This patch (as1241) renames a bunch of functions in the PM core.
Rather than go through a boring list of name changes, suffice it to
say that in the end we have a bunch of pairs of functions:

	device_resume_noirq	dpm_resume_noirq
	device_resume		dpm_resume
	device_complete		dpm_complete
	device_suspend_noirq	dpm_suspend_noirq
	device_suspend		dpm_suspend
	device_prepare		dpm_prepare

in which device_X does the X operation on a single device and dpm_X
invokes device_X for all devices in the dpm_list.

In addition, the old dpm_power_up and device_resume_noirq have been
combined into a single function (dpm_resume_noirq).

Lastly, dpm_suspend_start and dpm_resume_end are the renamed versions
of the former top-level device_suspend and device_resume routines.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Rename the functions performing "_noirq" dev_pm_ops
operations from device_power_down() and device_power_up()
to device_suspend_noirq() and device_resume_noirq().

The new function names are chosen to show that the functions
are responsible for calling the _noirq() versions to finalize
the suspend/resume operation. The current function names do
not perform power down/up anymore so the names may be misleading.

Global function renames:
- device_power_down() -> device_suspend_noirq()
- device_power_up() -> device_resume_noirq()

Static function renames:
- suspend_device_noirq() -> __device_suspend_noirq()
- resume_device_noirq() -> __device_resume_noirq()
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-by: Len Brown <lenb@kernel.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

This patch removes unused asm/suspend.h files for
the following architectures:

 alpha, arm, ia64, m68k, mips, s390, um
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

This is the last unification step. Here we do remove one of the files
and rename the left one as cpu.c, as both are now the same.
Also update power/Makefile, telling it to build cpu.o, instead of
cpu_(32|64).o
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

In this step, we do unify the copyright notes for both files
cpu_32.c and cpu_64.c, making such files exactly the same.
It's the last step before the actual unification, that will
rename one of them to cpu.c and remove the other one.
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

In this step we do unify cpu_32.c and cpu_64.c functions that
work on restoring the saved processor state. Also, we do
eliminate the forward declaration of fix_processor_context()
for X86_64, as it's not needed anymore.
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

In this step we do unify cpu_32.c and cpu_64.c functions that
work on saving the processor state.
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Aiming total unification of cpu_32.c and cpu_64.c, in this step
we do unify the global variables and existing forward declarations
for such files.
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

First step towards the unification of cpu_32.c and cpu_64.c.
This commit unifies the headers of such files, making both
of them use the same header files. It also remove the uneeded
<module.h>.
Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Signed-off-by: Lauro Salmito <laurosalmito@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Sysdevs have to be suspended and resumed with interrupts disabled and
things usually break in a way that's difficult to debug if one of
sysdev drivers enables interrupts by mistake during suspend or
resume.  Add extra checks that will generate warnings in such cases.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

One of the numbers in arch/x86/kernel/acpi/sleep.c is long, but it is
not annotated appropriately, so sparese warns about it.  Fix that.

[rjw: added the changelog.]
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6: (290 commits)
  ALSA: pcm - Update document about xrun_debug proc file
  ALSA: lx6464es - support standard alsa module parameters
  ALSA: snd_usb_caiaq: set mixername
  ALSA: hda - add quirk for STAC92xx (SigmaTel STAC9205)
  ALSA: use card device as parent for jack input-devices
  ALSA: sound/ps3: Correct existing and add missing annotations
  ALSA: sound/ps3: Restructure driver source
  ALSA: sound/ps3: Fix checkpatch issues
  ASoC: Fix lm4857 control
  ALSA: ctxfi - Clear PCM resources at hw_params and hw_free
  ALSA: ctxfi - Check the presence of SRC instance in PCM pointer callbacks
  ALSA: ctxfi - Add missing start check in atc_pcm_playback_start()
  ALSA: ctxfi - Add use_system_timer module option
  ALSA: usb - Add boot quirk for C-Media 6206 USB Audio
  ALSA: ctxfi - Fix wrong model id for UAA
  ALSA: ctxfi - Clean up probe routines
  ALSA: hda - Fix the previous tagra-8ch patch
  ALSA: hda - Add 7.1 support for MSI GX620
  ALSA: pcm - A helper function to compose PCM stream name for debug prints
  ALSA: emu10k1 - Fix minimum periods for efx playback
  ...

* topic/ps3:
  ALSA: sound/ps3: Correct existing and add missing annotations
  ALSA: sound/ps3: Restructure driver source
  ALSA: sound/ps3: Fix checkpatch issues

* topic/pcm-jiffies-check:
  ALSA: pcm - Update document about xrun_debug proc file

* topic/misc:
  ALSA: use card device as parent for jack input-devices

* topic/lx6464es:
  ALSA: lx6464es - support standard alsa module parameters

* topic/hda:
  ALSA: hda - add quirk for STAC92xx (SigmaTel STAC9205)

* topic/caiaq:
  ALSA: snd_usb_caiaq: set mixername

* topic/asoc:
  ASoC: Fix lm4857 control

Merge branch 'topic/slab/earlyboot-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6

* 'topic/slab/earlyboot-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6:
  slab: setup cpu caches later on when interrupts are enabled
  slab,slub: don't enable interrupts during early boot
  slab: fix gfp flag in setup_cpu_cache()
  x86: make zap_low_mapping could be used early
  irq: slab alloc for default irq_affinity
  memcg: fix page_cgroup fatal error in FLATMEM

* git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6: (154 commits)
  [SCSI] osd: Remove out-of-tree left overs
  [SCSI] libosd: Use REQ_QUIET requests.
  [SCSI] osduld: use filp_open() when looking up an osd-device
  [SCSI] libosd: Define an osd_dev wrapper to retrieve the request_queue
  [SCSI] libosd: osd_req_{read,write} takes a length parameter
  [SCSI] libosd: Let _osd_req_finalize_data_integrity receive number of out_bytes
  [SCSI] libosd: osd_req_{read,write}_kern new API
  [SCSI] libosd: Better printout of OSD target system information
  [SCSI] libosd: OSD2r05: Attribute definitions
  [SCSI] libosd: OSD2r05: Additional command enums
  [SCSI] mpt fusion: fix up doc book comments
  [SCSI] mpt fusion: Added support for Broadcast primitives Event handling
  [SCSI] mpt fusion: Queue full event handling
  [SCSI] mpt fusion: RAID device handling and Dual port Raid support is added
  [SCSI] mpt fusion: Put IOC into ready state if it not already in ready state
  [SCSI] mpt fusion: Code Cleanup patch
  [SCSI] mpt fusion: Rescan SAS topology added
  [SCSI] mpt fusion: SAS topology scan changes, expander events
  [SCSI] mpt fusion: Firmware event implementation using seperate WorkQueue
  [SCSI] mpt fusion: rewrite of ioctl_cmds internal generated function
  ...

* git://git.infradead.org/~dwmw2/firmware-2.6:
  firmware: speed up request_firmware(), v3

* git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-2.6-nmw:
  GFS2: Remove lock_kernel from gfs2_put_super()
  GFS2: Add tracepoints

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-lguest: (31 commits)
  lguest: add support for indirect ring entries
  lguest: suppress notifications in example Launcher
  lguest: try to batch interrupts on network receive
  lguest: avoid sending interrupts to Guest when no activity occurs.
  lguest: implement deferred interrupts in example Launcher
  lguest: remove obsolete LHREQ_BREAK call
  lguest: have example Launcher service all devices in separate threads
  lguest: use eventfds for device notification
  eventfd: export eventfd_signal and eventfd_fget for lguest
  lguest: allow any process to send interrupts
  lguest: PAE fixes
  lguest: PAE support
  lguest: Add support for kvm_hypercall4()
  lguest: replace hypercall name LHCALL_SET_PMD with LHCALL_SET_PGD
  lguest: use native_set_* macros, which properly handle 64-bit entries when PAE is activated
  lguest: map switcher with executable page table entries
  lguest: fix writev returning short on console output
  lguest: clean up length-used value in example launcher
  lguest: Segment selectors are 16-bit long. Fix lg_cpu.ss1 definition.
  lguest: beyond ARRAY_SIZE of cpu->arch.gdt
  ...

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-virtio:
  virtio: enhance id_matching for virtio drivers
  virtio: fix id_matching for virtio drivers
  virtio: handle short buffers in virtio_rng.
  virtio_blk: add missing __dev{init,exit} markings
  virtio: indirect ring entries (VIRTIO_RING_F_INDIRECT_DESC)
  virtio: teach virtio_has_feature() about transport features
  virtio: expose features in sysfs
  virtio_pci: optional MSI-X support
  virtio_pci: split up vp_interrupt
  virtio: find_vqs/del_vqs virtio operations
  virtio: add names to virtqueue struct, mapping from devices to queues.
  virtio: meet virtio spec by finalizing features before using device
  virtio: fix obsolete documentation on probe function

* 'cuse' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse:
  CUSE: implement CUSE - Character device in Userspace
  fuse: export symbols to be used by CUSE
  fuse: update fuse_conn_init() and separate out fuse_conn_kill()
  fuse: don't use inode in fuse_file_poll
  fuse: don't use inode in fuse_do_ioctl() helper
  fuse: don't use inode in fuse_sync_release()
  fuse: create fuse_do_open() helper for CUSE
  fuse: clean up args in fuse_finish_open() and fuse_release_fill()
  fuse: don't use inode in helpers called by fuse_direct_io()
  fuse: add members to struct fuse_file
  fuse: prepare fuse_direct_io() for CUSE
  fuse: clean up fuse_write_fill()
  fuse: use struct path in release structure
  fuse: misc cleanups

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-module-and-param:
  module: cleanup FIXME comments about trimming exception table entries.
  module: trim exception table on init free.
  module: merge module_alloc() finally
  uml module: fix uml build process due to this merge
  x86 module: merge the rest functions with macros
  x86 module: merge the same functions in module_32.c and module_64.c
  uvesafb: improve parameter handling.
  module_param: allow 'bool' module_params to be bool, not just int.
  module_param: add __same_type convenience wrapper for __builtin_types_compatible_p
  module_param: split perm field into flags and perm
  module_param: invbool should take a 'bool', not an 'int'
  cyber2000fb.c: use proper method for stopping unload if CONFIG_ARCH_SHARK

* 'for-2.6.31' of git://git.kernel.org/pub/scm/linux/kernel/git/bart/ide-2.6: (29 commits)
  ide: re-implement ide_pci_init_one() on top of ide_pci_init_two()
  ide: unexport ide_find_dma_mode()
  ide: fix PowerMac bootup oops
  ide: skip probe if there are no devices on the port (v2)
  sl82c105: add printk() logging facility
  ide-tape: fix proc warning
  ide: add IDE_DFLAG_NIEN_QUIRK device flag
  ide: respect quirk_drives[] list on all controllers
  hpt366: enable all quirks for devices on quirk_drives[] list
  hpt366: sync quirk_drives[] list with pdc202xx_{new,old}.c
  ide: remove superfluous SELECT_MASK() call from do_rw_taskfile()
  ide: remove superfluous SELECT_MASK() call from ide_driveid_update()
  icside: remove superfluous ->maskproc method
  ide-tape: fix IDE_AFLAG_* atomic accesses
  ide-tape: change IDE_AFLAG_IGNORE_DSC non-atomically
  pdc202xx_old: kill resetproc() method
  pdc202xx_old: don't call pdc202xx_reset() on IRQ timeout
  pdc202xx_old: use ide_dma_test_irq()
  ide: preserve Host Protected Area by default (v2)
  ide-gd: implement block device ->set_capacity method (v2)
  ...

Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86: Provide _sdata in the vmlinux.lds.S file
  x86: handle initrd that extends into unusable memory

Fixes the following boot-time warning:

  [    0.000000] ------------[ cut here ]------------
  [    0.000000] WARNING: at kernel/smp.c:369 smp_call_function_many+0x56/0x1bc()
  [    0.000000] Hardware name:
  [    0.000000] Modules linked in:
  [    0.000000] Pid: 0, comm: swapper Not tainted 2.6.30 #492
  [    0.000000] Call Trace:
  [    0.000000]  [<ffffffff8149e021>] ? _spin_unlock+0x4f/0x5c
  [    0.000000]  [<ffffffff8108f11b>] ? smp_call_function_many+0x56/0x1bc
  [    0.000000]  [<ffffffff81061764>] warn_slowpath_common+0x7c/0xa9
  [    0.000000]  [<ffffffff810617a5>] warn_slowpath_null+0x14/0x16
  [    0.000000]  [<ffffffff8108f11b>] smp_call_function_many+0x56/0x1bc
  [    0.000000]  [<ffffffff810f3e00>] ? do_ccupdate_local+0x0/0x54
  [    0.000000]  [<ffffffff810f3e00>] ? do_ccupdate_local+0x0/0x54
  [    0.000000]  [<ffffffff8108f2be>] smp_call_function+0x3d/0x68
  [    0.000000]  [<ffffffff810f3e00>] ? do_ccupdate_local+0x0/0x54
  [    0.000000]  [<ffffffff81066fd8>] on_each_cpu+0x31/0x7c
  [    0.000000]  [<ffffffff810f64f5>] do_tune_cpucache+0x119/0x454
  [    0.000000]  [<ffffffff81087080>] ? lockdep_init_map+0x94/0x10b
  [    0.000000]  [<ffffffff818133b0>] ? kmem_cache_init+0x421/0x593
  [    0.000000]  [<ffffffff810f69cf>] enable_cpucache+0x68/0xad
  [    0.000000]  [<ffffffff818133c3>] kmem_cache_init+0x434/0x593
  [    0.000000]  [<ffffffff8180987c>] ? mem_init+0x156/0x161
  [    0.000000]  [<ffffffff817f8aae>] start_kernel+0x1cc/0x3b9
  [    0.000000]  [<ffffffff817f829a>] x86_64_start_reservations+0xaa/0xae
  [    0.000000]  [<ffffffff817f837f>] x86_64_start_kernel+0xe1/0xe8
  [    0.000000] ---[ end trace 4eaa2a86a8e2da22 ]---

Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

As explained by Benjamin Herrenschmidt:

  Oh and btw, your patch alone doesn't fix powerpc, because it's missing
  a whole bunch of GFP_KERNEL's in the arch code... You would have to
  grep the entire kernel for things that check slab_is_available() and
  even then you'll be missing some.

  For example, slab_is_available() didn't always exist, and so in the
  early days on powerpc, we used a mem_init_done global that is set form
  mem_init() (not perfect but works in practice). And we still have code
  using that to do the test.

Therefore, mask out __GFP_WAIT, __GFP_IO, and __GFP_FS in the slab allocators
in early boot code to avoid enabling interrupts.
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

Fixes the following warning during bootup when compiling with CONFIG_SLAB:

  [    0.000000] ------------[ cut here ]------------
  [    0.000000] WARNING: at kernel/lockdep.c:2282 lockdep_trace_alloc+0x91/0xb9()
  [    0.000000] Hardware name:
  [    0.000000] Modules linked in:
  [    0.000000] Pid: 0, comm: swapper Not tainted 2.6.30 #491
  [    0.000000] Call Trace:
  [    0.000000]  [<ffffffff81087d84>] ? lockdep_trace_alloc+0x91/0xb9
  [    0.000000]  [<ffffffff81061764>] warn_slowpath_common+0x7c/0xa9
  [    0.000000]  [<ffffffff810617a5>] warn_slowpath_null+0x14/0x16
  [    0.000000]  [<ffffffff81087d84>] lockdep_trace_alloc+0x91/0xb9
  [    0.000000]  [<ffffffff810f5b03>] kmem_cache_alloc_node_notrace+0x26/0xdf
  [    0.000000]  [<ffffffff81487f4e>] ? setup_cpu_cache+0x7e/0x210
  [    0.000000]  [<ffffffff81487fe3>] setup_cpu_cache+0x113/0x210
  [    0.000000]  [<ffffffff810f73ff>] kmem_cache_create+0x409/0x486
  [    0.000000]  [<ffffffff818131c1>] kmem_cache_init+0x232/0x593
  [    0.000000]  [<ffffffff8180987c>] ? mem_init+0x156/0x161
  [    0.000000]  [<ffffffff817f8aae>] start_kernel+0x1cc/0x3b9
  [    0.000000]  [<ffffffff817f829a>] x86_64_start_reservations+0xaa/0xae
  [    0.000000]  [<ffffffff817f837f>] x86_64_start_kernel+0xe1/0xe8
  [    0.000000] ---[ end trace 4eaa2a86a8e2da22 ]---
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

Conflicts:
	drivers/message/fusion/mptsas.c

fixed up conflict between req->data_len accessors and mptsas driver updates.
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

Support the VIRTIO_RING_F_INDIRECT_DESC feature.

This is a simple matter of changing the descriptor walking
code to operate on a struct vring_desc* and supplying it
with an indirect table if detected.
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

The Guest only really needs to tell us about activity when we're going
to listen to the eventfd: normally, we don't want to know.

So if there are no available buffers, turn on notifications, re-check,
then wait for the Guest to notify us via the eventfd, then turn
notifications off again.

There's enough else going on that the differences are in the noise.

Before:				Secs	RxKicks	TxKicks
 1G TCP Guest->Host:		3.94	  4686	  32815
 1M normal pings:		104	142862	1000010
 1M 1k pings (-l 120):		57	142026	1000007

After:
 1G TCP Guest->Host:		3.76	  4691	  32811
 1M normal pings:		111	142859	 997467
 1M 1k pings (-l 120):		55	 19648	 501549
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Rather than triggering an interrupt every time, we only trigger an
interrupt when there are no more incoming packets (or the recv queue
is full).

However, the overhead of doing the select to figure this out is
measurable: 1M pings goes from 98 to 104 seconds, and 1G Guest->Host
TCP goes from 3.69 to 3.94 seconds.  It's close to the noise though.

I tested various timeouts, including reducing it as the number of
pending packets increased, timing a 1 gigabyte TCP send from Guest ->
Host and Host -> Guest (GSO disabled, to increase packet rate).

// time tcpblast -o -s 65536 -c 16k 192.168.2.1:9999 > /dev/null

Timeout		Guest->Host	Pkts/irq	Host->Guest	Pkts/irq
Before		11.3s		1.0		6.3s		1.0
0		11.7s		1.0		6.6s		23.5
1		17.1s		8.8		8.6s		26.0
1/pending	13.4s		1.9		6.6s		23.8
2/pending	13.6s		2.8		6.6s		24.1
5/pending	14.1s		5.0		6.6s		24.4
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

If we track how many buffers we've used, we can tell whether we really
need to interrupt the Guest.  This happens as a side effect of
spurious notifications.

Spurious notifications happen because it can take a while before the
Host thread wakes up and sets the VRING_USED_F_NO_NOTIFY flag, and
meanwhile the Guest can more notifications.

A real fix would be to use wake counts, rather than a suppression
flag, but the practical difference is generally in the noise: the
interrupt is usually coalesced into a pending one anyway so we just
save a system call which isn't clearly measurable.

				Secs	Spurious IRQS
1G TCP Guest->Host:		3.93	58
1M normal pings:		100	72
1M 1k pings (-l 120):		57	492904
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Rather than sending an interrupt on every buffer, we only send an interrupt
when we're about to wait for the Guest to send us a new one.  The console
input and network input still send interrupts manually, but the block device,
network and console output queues can simply rely on this logic to send
interrupts to the Guest at the right time.

The patch is cluttered by moving trigger_irq() higher in the code.

In practice, two factors make this optimization less interesting:
(1) we often only get one input at a time, even for networking,
(2) triggering an interrupt rapidly tends to get coalesced anyway.

Before:				Secs	RxIRQS	TxIRQs
 1G TCP Guest->Host:		3.72	32784	32771
 1M normal pings:		99	1000004	995541
 100,000 1k pings (-l 120):	5	49510	49058

After:
 1G TCP Guest->Host:		3.69	32809	32769
 1M normal pings:		99	1000004	996196
 100,000 1k pings (-l 120):	5	52435	52361

(Note the interrupt count on 100k pings goes *up*: see next patch).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

We no longer need an efficient mechanism to force the Guest back into
host userspace, as each device is serviced without bothering the main
Guest process (aka. the Launcher).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Currently lguest has three threads: the main Launcher thread, a Waker
thread, and a thread for the block device (because synchronous block
was simply too painful to bear).

The Waker selects() on all the input file descriptors (eg. stdin, net
devices, pipe to the block thread) and when one becomes readable it calls
into the kernel to kick the Launcher thread out into userspace, which
repeats the poll, services the device(s), and then tells the kernel to
release the Waker before re-entering the kernel to run the Guest.

Also, to make a slightly-decent network transmit routine, the Launcher
would suppress further network interrupts while it set a timer: that
signal handler would write to a pipe, which would rouse the Waker
which would prod the Launcher out of the kernel to check the network
device again.

Now we can convert all our virtqueues to separate threads: each one has
a separate eventfd for when the Guest pokes the device, and can trigger
interrupts in the Guest directly.

The linecount shows how much this simplifies, but to really bring it
home, here's an strace analysis of single Guest->Host ping before:

* Guest sends packet, notifies xmit vq, return control to Launcher
* Launcher clears notification flag on xmit ring
* Launcher writes packet to TUN device
	writev(4, [{"\0\0\0\0\0\0\0\0\0\0", 10}, {"\366\r\224`\2058\272m\224vf\274\10\0E\0\0T\0\0@\0@\1\265"..., 98}], 2) = 108
* Launcher sets up interrupt for Guest (xmit ring is empty)
	write(10, "\2\0\0\0\3\0\0\0", 8) = 0
* Launcher sets up timer for interrupt mitigation
	setitimer(ITIMER_REAL, {it_interval={0, 0}, it_value={0, 505}}, NULL) = 0
* Launcher re-runs guest
	pread64(10, 0xbfa5f4d4, 4, 0) ...
* Waker notices reply packet in tun device (it was in select)
	select(12, [0 3 4 6 11], NULL, NULL, NULL) = 1 (in [4])
* Waker kicks Launcher out of guest:
	pwrite64(10, "\3\0\0\0\1\0\0\0", 8, 0) = 0
* Launcher returns from running guest:
	... = -1 EAGAIN (Resource temporarily unavailable)
* Launcher looks at input fds:
	select(7, [0 3 4 6], NULL, NULL, {0, 0}) = 1 (in [4], left {0, 0})
* Launcher reads pong from tun device:
	readv(4, [{"\0\0\0\0\0\0\0\0\0\0", 10}, {"\272m\224vf\274\366\r\224`\2058\10\0E\0\0T\364\26\0\0@"..., 1518}], 2) = 108
* Launcher injects guest notification:
	write(10, "\2\0\0\0\2\0\0\0", 8) = 0
* Launcher rechecks fds:
	select(7, [0 3 4 6], NULL, NULL, {0, 0}) = 0 (Timeout)
* Launcher clears Waker:
	pwrite64(10, "\3\0\0\0\0\0\0\0", 8, 0) = 0
* Launcher reruns Guest:
	pread64(10, 0xbfa5f4d4, 4, 0) = ? ERESTARTSYS (To be restarted)
* Signal comes in, uses pipe to wake up Launcher:
	--- SIGALRM (Alarm clock) @ 0 (0) ---
	write(8, "\0", 1)       = 1
	sigreturn()             = ? (mask now [])
* Waker sees write on pipe:
	select(12, [0 3 4 6 11], NULL, NULL, NULL) = 1 (in [6])
* Waker kicks Launcher out of Guest:
	pwrite64(10, "\3\0\0\0\1\0\0\0", 8, 0) = 0
* Launcher exits from kernel:
	pread64(10, 0xbfa5f4d4, 4, 0) = -1 EAGAIN (Resource temporarily unavailable)
* Launcher looks to see what fd woke it:
	select(7, [0 3 4 6], NULL, NULL, {0, 0}) = 1 (in [6], left {0, 0})
* Launcher reads timeout fd, sets notification flag on xmit ring
	read(6, "\0", 32)       = 1
* Launcher rechecks fds:
	select(7, [0 3 4 6], NULL, NULL, {0, 0}) = 0 (Timeout)
* Launcher clears Waker:
	pwrite64(10, "\3\0\0\0\0\0\0\0", 8, 0) = 0
* Launcher resumes Guest:
	pread64(10, "\0p\0\4", 4, 0) ....

strace analysis of single Guest->Host ping after:

* Guest sends packet, notifies xmit vq, creates event on eventfd.
* Network xmit thread wakes from read on eventfd:
	read(7, "\1\0\0\0\0\0\0\0", 8)          = 8
* Network xmit thread writes packet to TUN device
	writev(4, [{"\0\0\0\0\0\0\0\0\0\0", 10}, {"J\217\232FI\37j\27\375\276\0\304\10\0E\0\0T\0\0@\0@\1\265"..., 98}], 2) = 108
* Network recv thread wakes up from read on tunfd:
	readv(4, [{"\0\0\0\0\0\0\0\0\0\0", 10}, {"j\27\375\276\0\304J\217\232FI\37\10\0E\0\0TiO\0\0@\1\214"..., 1518}], 2) = 108
* Network recv thread sets up interrupt for the Guest
	write(6, "\2\0\0\0\2\0\0\0", 8) = 0
* Network recv thread goes back to reading tunfd
	13:39:42.460285 readv(4,  <unfinished ...>
* Network xmit thread sets up interrupt for Guest (xmit ring is empty)
	write(6, "\2\0\0\0\3\0\0\0", 8) = 0
* Network xmit thread goes back to reading from eventfd
	read(7, <unfinished ...>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>