Enforce that there are actually enough xenbus TX ring descriptors available
before attempting to queue the packet.

Comment tidyup; comment where the next explicit check should
appear.

Ensure that there are enough TX mbuf ring slots available before beginning
to dequeue a packet.

The tx path was trying to ensure that enough Xenbus TX ring slots existed but
it didn't check to see w

Ensure that there are enough TX mbuf ring slots available before beginning
to dequeue a packet.

The tx path was trying to ensure that enough Xenbus TX ring slots existed but
it didn't check to see whether the mbuf TX ring slots were also available.
They get freed in xn_txeof() which occurs after transmission, rather than earlier
on in the process. (The same happens under Linux too.)

Due to whatever reason (CPU use, scheduling, memory constraints, whatever) the
mbuf TX ring may not have enough slots free and would allocate slot 0. This is
used as the freelist head pointer to represent "free" mbuf TX ring slots; setting
this to an actual mbuf value rather than an id crashes the code.

This commit introduces some basic code to track the TX mbuf ring use and then
(hopefully!) ensures that enough slots are free in said TX mbuf ring before it
enters the actual work loop.

A few notes:

* Similar logic needs to be introduced to check there are enough actual slots
available in the xenbuf TX ring. There's some logic which is invoked earlier
but it doesn't hard-check against the number of available ring slots.
Its trivial to do; I'll do it in a subsequent commit.

* As I've now commented in the source, it is likely possible to deadlock the
driver under certain conditions where the rings aren't receiving any changes
(which I should enumerate) and thus Xen doesn't send any further software
interrupts. I need to make sure that the timer(s) are running right and
the queues are periodically kicked.

PR: 134926

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Do the invariant check before the mbuf is dereferenced.

Flesh out some inline documentation which hopefully reflect the intended
reality of these functions.

Add in some INVARIANT checks in the TX mbuf descriptor "freelist" management code.

Slot 0 must always remain "free" and be a pointer to the first free entry in the
mbuf descriptor list. It is thus a

Add in some INVARIANT checks in the TX mbuf descriptor "freelist" management code.

Slot 0 must always remain "free" and be a pointer to the first free entry in the
mbuf descriptor list. It is thus an error to have code allocate or push slot 0
back into the list.

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Merge from HEAD

The merge in r189699 reverted part of the work done in a previous commit
(r188036.)

Re-revert that change so the Xen networking functions again.

Update the projects tree to a newer FreeBSD current.

Merge in support for Xen HVM on amd64 architecture.

fix non-witness compile

break out of loop if we run out of mbufs

merge 186535, 186537, and 186538 from releng_7_xen

Log:
- merge in latest xenbus from dfr's xenhvm
- fix race condition in xs_read_reply by converting tsleep to mtx_sleep

Log:
unmask evtchn in b

merge 186535, 186537, and 186538 from releng_7_xen

Log:
- merge in latest xenbus from dfr's xenhvm
- fix race condition in xs_read_reply by converting tsleep to mtx_sleep

Log:
unmask evtchn in bind_{virq, ipi}_to_irq

Log:
- remove code for handling case of not being able to sleep
- eliminate tsleep - make sleeps atomic

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Integrate 185578 from dfr
Use newbus to managed devices

Don't call ether_ioctl() with locks held. Loop in xn_rxeof() until the backend
stops adding stuff to the ring otherwise we miss RX interrupts which kills
performance.

Update xen/interface includes to the latest in mercurial

MFC after: 1 month

reflect header change in netfront

MFC after: 1 month

For reasons that I have not delved in to Xen 3.2 netback now does header splitting
so packets > 128 bytes are now split in to multiple buffer. This fixes netfront
to handle multiple buffers per rx pa

For reasons that I have not delved in to Xen 3.2 netback now does header splitting
so packets > 128 bytes are now split in to multiple buffer. This fixes netfront
to handle multiple buffers per rx packet.

MFC after: 1 month

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change netfront to match xen31_6
fix console locking

include vmparam.h for KERNBASE and fix typo

register netfront before xenbus does its probing

MFC after: 1 month

Import Xen paravirtual drivers.

MFC after: 2 weeks