[PATCH v2] udhcp: add option to set CoS priority

[pacien]

I worked on my own version of this, before seeing that this one was
already posted to the list. Sorry for the collision.

Message-Id: <20230410214157.1017054-1-dzfkct.busyboxml at pacien.net>

It differs mainly in the terminology: it talks about the SKB priority
instead of the CoS. Though it should perhaps be the "socket priority"
instead? The VLAN CoS mapping isn't automatic.

It also differs a bit in the way errors are handled, and puts the
priority in the client_data struct with the rest of the settings.

<peron.clem at gmail.com>:
> I'm still testing this patch and I'm unsure if we need to set the
> priority for all the sockets.
> [...]
> udhcp_send_raw_packet() set the priority and not
> udhcp_send_kernel_packet().

It seems that the former is used for multicast, the latter for unicast,
used in particular for renew and release. So things should probably be
kept consistent here.

<rep.dot.nop at gmail.com>:
> > > +//usage:     "\n       -y PRIORITY     CoS value 0 .. 7, default 0"
>
> I don't see that you would cap the value to 7 anywhere, do you?
> The manpage seems to imply that 0..6 can be used by unprivileged users,
> higher values require CAP_NET_ADMIN which is fine per se; I assume the
> kernel does enough sanity-checking so we can attempt to pass whatever
> the user said.

I believe 0 to 7 would correspond to VLAN CoS (PCP)?
Though that should not be limited here for the socket priority.

--
Pacien TRAN-GIRARD <pacien.trangirard at pacien.net>