On Apr 20, 2010, at 5:55 PM, Luigi Rizzo wrote:
On Tue, Apr 20, 2010 at 07:28:45PM +0200, Luigi Rizzo wrote:
just noticed that sys/kern/uipc_domain.c still sets max_linkhdr=16
as a default.
The value is often used to reserve head space in mbufs for
the MAC header. As such, 16 is too short for systems that make
use of vlans, and the effect might be that we would need
additional mbuf entries or at least move stuff down
as the vlan tag is added.
Any objection to bumping the default to 20 ?
forgot to mention:
max_linkhdr is available as a sysctl, kern.max_linkhdr , but other
than that, there is no code in sys/ that sets the value, so systems
are stuck at 16 unless users override the default.
We need a coherent way to handle max_linkhdr. I hacked it in net80211
to insure bridged 802.11 frames have sufficient contiguous space in
the mbufs but never did something like define an api and generate
events/callbacks on changes. Last I looked doing this right was non-
trivial.
Sam
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