Re: lnc(4) driver ported from freebsd (le(4))

["Sepherosa Ziehau" <sepherosa@xxxxxxxxx>]

On 7/2/06, Bill Marquette <bill.marquette@xxxxxxxxx> wrote:
> I was interested in learning something about the kernel, so figured
> I'd take a crack at porting the le(4) driver that FreeBSD brought in
> from NetBSD - the ultimate goal is to bring pcn(4) from NetBSD over -
> the combination of the two drivers appears to be better than the
> existing lnc(4)/pcn(4) that Dragonfly has today (at least for VMWare)

VMware only uses lnc(4)

> and supports VLANs which the existing lnc(4) doesn't appear to (maybe
> I missed something).  As Dragonfly already has a le(4) driver and this
> was really a replacement for the existing lnc(4), I changed the driver
> name to lnc (functions and some defines are a little goofy right now
> because of it - looking for a little direction there).
>
> If there's interest, I'm looking for a little feedback on the port.  I
> know there's still some cleanup to do (and a man page update!), but
> more importantly:
>
> I borrowed the lock code from aac(4) - I'm not sure it's the "right
> way" to do things as it's the only driver that seems to use lock(9)
> functions - but it was the easiest one to use to see Dragonfly vs
> FreeBSD differences.
> I ifdef'd out FreeBSD-isms (I still have some cleaning to do there) -
> I'm not sure how that's treat in the Dragonfly tree, I only see a few
> instances of that in the network drivers, maybe that code should just
> go?

No extra lock is needed, all of the functions in "ifnet" struct are
called with ifp->if_serializer held, that means most functions in
network driver are protected by ifp->if_serializer (which you have
passed to bus_setup_intr() too).  So you can safely nuke most of the
LE_(UN)LOCK stuffs, except for "suspend", "resume", "shutdown" and
"detach", LE_(UN)LOCK should be changed to
lwkt_serializer_{enter,exit}() there (you can take a look to xl(4) for
example).  Special care should be taken for "detach": you should held
serializer for driver functions (e.g. lance_stop()) and
bus_teardown_intr(), while serializer should be released before
calling ether_ifdetach(), you can take a look at pcn_detach() for
example.  Since no callouts are used, there is nothing to worry about
the callout callback functions, otherwise the callback functions
should hold serializer too.

> FreeBSD has BUS_PROBE_LOW_PRIORITY to set bus priorities so drivers
> can pre-empt other drivers, I didn't see anything akin to that in
> Dragonfly (and sadly hardcoded the value - this needs to be cleaned up
> still).  The old driver defined LNC_PROBE_PRIORITY to -1, is that the
> "correct way" ? :)

Less than 0 is OK.


Thank you for the submission!!
If you can change the LE_(UN)LOCK stuffs, we can call for testing and
bring it into base soon.

Cheers,
sephe

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