[PATCH V2] nvme-fabrics: handle zero MAXCMD without closing the connection

[PATCH V2] nvme-fabrics: handle zero MAXCMD without closing the connection

[Maurizio Lombardi]

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 host implementation returns an error in such cases,
completely preventing the host from connecting to the target.

Fix the issue by printing a clear warning 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: 4999568184e5 ("nvme-fabrics: check max outstanding commands")
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---

V2: replace dev_err() with dev_warn()

 drivers/nvme/host/core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 52b01a15aad1..30327e3b2662 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3260,8 +3260,9 @@ 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;
-- 
2.43.5

Re: [PATCH V2] nvme-fabrics: handle zero MAXCMD without closing the connection

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH V2] nvme-fabrics: handle zero MAXCMD without closing the connection

[Keith Busch]

On Tue, Dec 03, 2024 at 01:57:32PM +0100, Maurizio Lombardi wrote:
> 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 host implementation returns an error in such cases,
> completely preventing the host from connecting to the target.
> 
> Fix the issue by printing a clear warning 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.

Thanks, applied to nvme-6.13.