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

From: Klaus Jensen
Subject: Re: [RFC PATCH 3/3] hw/block/nvme: add nvme_inject_state HMP command
Date: Thu, 11 Feb 2021 08:26:25 +0100

On Feb 11 13:24, Keith Busch wrote:
> On Thu, Feb 11, 2021 at 12:38:48PM +0900, Minwoo Im wrote:
> > On 21-02-11 12:00:11, Keith Busch wrote:
> > > 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.
> > 
> > I have seen a thread [1] about ACRE.  Forgive me If I misunderstood this
> > thread or missed something after this thread.  It looks like CRD field in
> > the CQE can be set for any NVMe error state which means it *may* depend on
> > the device status.
> Right! Setting CRD values is at the controller's discretion for any
> error status as long as the host enables ACRE.
> > And this patch just introduced a internal temporarily error state of
> > the controller by returning Command Intrrupted status.
> It's just purely synthetic, though. I was hoping something more natural
> could trigger the status. That might not provide the deterministic
> scenario you're looking for, though.
> I'm not completely against using QEMU as a development/test vehicle for
> corner cases like this, but we are introducing a whole lot of knobs
> recently, and you practically need to be a QEMU developer to even find
> them. We probably should step up the documentation in the wiki along
> with these types of features.

Understood, I'll make docs/specs/nvme.txt and wiki documentation a
priority for 6.0.

> > I think, in this stage, we can go with some errors in the middle of the
> > AIO (nvme_aio_err()) for advanced retry.  Shouldn't AIO errors are
> > retry-able and supposed to be retried ?
> Sure, we can assume that receiving an error in the AIO callback means
> the lower layers exhausted available recovery mechanisms.

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