Re: [PATCH] hw/nvme: actually implement abort

[Klaus Jensen]

On Jul  2 09:24, Keith Busch wrote:
> On Tue, Jul 02, 2024 at 01:32:32PM +0530, Ayush Mishra wrote:
> > Abort was not implemented previously, but we can implement it for AERs and 
> > asynchrnously for I/O.
> 
> Not implemented for a reason. The target has no idea if the CID the
> host requested to be aborted is from the same context that the target
> has. Target may have previoulsy completed it, and the host re-issued a
> new command after the abort, and due to the queueing could have been
> observed in a different order, and now you aborted the wrong command.

I might be missing something here, but are you saying that the Abort
command is fundamentally flawed? Isn't this a host issue? The Abort is
for a specific CID on a specific SQID. The host *should* not screw this
up and reuse a CID it has an outstanding Abort on?

I don't think there are a lot of I/O commands that a host would be able
to cancel (in QEMU, not at all, because only the iscsi backend
actually implements blk_aio_cancel_async). But some commands that issue
multiple AIOs, like Copy, may be long running and with this it can
actually be cancelled.

And with regards to AERs, I don't see why it is not advantageous to be
able to Abort one?

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