Re: [RFC PATCH] nvme: replace lazy sgl warn with informational message

[Keith Busch <kbusch@kernel.org>]

On Fri, Jan 31, 2025 at 10:06:24AM +0200, Sagi Grimberg wrote:
> On 31/01/2025 9:48, Christoph Hellwig wrote:
> > On Thu, Jan 30, 2025 at 09:51:31AM -0800, Keith Busch wrote:
> > > From: Keith Busch <kbusch@kernel.org>
> > > 
> > > Instead of warning about the device's SGL capabilities the first time we
> > > consider using them with a passthrough command, print out what the
> > > device is capable of during initialization. While we're at it, print
> > > other interesting capabilities that may be useful to know when you just
> > > have a dmesg. The ouput format was inspired by other existing subsystems
> > > like pci.
> > > 
> > > And example of the new message when used with a default qemu nvme
> > > emulated device:
> > > 
> > >    nvme nvme0: sgl+ meta-sgl+ sed- vwc+ apst- dsm+ wz+
> > Printing out the capabilities sounds really useful.  But I don't see
> > how this is useful for replacing the warning about the unchecked
> > passthrough?

I thought this patch could remove the message because it tells you
upfront what you'll get if you use the passthrough interface. The
existing message tells you what you're getting once you actually try to
use it, so they felt a bit redundant.

> I agree, I'd keep the warn_once messages.

Okay. The problem with the message is that it's a new warn, but nothing
has really changed as far as what the driver supports, so having it at
the "warn" level caused some alarm. Any concern if it's an info_once
instead? I just want to avoid repeat explanations on its implications;
I've experienced several offlist discussions about it already.