Re: [PATCH] hw/nvme: Add support for setting the MQES for the NVMe emulation

[Keith Busch]

On Thu, Apr 04, 2024 at 01:04:18PM +0100, John Berg wrote:
> The MQES field in the CAP register describes the Maximum Queue Entries
> Supported for the IO queues of an NVMe controller. Adding a +1 to the
> value in this field results in the total queue size. A full queue is
> when a queue of size N contains N - 1 entries, and the minimum queue
> size is 2. Thus the lowest MQES value is 1.
> 
> This patch adds the new mqes property to the NVMe emulation which allows
> a user to specify the maximum queue size by setting this property. This
> is useful as it enables testing of NVMe controller where the MQES is
> relatively small. The smallest NVMe queue size supported in NVMe is 2
> submission and completion entries, which means that the smallest legal
> mqes value is 1.
> 
> The following example shows how the mqes can be set for a the NVMe
> emulation:
> 
> -drive id=nvme0,if=none,file=nvme.img,format=raw
> -device nvme,drive=nvme0,serial=foo,mqes=1
> 
> If the mqes property is not provided then the default mqes will still be
> 0x7ff (the queue size is 2048 entries).

Looks good. I had to double check where nvme_create_sq() was getting its
limit from when processing the host command, and sure enough it's
directly from the register field.

Reviewed-by: Keith Busch <kbusch@kernel.org>