Re: [PATCH] nvme: uring_cmd specific request_queue for SGLs

[Keith Busch <kbusch@kernel.org>]

On Tue, Jul 01, 2025 at 08:16:09AM +0200, Christoph Hellwig wrote:
> On Mon, Jun 30, 2025 at 08:04:47AM -0600, Keith Busch wrote:
> > 
> >   a. Force the application to split each iovec into a separate command
> > 
> >   b. Relax the kernel's limits to match the hardware's capabilities
> > 
> > This patch is trying to do "b".
> 
> a, or a variant of that (not using passthrough) would in general be
> my preference.  Why is that not suitable here?

Why use passthrough? Because until very recently (as in the current rc),
passthrough had been the only way for user space to access write streams
and metadata.

We've had uring_cmd passthrough for several years now, so there's some
decently mature applications making use of it. But can they split
commands such that they dispatch one per iovec instead of as a single
command? I've asked that, still waiting to hear back. I sent this patch,
though, because they bought SGL capable hardware specifically so they
could do this.