Must dev->set_multicast_list() complete before returning?

Must dev->set_multicast_list() complete before returning?

[Rask Ingemann Lambertsen]

Hi.

Must dev->set_multicast_list() complete the configuration of a network device before returning?

Regards,
Rask Ingemann Lambertsen

Re: Must dev->set_multicast_list() complete before returning?

[Donald Becker]

On Tue, 1 Apr 2003, Rask Ingemann Lambertsen wrote:

> Must dev->set_multicast_list() complete the configuration of a network
> device before returning? 

The promiscuous setting must complete before return, but there are
several drivers where the updated multicast filter does not immediately
take effect.

I have not seen hardware where setting promiscuous mode is a queued
command.  If you have such hardware, you may have to do some extra
software filtering and accept missing some packets during transitions.

-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993

Re: Must dev->set_multicast_list() complete before returning?

[Rask Ingemann Lambertsen]

Donald Becker wrote:

> The promiscuous setting must complete before return, but there are
> several drivers where the updated multicast filter does not immediately
> take effect.
> 
> I have not seen hardware where setting promiscuous mode is a queued
> command.

Intel i82586, i82596 and, as far as I can tell from other drivers, several other Intel i825xx Ethernet chips. IIRC, the function must not sleep. That means busy-wait for it to complete. :-(

Regards,
Rask Ingemann Lambertsen

Re: Must dev->set_multicast_list() complete before returning?

[David Brownell]

Donald Becker wrote:
> 
> I have not seen hardware where setting promiscuous mode is a queued
> command.  If you have such hardware, you may have to do some extra
> software filtering and accept missing some packets during transitions.

Every USB network adapter will need to queue such commands,
unless they don't support such operations at all.  So you
have probably seen such hardware, without realizing it!

I just looked ... none of them do any extra filtering.

- Dave

Re: Must dev->set_multicast_list() complete before returning?

[Donald Becker]

On Wed, 2 Apr 2003, David Brownell wrote:

> Donald Becker wrote:
> > 
> > I have not seen hardware where setting promiscuous mode is a queued
> > command.  If you have such hardware, you may have to do some extra
> > software filtering and accept missing some packets during transitions.
> 
> Every USB network adapter will need to queue such commands,
> unless they don't support such operations at all.  So you
> have probably seen such hardware, without realizing it!

Errrm, a previous message pointed out to me that there were several
other Intel chips that _I had written drivers for_ that queue commands.
And yes, I had also forgotten about bridged NICs such as USB (which I've
also written drivers for).

> I just looked ... none of them do any extra filtering.

I've not added extra filtering to any driver USB or otherwise.

It may be that there is a problem here that is rarely encountered and
never identified as a problem.  A filter change from promiscuous to
normal mode is at worst a narrow window.
The atp.c driver is special because it put the hardware into promiscuous
mode for allmulti, and thus any potential problem became a continuous
issue.

Alan, do you remember what piece of code had a problem with unicast
packets to other hosts that would normally be filtered out by the
hardware?  It may be that issue is gone with 2.4 and later kernels.
(Multicast is not an issue because most chips use an imperfect hash
filter and thus the kernel has always needed additional filtering.)

-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993