aio / timers: Rename qemu_new_clock and expose clock types

Rename qemu_new_clock to qemu_clock_new.

Expose clock types.
aio / timers: add qemu-timer.c utility functions

Add utility functions to qemu-timer.c for nanosecond timing.

Add qemu_clock_deadline_ns to calculate deadlines to
nanosecond accuracy.

Add utility function qemu_soonest_timeout to calculate soonest deadline.

Add qemu_timeout_ns_to_ms to convert a timeout in nanoseconds back to
milliseconds for when ppoll is not used.

Signed-off-by: Alex Bligh <alex@alex.org.uk>
aio / timers: Consistent treatment of disabled clocks for deadlines

Make treatment of disabled clocks consistent in deadline calculation

Signed-off-by: Alex Bligh <alex@alex.org.uk>
aio / timers: add ppoll support with qemu_poll_ns

Add qemu_poll_ns which works like g_poll but takes a nanosecond
timeout.
aio / timers: Add prctl(PR_SET_TIMERSLACK, 1, ...) to reduce timer slack

Where supported, called prctl(PR_SET_TIMERSLACK, 1, ...) to
set one nanosecond timer slack to increase precision of timer
calls.
aio / timers: Make qemu_run_timers and qemu_run_all_timers return progress

Make qemu_run_timers and qemu_run_all_timers return progress
so that aio_poll etc. can determine whether a timer has been
run.
aio / timers: Split QEMUClock into QEMUClock and QEMUTimerList

Split QEMUClock into QEMUClock and QEMUTimerList so that we can
have more than one QEMUTimerList associated with the same clock.

Introduce a main_loop_timerlist concept and make existing
qemu_clock_* calls that actually should operate on a QEMUTimerList
call the relevant QEMUTimerList implementations, using the clock's
default timerlist. This vastly reduces the invasiveness of this
change and means the API stays constant for existing users.

Introduce a list of QEMUTimerLists associated with each clock
so that reenabling the clock can cause all the notifiers
to be called. Note the code to do the notifications is added
in a later patch.

Switch QEMUClockType to an enum. Remove global variables vm_clock,
host_clock and rt_clock and add compatibility defines. Do not
fix qemu_next_alarm_deadline as it's going to be deleted.

Add qemu_clock_use_for_deadline to indicate whether a particular
clock should be used for deadline calculations. When use_icount
is true, vm_clock should not be used for deadline calculations
as it does not contain a nanosecond count. Instead, icount
timeouts come from the execution thread doing aio_notify or
qemu_notify as appropriate. This function is used in the next
patch.
aio / timers: Untangle include files

include/qemu/timer.h has no need to include main-loop.h and
doing so causes an issue for the next patch. Unfortunately
various files assume including timers.h will pull in main-loop.h.
Untangle this mess.
aio / timers: Add QEMUTimerListGroup and helper functions

Add QEMUTimerListGroup and helper functions, to represent
a QEMUTimerList associated with each clock. Add a default
QEMUTimerListGroup representing the default timer lists
which are not associated with any other object (e.g.
an AioContext as added by future patches).
aio / timers: Add QEMUTimerListGroup to AioContext

Add a QEMUTimerListGroup each AioContext (meaning a QEMUTimerList
associated with each clock is added) and delete it when the
AioContext is freed.
aio / timers: Add a notify callback to QEMUTimerList

Add a notify pointer to QEMUTimerList so it knows what to notify
on a timer change.
aio / timers: aio_ctx_prepare sets timeout from AioContext timers

Calculate the timeout in aio_ctx_prepare taking into account
the timers attached to the AioContext.

Alter aio_ctx_check similarly.
aio / timers: Add aio_timer_new wrapper

Add aio_timer_new wrapper function.
aio / timers: Convert aio_poll to use AioContext timers' deadline

Convert aio_poll to use deadline based on AioContext's timers.

aio_poll has been changed to return accurately whether progress
has occurred. Prior to this commit, aio_poll always returned
true if g_poll was entered, whether or not any progress was
made. This required a change to tests/test-aio.c where an
assert was backwards.
aio / timers: Convert mainloop to use timeout

Convert mainloop to use timeout from default timerlist group
(i.e. the current 3 static timers)
aio / timers: On timer modification, qemu_notify or aio_notify

On qemu_mod_timer_ns, ensure qemu_notify or aio_notify is called to
end the appropriate poll(), irrespective of use_icount value.

On qemu_clock_enable, ensure qemu_notify or aio_notify is called for
all QEMUTimerLists attached to the QEMUClock.
aio / timers: Introduce new API qemu_timer_new and friends

Introduce new API for creating timers - qemu_timer_new and
_ns, _ms, _us derivatives.
aio / timers: Use all timerlists in icount warp calculations

Notify all timerlists derived from vm_clock in icount warp
calculations.

When calculating timer delay based on vm_clock deadline, use
all timerlists.

For compatibility, maintain an apparent bug where when using
icount, if no vm_clock timer was set, qemu_clock_deadline
would return INT32_MAX and always set an icount clock expiry
about 2 seconds ahead.

NB: thread safety - when different timerlists sit on different
threads, this will need some locking.
aio / timers: Add documentation and new format calls

Add documentation for existing qemu timer calls. Add new format
calls of the format qemu_timer_XXX rather than qemu_XXX_timer
for consistency.
aio / timers: Remove alarm timers

Remove alarm timers from qemu-timers.c now we use g_poll / ppoll
instead.