[PATCH] nvmet: report backend transport errors as path errors

[Gleb Chesnokov <gleb.chesnokov@scst.dev>]

The block backend maps BLK_STS_TRANSPORT to NVME_SC_INTERNAL with DNR
set. This discards the backend's transport error classification. A Linux
native multipath host completes the request before considering path
failover, even if another controller can still access the namespace.

Map BLK_STS_TRANSPORT to NVME_SC_INTERNAL_PATH_ERROR without DNR instead.
The transport failure is behind the controller, so report an internal
path error rather than a host path error. Associate the error log entry
with the namespace, as for the existing access-denied status.

This allows otherwise retryable native multipath requests to reach path
error handling.

Signed-off-by: Gleb Chesnokov <gleb.chesnokov@scst.dev>
---
OpenAI Codex assisted with the code analysis, patch and changelog.

 drivers/nvme/target/io-cmd-bdev.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index 72618dced191..da640b8e8241 100644
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -167,6 +167,10 @@ u16 blk_to_nvme_status(struct nvmet_req *req, blk_status_t blk_sts)
 		status = NVME_SC_ACCESS_DENIED;
 		req->error_loc = offsetof(struct nvme_rw_command, nsid);
 		break;
+	case BLK_STS_TRANSPORT:
+		status = NVME_SC_INTERNAL_PATH_ERROR;
+		req->error_loc = offsetof(struct nvme_rw_command, nsid);
+		break;
 	case BLK_STS_IOERR:
 	default:
 		status = NVME_SC_INTERNAL | NVME_STATUS_DNR;

base-commit: 7e1392a42ea288d70a266f6553fe06f57f8647ea
-- 
2.56.0