Re: [RFC PATCH 3/3] hw/block/nvme: add nvme_inject_state HMP command

[Keith Busch]

On Thu, Feb 11, 2021 at 04:52:52AM +0900, Minwoo Im wrote:
> nvme_inject_state command is to give a controller state to be.
> Human Monitor Interface(HMP) supports users to make controller to a
> specified state of:
> 
>       normal:                 Normal state (no injection)
>       cmd-interrupted:        Commands will be interrupted internally
> 
> This patch is just a start to give dynamic command from the HMP to the
> QEMU NVMe device model.  If "cmd-interrupted" state is given, then the
> controller will return all the CQ entries with Command Interrupts status
> code.
> 
> Usage:
>       -device nvme,id=nvme0,....
> 
>       (qemu) nvme_inject_state nvme0 cmd-interrupted
> 
>       <All the commands will be interrupted internally>
> 
>       (qemu) nvme_inject_state nvme0 normal
> 
> This feature is required to test Linux kernel NVMe driver for the
> command retry feature.

Once the user sets the injected state, all commands return that status
until the user injects the normal state, so the CRD time is meaningless
here. If we're really going this route, the state needs to return to
normal on it's own.

But I would prefer to see advanced retry tied to real errors that can be
retried, like if we got an EBUSY or EAGAIN errno or something like that.

The interface you found to implement this is very interesting though.