MFC r275698: MFV r275696: file 5.21.
MFC r267276:

  Ensure files are created during the build when using bsd.subdir.mk.

  When FILES is defined in a Makefile that _also_ includes bsd.subdir.mk, the
  build of the files (if any) was not properly triggered during the build
  stage.  This was because bsd.files.mk did not define the buildfiles target
  if it was already defined... and bsd.subdir.mk defined this target on its
  own, thus causing a conflict.

  Fix this by unconditionally defining buildfiles from bsd.files.mk; this is
  safe because nothing else in the tree needs to redefine this and because the
  target itself contains no commands: all it does is define dependencies.
  Also ensure that bsd.files.mk is always pulled in by bsd.test.mk regardless
  of what bsd.prog.mk does.

  These fixes allow "make installworld" to run cleanly on a system with
  read-only src and obj trees.

  This is "make tinderbox" clean.

  Reviewed by:	imp
  Obtained from:	jilles
MFC r274077:

  As an optimization (in simple, well used cases) only call cat ${.ALLSRC} when
  generating files from various sources instead of calling cat ${.ALLSRC} | sed

  The perl case was skipped because it's not being used in the tree at this time
MFC r273683
Move the ACPI PM timer emulation into vmm.ko.

MFC r273706
Change the type of the first argument to the I/O emulation handlers to
'struct vm *'.

MFC r273710
Add a comment explaining the intent behind the I/O reservation [0x72-0x77].

MFC r273744
Add foo_genassym.c files to DPSRCS so dependencies for them are generated.
This ensures these objects are rebuilt to generate an updated header of
assembly constants if needed.

MFC r274045
If the start bit, PxCMD.ST, is cleared and nothing is in-flight then
PxCI, PxSACT, PxCMD.CCS and PxCMD.CR should be 0.

MFC r274076
Improve the ability to cancel an in-flight request by using an interrupt,
via SIGCONT, to force the read or write system call to return prematurely.

MFC r274330
To allow a request to be submitted from within the callback routine of
a completing one increase the total by 1 but don't advertise it.

MFC r274931
Change the lower bound for guest vmspace allocation to 0 instead of using
the VM_MIN_ADDRESS constant.

MFC r275817
For level triggered interrupts clear the PIC IRR bit when the interrupt pin
is deasserted.

MFC r275850
Fix 8259 IRQ priority resolver.

MFC r275952
Various 8259 device model improvements.

MFC r275965
Emulate writes to the IA32_MISC_ENABLE MSR.
MFH r274083:
convert .Nm to proper .Xr's...

MFH r275298:
Cross reference tap(4) and tun(4) and include a short explanation as
to how they differ.  This will assist users in selecting which interface
is more appropriate for their purposes.

No objection:	jmg (r274083)
Approved by:	grog (co-mentor)
MFC: r276192, r276200
Modify vop_stdadvlock{async}() so that it only
locks/unlocks the vnode and does a VOP_GETATTR()
for the SEEK_END case. This is safe to do, since
lf_advlock{async}() only uses the size argument
for the SEEK_END case.
The NFSv4 server needs this when
vfs.nfsd.enable_locallocks!=0 since locking the
vnode results in a LOR that can cause a deadlock
for the nfsd threads.
MFC: r276193
A deadlock in the NFSv4 server with vfs.nfsd.enable_locallocks=1
was reported via email. This was caused by a LOR between the
sleep lock used to serialize the local locking (nfsrv_locklf())
and locking the vnode. I believe this patch fixes the problem
by delaying relocking of the vnode until the sleep lock is
unlocked (nfsrv_unlocklf()). To avoid nfsvno_advlock() having the side
effect of unlocking the vnode, unlocking the vnode was moved to before
the functions that call nfsvno_advlock().
It shouldn't affect the execution of the default case where
vfs.nfsd.enable_locallocks=0.
MFC: r276221
Delete some duplicate code that was harmless because
exactly the same code is at the end of the nfscl_checksattr()
function that is called just before it. As such, this code
had already been executed and didn't do anything.