[Qemu-devel] [RFC] Convert AioContext to Gsource sub classes

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

Hi folks,
  I'd like form a series which remove AioContext's concept and
bind to glib's main loop more closely. Since changed place will be
a bit much so want to know your opinion before real coding:

changes:
**before patch:
typedef struct AioContext {
    GSource source;
    int walking_handlers;
    QemuMutex bh_lock;
    struct QEMUBH *first_bh;
    int walking_bh;
    EventNotifier notifier;
    GArray *pollfds;
    struct ThreadPool *thread_pool;
} AioContext;

**After patch:
typedef struct BhSource {
    GSource source;
    QemuMutex bh_lock;
    struct QEMUBH *first_bh;
    int walking_bh;
} BhSource;

typedef struct FdSource {
    GSource source;
    int walking_handlers;
    EventNotifier notifier;
    GArray *pollfds;
    struct ThreadPool *thread_pool;
} FdSource;

Benefits:
  Original code have a mix of Gsource and GMainContext's concept, we
may want to add wrapper functions around GMainContext's functions, such
as g_main_context_acquire(), g_main_context_prepare(), which brings
extra effort if you want to form a good and clear API layer. With
this changes, all qemu's custom code is attached under Gsource, we
have a clear GMainContext's API layer for event loop, no wrapper is
needed, and the event's loop API is glib's API, a clear layer let
me form a library or adding more things.

before:
qemu's mainloop caller,  BH user, fd user
                      |
                   AioContext
                      |
                GMainContext


after:
qemu's mainloop caller
    |                                   BH user    fd user
GmainContext                               |         |
    |--------------------------------|--BhSource     |
                                     |-------------FdSource


Note:
  FdSource could be split more into ThreadSource and FdSource, which
distinguish more. It can be done easily if the change of this series
is online, when found necessary.

  More reasons:
  When I thinking how to bind library code to a thread context, it may
need to add Context's concept into API of block.c. If I use AioContext,
there will need a wrapper API to run the event loop. But If I got
glib's GmainContext, things become simple.
-- 
Best Regards

Wenchao Xia