On Fri, Jul 24, 2026 at 07:24:19AM -0700, Jakub Kicinski wrote:
> On Thu, 23 Jul 2026 16:58:14 -0700 Bobby Eshleman wrote:
> > > > + if (info->attrs[NETDEV_A_DMABUF_RX_BUF_SIZE]) {
> > > > + u32 rx_buf_size =
> > > > nla_get_u32(info->attrs[NETDEV_A_DMABUF_RX_BUF_SIZE]);
> > > > +
> > > > + if (!rx_buf_size || !is_power_of_2(rx_buf_size) ||
> > > > + rx_buf_size < PAGE_SIZE) {
> > >
> > > we should add a check: min: page-size in the Netlink policy?
> >
> > I played around with this adding:
> >
> > Documentation/netlink/specs/netdev.yaml:
> > definitions:
> > + -
> > + type: const
> > + name: page-size
> > + value: 4096 # dummy value, to pass ynl_gen_c.py checks
> > + header: asm/page.h
> > + scope: kernel
> >
> > Generating:
> >
> > +static const struct netlink_range_validation
> > netdev_a_dmabuf_rx_page_size_range = {
> > + .min = PAGE_SIZE,
> > + .max = U32_MAX,
> > +};
> > +
> >
> > ... but the dummy 4096 is kind of annoying. ynl_gen_c.py can't know the
> > value of PAGE_SIZE but needs some value for its arithmetic checks (e.g.,
> > confirm min < max is true).
> >
> > Should we stick with using a dummy value, or should we add a patch
> > teaching ynl_gen_c.py to allow value-less consts (skip the arithmetic
> > checks)?
>
> Let's stick to a dummy one for now, but maybe something obviously dummy
> like 0 ?
0 sounds good to me.
>
> BTW did you add both min and max checks? Cause the only risk with using
> a dummy value would be that the policy will be rendered inline, and
> inline policy is u16 so 64k wouldn't fit. But your sample above has a
> max of u32_max which forces the out-of-line policy, which is what we
> want.
Yep, u32_max:
+ name: rx-page-size
...
+ checks:
+ min: page-size
+ max: u32-max
Sorry, probably should have just sent the whole patch instead of
replying hunk-by-hunk.
BTW, how expressive do we want these policies? For example, would
absorbing the power_of_2 check into a policy be valid in the future? or
is that too bespoke?
Best,
Bobby
