[PATCH v5] nvmet: report ns's vwc not present

[Guixin Liu <kanie@linux.alibaba.com>]

Currently, we report that controller has vwc even though the ns may
not have vwc. Report ns's vwc not present when not buffered_io or
backdev doesn't have vwc.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
Based on Keith's v4 patch,
Changes from v4 to v5:
- When the backend is file, report support vwc even though buffered_io is
  disable, and add an annotation to expain it.

 drivers/nvme/target/admin-cmd.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/nvme/target/admin-cmd.c b/drivers/nvme/target/admin-cmd.c
index 0a9fdc533186..934b401fbc2f 100644
--- a/drivers/nvme/target/admin-cmd.c
+++ b/drivers/nvme/target/admin-cmd.c
@@ -934,6 +934,13 @@ static void nvmet_execute_id_cs_indep(struct nvmet_req *req)
 		id->nsattr |= NVME_NS_ATTR_RO;
 	if (req->ns->bdev && !bdev_nonrot(req->ns->bdev))
 		id->nsfeat |= NVME_NS_ROTATIONAL;
+	/*
+	 * We need flush command to flush the file's metadata,
+	 * so report supporting vwc if backend is file, even
+	 * though buffered_io is disable.
+	 */
+	if (req->ns->bdev && !bdev_write_cache(req->ns->bdev))
+		id->nsfeat |= NVME_NS_VWC_NOT_PRESENT;
 
 	status = nvmet_copy_to_sgl(req, 0, id, sizeof(*id));
 	kfree(id);
-- 
2.43.0