizes,
+    .bdrv_co_truncate         = nvme_co_truncate,
 
     .bdrv_co_preadv           = nvme_co_preadv,
     .bdrv_co_pwritev          = nvme_co_pwritev,