Re: [RFC PATCH net-next v5 2/2] net: add netmem to skb_frag_t

[Jason Gunthorpe]

On Mon, Jan 15, 2024 at 03:23:33PM -0800, Mina Almasry wrote:
> > > You did not answer my question that I asked here, and ignoring this
> > > question is preventing us from making any forward progress on this
> > > discussion. What do you expect or want skb_frag_page() to do when
> > > there is no page in the frag?
> >
> > I would expect it to do nothing.
> 
> I don't understand. skb_frag_page() with an empty implementation just
> results in a compiler error as the function needs to return a page
> pointer. Do you actually expect skb_frag_page() to unconditionally
> cast frag->netmem to a page pointer? That was explained as
> unacceptable over and over again by Jason and Christian as it risks
> casting devmem to page; completely unacceptable and will get nacked.
> Do you have a suggestion of what skb_frag_page() should do that will
> not get nacked by mm?

WARN_ON and return NULL seems reasonable?

Jason