linux-kernel - Re: [PATCH net-next v18 07/14] memory-provider: dmabuf devmem memory provider

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Message-ID: <20240812165708.33234ed6@kernel.org>
Date: Mon, 12 Aug 2024 16:57:08 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
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Subject: Re: [PATCH net-next v18 07/14] memory-provider: dmabuf devmem
 memory provider

On Mon, 12 Aug 2024 20:10:39 +0100 Pavel Begunkov wrote:
> > 1. Drivers need to be able to say "I support unreadable netmem".
> > Failure to report unreadable netmem support should cause the netlink
> > API to fail when the user tries to bind dmabuf/io uring memory.
> > 
> > 2. Drivers need to be able to say "I want a header pool (with readable
> > netmem)" or "I want a data pool (potentially with unreadable netmem)".
> > 
> > Pavel is suggesting implementing both of these in 2 different flags.
> > 
> > Jakub is suggesting implementing both with 1 flag which says "I can
> > support unreadable netmem for this pool" , and guarding against #1
> > with a refcount check to detect if a dmabuf pool should have been
> > created but wasn't.  
> 
> That would be iffy IIUC, but I think Jakub just explicitly said
> that the refcount trick was just for debugging purposes and not
> for gauging errors like "providers are not supported by the driver".
> 
> "Yup, the refcount (now: check of the page pool list) was meant
> as a WARN_ONCE() to catch bad drivers."

Sorry, insufficient caffeine level in the morning.
We can't WARN_ONCE(), indeed.