Re: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx timestamp directly from interrupt for i210

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-02-09 07:46:01 [-0500], Willem de Bruijn wrote:
> > > Yeah, but what is the legacy user here? If you enable HW-timestamps but
> > > never set OPT_TSONLY and the sysctl is also 0 then you reply on the
> > > CAP_NET_RAW later on. Right?
> > 
> > Legacy users here means users of HW TX timestamps expecting full skb to 
> > be returned back with the TX timestamp. Legacy here means that skb will 
> > be returned with headers modified by stack, which is kind of exposure of
> > data, which requires CAP_NET_RAW...

Ah okay. I assumed the err-queue was the standard way of receiving
timestamps.

> > > I just try to justify the CAP_NET_RAW check and if it is required to
> > > move it earlier (where HW timestamps are enabled). And if the sysctl
> > > check is enough then maybe it is not needed.
> > 
> > Capabilities should not change during lifetime of the process, should be
> > fine to move. On the other, sysctl can be changed system-wide which may 
> > affect users.
> 
> Ignore the hardware configuration. That is entirely optional. Some
> devices will timestamp every packet.
> 
> The capability check here is per-socket, independent from the system
> hardware configuration.
> 
> I don't see how it could be moved.
> 
> Before OPT_TSONLY was introduced packets were always queued with their
> payload. The sysctl check was added to optionally disallow this. The
> check could arguably be moved earlier in the socket lifecycle and the
> decision cached in the socket. But then flipping the sysctl would not
> affect existing sockets, so that is a change in ABI behavior.

You could cache only the part under sk_callback_lock.
Any other suggestions?
The access from IRQ is quick and avoids any detours.
The alternative would be to move the whole routine into an aux_worker.
For every driver doing it from the IRQ handler.

Sebastian