[PATCH] Fix for using NFS root with if_arge

[Patrick Kelsey]

This patch fixes an issue I encountered using an NFS root with an
ar71xx-based MikroTik RouterBoard 450G on -current where the kernel fails
to contact a DHCP/BOOTP server via if_arge when it otherwise should be able
to.  This may be the same issue that Monthadar Al Jaberi reported against
an RSPRO on 6 March, as the signature is the same:

%%%

DHCP/BOOTP timeout for server 255.255.255.255
DHCP/BOOTP timeout for server 255.255.255.255
DHCP/BOOTP timeout for server 255.255.255.255
.
.
.
DHCP/BOOTP timeout for server 255.255.255.255
DHCP/BOOTP timeout for server 255.255.255.255
arge0: initialization failed: no memory for rx buffers
DHCP/BOOTP timeout for server 255.255.255.255
arge0: initialization failed: no memory for rx buffers

%%%

The primary issue that I found is that the DHCP/BOOTP message that
bootpc_call() is sending never makes it onto the wire, which I believe is
due to the following:

- Last December, a change was made to the ifioctl that bootpc_call() uses
to adjust the netmask around the sosend().

- The new ioctl (SIOCAIFADDR) performs an if_init when invoked, whereas the
old one (SIOCSIFNETMASK) did not.

- if_arge maintains its own sense of link state in sc->arge_link_status.

- On a single-phy interface, sc->arge_link_status is initialized to 0 in
arge_init_locked().

- sc->arge_link_status remains 0 until a phy state change notification
causes arge_link_task to run, notice the link is up, and set it to 1.

- The inits caused by the ifioctls in bootpc_call are reinitializing the
interface, but not the phy, so sc->arge_link_status goes to 0 and remains
there.

- arge_start_locked() always sees sc->arge_link_status == 0 and returns
without queuing anything.


The attached patch changes arge_init_locked() such that in the single-phy
case, instead of initializing sc->arge_link_status to 0, it runs
arge_link_task() to set it according to the current phy state.  This change
has allowed my setup to mount an NFS root successfully.

I think there is a secondary issue here regarding the "arge0:
initialization failed: no memory for rx buffers".  I have not dug into it
completely yet, but at first blush it seems that arge_stop() leaks mbufs
from the rx ring, so after some number of arge_init() calls (in this case
triggered by the DHCP/BOOTP message timeouts), all mbufs are exhausted.

-Patrick
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