nvme-fabrics: handle zero MAXCMD without closing the connection

jira LE-3460
Rebuild_History Non-Buildable kernel-6.12.0-55.18.1.el10_0
commit-author Maurizio Lombardi <[email protected]>
commit 88c23a3

The NVMe specification states that MAXCMD is mandatory
for NVMe-over-Fabrics implementations. However, some NVMe/TCP
and NVMe/FC arrays from major vendors have buggy firmware
that reports MAXCMD as zero in the Identify Controller data structure.

Currently, the implementation closes the connection in such cases,
completely preventing the host from connecting to the target.

Fix the issue by printing a clear error message about the firmware bug
and allowing the connection to proceed. It assumes that the
target supports a MAXCMD value of SQSIZE + 1. If any issues arise,
the user can manually adjust SQSIZE to mitigate them.

Fixes: 4999568 ("nvme-fabrics: check max outstanding commands")
	Signed-off-by: Maurizio Lombardi <[email protected]>
	Reviewed-by: Laurence Oberman <[email protected]>
	Reviewed-by: Christoph Hellwig <[email protected]>
	Signed-off-by: Keith Busch <[email protected]>
(cherry picked from commit 88c23a3)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

drivers/nvme/host/core.c

@@ -3250,8 +3250,9 @@ static int nvme_check_ctrl_fabric_info(struct nvme_ctrl *ctrl, struct nvme_id_ct
 	}
 
 	if (!ctrl->maxcmd) {
-		dev_err(ctrl->device, "Maximum outstanding commands is 0\n");
-		return -EINVAL;
+		dev_warn(ctrl->device,
+			"Firmware bug: maximum outstanding commands is 0\n");
+		ctrl->maxcmd = ctrl->sqsize + 1;
 	}
 
 	return 0;