event_notifier: add Win32 implementation

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
event_notifier: enable it to use pipes

This takes the eventfd emulation code from the main loop.  When the
EventNotifier is used for the main loop too, we need this compatibility
code.

Without CONFIG_EVENTFD, event_notifier_get_fd is only usable for the
"read" side of the notifier, for example to set a select() handler.

The return value of event_notifier_set changes to the cleaner 0/-errno.
No caller is actually checking the return value.

Reviewed-by: Anthony Liguori <anthony@codemonkey.ws>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: change qemu_aio_set_fd_handler to return void

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: provide platform-independent API

This adds to aio.c a platform-independent API based on EventNotifiers, that
can be used by both POSIX and Win32.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: introduce AioContext, move bottom halves there

Start introducing AioContext, which will let us remove globals from
aio.c/async.c, and introduce multiple I/O threads.

The bottom half functions now take an additional AioContext argument.
A bottom half is created with a specific AioContext that remains the
same throughout the lifetime.  qemu_bh_new is just a wrapper that
uses a global context.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: add I/O handlers to the AioContext interface

With this patch, I/O handlers (including event notifier handlers) can be
attached to a single AioContext.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: test node->deleted before calling io_flush

Otherwise, there could be a case where io_flush accesses freed
memory because it should not have been called.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: add non-blocking variant of aio_wait

This will be used when polling the GSource attached to an AioContext.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: prepare for introducing GSource-based dispatch

This adds a GPollFD to each AioHandler.  It will then be possible to
attach these GPollFDs to a GSource, and from there to the main loop.
aio_wait examines the GPollFDs and avoids calling select() if any
is set (similar to what it does if bottom halves are available).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: add Win32 implementation

The Win32 implementation will only accept EventNotifiers, thus a few
drivers are disabled under Windows.  EventNotifiers are a good match
for the GSource implementation, too, because the Win32 port of glib
allows to place their HANDLEs in a GPollFD.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: make AioContexts GSources

This lets AioContexts be used (optionally) with a glib main loop.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: add aio_notify

With this change async.c does not rely anymore on any service from
main-loop.c, i.e. it is completely self-contained.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: call aio_notify after setting I/O handlers

In the current code, this is done by qemu_set_fd_handler2, which is
called by qemu_aio_set_fd_handler.  We need to keep the same behavior
even after removing the call to qemu_set_fd_handler2.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
main-loop: use GSource to poll AIO file descriptors

This lets us remove the hooks for the main loop in async.c.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
main-loop: use aio_notify for qemu_notify_event

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: clean up now-unused functions

Some cleanups can now be made, now that the main loop does not anymore need
hooks into the bottom half code.

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
linux-aio: use event notifiers

Since linux-aio already uses an eventfd, converting it to use the
EventNotifier-based API simplifies the code even though it is not
meant to be portable.

Reviewed-by: Anthony Liguori <anthony@codemonkey.ws>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
qemu-thread: add QemuSemaphore

The new thread pool will use semaphores instead of condition
variables, because QemuCond does not have qemu_cond_timedwait.
(I also like it more this way).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aio: add generic thread-pool facility

Add a generic thread-pool.  The code is roughly based on posix-aio-compat.c,
with some changes, especially the following:

- use QemuSemaphore instead of QemuCond;

- separate the state of the thread from the return code of the worker
function.  The return code is totally opaque for the thread pool;

- do not busy wait when doing cancellation.

A more generic threadpool (but still specific to I/O so that in the future
it can use special scheduling classes or PI mutexes) can have many uses:
it allows more flexibility in raw-posix.c and can more easily be extended
to Win32, and it will also be used to do an msync of the persistent bitmap.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
block: switch posix-aio-compat to threadpool

This is not meant for portability, but to remove code duplication.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>