Garbage-collect the remaining vestiges of netisr.

Convert ARP from a legacy netisr to pktqueue.

if_attach and if_initialize cannot fail, don't test return value

These were originally made failable back in 2017 when if_initialize
allocated a softint in every interface for link state changes, so

if_attach and if_initialize cannot fail, don't test return value

These were originally made failable back in 2017 when if_initialize
allocated a softint in every interface for link state changes, so
that it could fail gracefully instead of panicking:

https://mail-index.NetBSD.org/source-changes/2017/10/23/msg089053.html

However, this spawned many seldom- or never-tested error branches,
which are risky to have around. And that softint in every interface
has since been replaced by a single global workqueue, because link
state changes require thread context but not low latency or high
throughput:

https://mail-index.NetBSD.org/source-changes/2020/02/06/msg113759.html

So there is no longer any reason for if_initialize to fail. (The
subroutine if_stats_init can't fail because percpu_alloc can't fail
either.)

There is a snag: the softint_establish in if_percpuq_create could
fail, potentially leading to bad consequences later on trying to use
the softint. This change doesn't introduce any new bugs because of
the snag -- if_percpuq_attach was already broken. However, the snag
can be better addressed without spawning error branches, either by
using a single softint or making softints less scarce.

(Separate commit will change the signatures of if_attach and
if_initialize to return void, scheduled to ride whatever is the next
convenient kernel bump.)

Patch and testing on amd64 and evbmips64-eb by maya@; commit message
soliloquy, and compile-testing on evbppc/i386/earmv7hf, by me.

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net: introduce IFQ_ENQUEUE_ISR to assemble packet queuing routines (NFCI)

Adopt <net/if_stats.h>.

Replace
m_copym(m, 0, M_COPYALL, M_DONTWAIT)
by
m_copypacket(m, M_DONTWAIT)
when it is clear that we are copying a packet (that has M_PKTHDR) and not
a raw mbuf chain.

m_copy -> m_copym

If if_attach() failed in the attach function, return.

Do ND in L2_output in the same manner as arpresolve

The benefits of this change are:
- The flow is consistent with IPv4 (and FreeBSD and OpenBSD)
- old: ip6_output => nd6_output (do ND if needed)

Do ND in L2_output in the same manner as arpresolve

The benefits of this change are:
- The flow is consistent with IPv4 (and FreeBSD and OpenBSD)
- old: ip6_output => nd6_output (do ND if needed) => L2_output (lookup a stored cache)
- new: ip6_output => L2_output (lookup a cache. Do ND if cache not found)
- We can remove some workarounds in nd6_output
- We can move L2 specific operations to their own place
- The performance slightly improves because one cache lookup is reduced

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Don't forget to free the mbuf when we decide not to reply to an ARP
request. This obviously is a terrible bug, since it allows a remote sender
to DoS the system with specially-crafted requests sent i

Don't forget to free the mbuf when we decide not to reply to an ARP
request. This obviously is a terrible bug, since it allows a remote sender
to DoS the system with specially-crafted requests sent in a loop.

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Get rid of unnecessary header inclusions

Fix race condition on ifqueue used by traditional netisr

If a underlying network device driver supports MSI/MSI-X, RX interrupts
can be delivered to arbitrary CPUs. This means that Layer 2 subroutin

Fix race condition on ifqueue used by traditional netisr

If a underlying network device driver supports MSI/MSI-X, RX interrupts
can be delivered to arbitrary CPUs. This means that Layer 2 subroutines
such as ether_input (softint) and subsequent Layer 3 subroutines (softint)
which are called via traditional netisr can be dispatched on an arbitrary
CPU. Layer 2 subroutines now run without any locks (expected) and so a
Layer 2 subroutine and a Layer 3 subroutine can run in parallel.

There is a shared data between a Layer 2 routine and a Layer 3 routine,
that is ifqueue and IF_ENQUEUE (from L2) and IF_DEQUEUE (from L3) on it
are racy now.

To fix the race condition, use ifqueue#ifq_lock to protect ifqueue
instead of splnet that is meaningless now.

The same race condition exists in route_intr. Fix it as well.

Reviewed by knakahara@

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Constify remaining rtentry of if_output (fix build)

IFQ_ENQUEUE refactor (3/3) : eliminate pktattr argument from IFQ_ENQUEUE caller

- tidy up error messages
- add a length argument to arpresolve()
- add KASSERT for overflow

Fix build

arpresolve() now returns 0 on success otherwise an error code.
Callers of arpresolve() now pass the error code back to their caller,
masking out EWOULDBLOCK.

This allows applications such as ping(8)

arpresolve() now returns 0 on success otherwise an error code.
Callers of arpresolve() now pass the error code back to their caller,
masking out EWOULDBLOCK.

This allows applications such as ping(8) to display a suitable error
condition.

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sprinkle _KERNEL_OPT

Pull out route lookups from L2 output routines

Route lookups for routes of RTF_GATEWAY were done in L2 output
routines such as ether_output, but they should be done in L3
i.e., before L2 output rout

Pull out route lookups from L2 output routines

Route lookups for routes of RTF_GATEWAY were done in L2 output
routines such as ether_output, but they should be done in L3
i.e., before L2 output routines. This change places the lookups
between L3 output routines (say ip_output) and the L2 output
routines.

The change is based on dyoung's patch submitted in the thread:
https://mail-index.netbsd.org/tech-net/2013/02/01/msg003847.html
You can find out detailed investigations by dyoung about the
issue in there.

Note that the change introduces a workaround for MPLS. ether_output
knew that it needs to fill the ethertype of a frame as MPLS,
based on a tag of an original route (rtentry), but now we don't
pass it to ehter_output. So we have to tell that in another way.
We use mtag to do so for now, which introduces some overhead.
We should fix it somehow in the future.

Discussed on tech-kern and tech-net.

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- Implement pktqueue interface for lockless IP input queue.
- Replace ipintrq and ip6intrq with the pktqueue mechanism.
- Eliminate kernel-lock from ipintr() and ip6intr().
- Some preparation work to

- Implement pktqueue interface for lockless IP input queue.
- Replace ipintrq and ip6intrq with the pktqueue mechanism.
- Eliminate kernel-lock from ipintr() and ip6intr().
- Some preparation work to push softnet_lock out of ipintr().

Discussed on tech-net.

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Put schednetisr() into splnet()/splx() pair.
This might avoids delay of processing a packet.

Add missing "\n" in log(9)

Push the bpf_ops usage back into bpf.h. Push the common ifp->if_bpf
check into the inline functions as well the fourth argument for
bpf_attach.

Redefine bpf linkage through an always present op vector, i.e.
#if NBPFILTER is no longer required in the client. This change
doesn't yet add support for loading bpf as a module, since drivers
can r

Redefine bpf linkage through an always present op vector, i.e.
#if NBPFILTER is no longer required in the client. This change
doesn't yet add support for loading bpf as a module, since drivers
can register before bpf is attached. However, callers of bpf can
now be modularized.

Dynamically loadable bpf could probably be done fairly easily with
coordination from the stub driver and the real driver by registering
attachments in the stub before the real driver is loaded and doing
a handoff. ... and I'm not going to ponder the depths of unload
here.

Tested with i386/MONOLITHIC, modified MONOLITHIC without bpf and rump.

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ar_tha() can return NULL; treat this as an error.