Re: [PATCH 4/4] coroutine: Break inclusion loop

[Paolo Bonzini]

dropped qemu-devel by mistake.

Paolo 

Il lun 12 dic 2022, 23:16 Paolo Bonzini <pbonzini@redhat.com> ha scritto:

On 12/8/22 15:23, Markus Armbruster wrote:
> qemu/coroutine.h and qemu/lockable.h include each other.  Neither
> header actually needs the other one.

qemu/lockable.h wants qemu/coroutine.h because of the reference to
qemu_co_mutex_lock/unlock in the QEMU_MAKE_LOCKABLE macro.  Said
reference only happens when the macro is used, so strictly speaking
only code that uses of qemu/lockable.h's functionality needs to
include qemu/coroutine.h.  The order doesn't matter.

qemu/coroutine.h similarly wants qemu/lockable.h only for a macro: it
uses QemuLockable for the prototype of qemu_co_queue_wait_impl, but
QemuLockable is defined in qemu/typedefs.h.  On the other hand, the
qemu_co_queue_wait macro needs QEMU_MAKE_LOCKABLE.  Again, the order
does not matter but callers of qemu_co_queue_wait appreciate it if
both files are included.

So, this is why the inclusion loop works.  This patch makes some
files include qemu/coroutine.h even if they only need qemu/lockable.h
for QEMU_LOCK_GUARD of a "regular" QemuMutex; for example, linux-user/
does not use coroutines, so I'd like to avoid that it includes
qemu/coroutine.h.

One way is to just keep the cycle.  Another is to break the cycle is
as follows:

1) qemu/coroutine.h keeps including qemu/lockable.h

2) qemu/lockable.h is modified as follows to omit the reference to CoMutex:

diff --git a/include/qemu/lockable.h b/include/qemu/lockable.h
index 86db7cb04c9c..db59656538a4 100644
--- a/include/qemu/lockable.h
+++ b/include/qemu/lockable.h
@@ -71,9 +71,11 @@ qemu_null_lockable(void *x)
               void *: qemu_null_lockable(x),                             \
               QemuMutex *: qemu_make_lockable(x, QML_OBJ_(x, mutex)),    \
               QemuRecMutex *: qemu_make_lockable(x, QML_OBJ_(x, rec_mutex)), \
-             CoMutex *: qemu_make_lockable(x, QML_OBJ_(x, co_mutex)),   \
+             QEMU_MAKE_CO_MUTEX_LOCKABLE(x)                             \
               QemuSpin *: qemu_make_lockable(x, QML_OBJ_(x, spin)))

+#define QEMU_MAKE_CO_MUTEX_LOCKABLE(x)
+
  /**
   * QEMU_MAKE_LOCKABLE_NONNULL - Make a polymorphic QemuLockable
   *

3) the following hack is added in qemu/coroutine.h, right after including qemu/lockable.h:

#undef QEMU_MAKE_CO_MUTEX_LOCKABLE(x)
#define QEMU_MAKE_CO_MUTEX_LOCKABLE(x) \
              CoMutex *: qemu_make_lockable(x, QML_OBJ_(x, co_mutex)),


Neither is particularly pretty, so I vote for leaving things as is with
a comment above the two #include directives.

Paolo