Re: [Qemu-devel] [PATCH 05/16] io: make qio_channel_yield aware of AioContexts

[Daniel P. Berrange]

On Mon, Jan 16, 2017 at 07:38:24PM +0800, Fam Zheng wrote:
> On Fri, 01/13 14:17, Paolo Bonzini wrote:
> > Support separate coroutines for reading and writing, and place the
> > read/write handlers on the AioContext that the QIOChannel is registered
> > with.
> > 
> > Signed-off-by: Paolo Bonzini <address@hidden>
> > ---
> >  include/io/channel.h   | 37 ++++++++++++++++++----
> >  io/channel.c           | 86 
> > ++++++++++++++++++++++++++++++++++++++------------
> >  tests/Makefile.include |  2 +-
> >  3 files changed, 96 insertions(+), 29 deletions(-)
> > 
> > diff --git a/include/io/channel.h b/include/io/channel.h
> > index 665edd7..d7bad94 100644
> > --- a/include/io/channel.h
> > +++ b/include/io/channel.h
> > @@ -23,6 +23,7 @@
> >  
> >  #include "qemu-common.h"
> >  #include "qom/object.h"
> > +#include "qemu/coroutine.h"
> >  #include "block/aio.h"
> >  
> >  #define TYPE_QIO_CHANNEL "qio-channel"
> > @@ -59,8 +60,6 @@ typedef gboolean (*QIOChannelFunc)(QIOChannel *ioc,
> >                                     GIOCondition condition,
> >                                     gpointer data);
> >  
> > -typedef struct QIOChannelRestart QIOChannelRestart;
> > -
> >  /**
> >   * QIOChannel:
> >   *
> > @@ -84,8 +83,8 @@ struct QIOChannel {
> >      unsigned int features; /* bitmask of QIOChannelFeatures */
> >      char *name;
> >      AioContext *ctx;
> > -    QIOChannelRestart *read_coroutine;
> > -    QIOChannelRestart *write_coroutine;
> > +    Coroutine *read_coroutine;
> > +    Coroutine *write_coroutine;
> >  #ifdef _WIN32
> >      HANDLE event; /* For use with GSource on Win32 */
> >  #endif
> > @@ -508,13 +507,37 @@ guint qio_channel_add_watch(QIOChannel *ioc,
> >  
> >  
> >  /**
> > + * qio_channel_set_aio_context:
> > + * @ioc: the channel object
> > + * @ctx: the #AioContext to set the handlers on
> > + *
> > + * Request that qio_channel_yield() sets I/O handlers on
> > + * the given #AioContext.  If @ctx is %NULL, qio_channel_yield()
> > + * uses QEMU's main thread event loop.
> > + */
> > +void qio_channel_set_aio_context(QIOChannel *ioc,
> > +                                 AioContext *ctx);
> > +
> > +/**
> > + * qio_channel_detach_aio_context:
> > + * @ioc: the channel object
> > + *
> > + * Disable any I/O handlers set by qio_channel_yield().  With the
> > + * help of aio_co_schedule(), this allows moving a coroutine that was
> > + * paused by qio_channel_yield() to another context.
> > + */
> > +void qio_channel_detach_aio_context(QIOChannel *ioc);
> > +
> > +/**
> >   * qio_channel_yield:
> >   * @ioc: the channel object
> >   * @condition: the I/O condition to wait for
> >   *
> > - * Yields execution from the current coroutine until
> > - * the condition indicated by @condition becomes
> > - * available.
> > + * Yields execution from the current coroutine until the condition
> > + * indicated by @condition becomes available.  @condition must
> > + * be either %G_IO_IN or %G_IO_OUT; it cannot contain both.  In
> > + * addition, no two coroutine can be waiting on the same condition
> > + * and channel at the same time.
> >   *
> >   * This must only be called from coroutine context
> >   */
> > diff --git a/io/channel.c b/io/channel.c
> > index ce470d7..1e043bf 100644
> > --- a/io/channel.c
> > +++ b/io/channel.c
> > @@ -21,7 +21,7 @@
> >  #include "qemu/osdep.h"
> >  #include "io/channel.h"
> >  #include "qapi/error.h"
> > -#include "qemu/coroutine.h"
> > +#include "qemu/main-loop.h"
> >  
> >  bool qio_channel_has_feature(QIOChannel *ioc,
> >                               QIOChannelFeature feature)
> > @@ -238,36 +238,80 @@ off_t qio_channel_io_seek(QIOChannel *ioc,
> >  }
> >  
> >  
> > -typedef struct QIOChannelYieldData QIOChannelYieldData;
> > -struct QIOChannelYieldData {
> > -    QIOChannel *ioc;
> > -    Coroutine *co;
> > -};
> > +static void qio_channel_set_aio_fd_handlers(QIOChannel *ioc);
> > +
> > +static void qio_channel_restart_read(void *opaque)
> > +{
> > +    QIOChannel *ioc = opaque;
> > +    Coroutine *co = ioc->read_coroutine;
> >  
> > +    ioc->read_coroutine = NULL;
> > +    qio_channel_set_aio_fd_handlers(ioc);
> > +    aio_co_wake(co);
> > +}
> >  
> > -static gboolean qio_channel_yield_enter(QIOChannel *ioc,
> > -                                        GIOCondition condition,
> > -                                        gpointer opaque)
> > +static void qio_channel_restart_write(void *opaque)
> >  {
> > -    QIOChannelYieldData *data = opaque;
> > -    qemu_coroutine_enter(data->co);
> > -    return FALSE;
> > +    QIOChannel *ioc = opaque;
> > +    Coroutine *co = ioc->write_coroutine;
> > +
> > +    ioc->write_coroutine = NULL;
> > +    qio_channel_set_aio_fd_handlers(ioc);
> > +    aio_co_wake(co);
> >  }
> >  
> > +static void qio_channel_set_aio_fd_handlers(QIOChannel *ioc)
> > +{
> > +    IOHandler *rd_handler = NULL, *wr_handler = NULL;
> > +    AioContext *ctx;
> > +
> > +    if (ioc->read_coroutine) {
> > +   rd_handler = qio_channel_restart_read;
> 
> s/\t/        /
> 
> > +    }
> > +    if (ioc->write_coroutine) {
> > +   rd_handler = qio_channel_restart_write;
> 
> s/\t/        /
> 
> > +    }
> > +
> > +    ctx = ioc->ctx ? ioc->ctx : iohandler_get_aio_context();
> > +    qio_channel_set_aio_fd_handler(ioc, ctx, rd_handler, wr_handler, ioc);
> > +}
> > +
> > +void qio_channel_set_aio_context(QIOChannel *ioc,
> > +                                 AioContext *ctx)
> > +{
> > +    AioContext *old_ctx;
> > +    if (ioc->ctx == ctx) {
> > +        return;
> > +    }
> > +
> > +    old_ctx = ioc->ctx ? ioc->ctx : iohandler_get_aio_context();
> > +    qio_channel_set_aio_fd_handler(ioc, old_ctx, NULL, NULL, NULL);
> > +    ioc->ctx = ctx;
> > +    qio_channel_set_aio_fd_handlers(ioc);
> > +}
> > +
> > +void qio_channel_detach_aio_context(QIOChannel *ioc)
> > +{
> > +    ioc->read_coroutine = NULL;
> > +    ioc->write_coroutine = NULL;
> > +    qio_channel_set_aio_fd_handlers(ioc);
> 
> Why is qio_channel_set_aio_fd_handler not needed here?
> 
> > +    ioc->ctx = NULL;
> > +}
> >  
> >  void coroutine_fn qio_channel_yield(QIOChannel *ioc,
> >                                      GIOCondition condition)
> >  {
> > -    QIOChannelYieldData data;
> > -
> >      assert(qemu_in_coroutine());
> > -    data.ioc = ioc;
> > -    data.co = qemu_coroutine_self();
> > -    qio_channel_add_watch(ioc,
> > -                          condition,
> > -                          qio_channel_yield_enter,
> > -                          &data,
> > -                          NULL);
> > +    if (condition == G_IO_IN) {
> > +        assert(!ioc->read_coroutine);
> > +        ioc->read_coroutine = qemu_coroutine_self();
> > +    } else if (condition == G_IO_OUT) {
> > +        assert(!ioc->write_coroutine);
> > +        ioc->write_coroutine = qemu_coroutine_self();
> > +    } else {
> > +        abort();
> > +    }
> > +    qio_channel_set_aio_fd_handlers(ioc);
> >      qemu_coroutine_yield();
> >  }
> >  
> > diff --git a/tests/Makefile.include b/tests/Makefile.include
> > index 3b8ed9d..7d11bbb 100644
> > --- a/tests/Makefile.include
> > +++ b/tests/Makefile.include
> > @@ -493,7 +493,7 @@ tests/check-qjson$(EXESUF): tests/check-qjson.o 
> > $(test-util-obj-y)
> >  tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o 
> > $(test-qom-obj-y)
> >  tests/check-qom-proplist$(EXESUF): tests/check-qom-proplist.o 
> > $(test-qom-obj-y)
> >  
> > -tests/test-char$(EXESUF): tests/test-char.o qemu-char.o qemu-timer.o 
> > $(test-util-obj-y) $(qtest-obj-y) $(test-io-obj-y)
> > +tests/test-char$(EXESUF): tests/test-char.o qemu-char.o qemu-timer.o 
> > $(test-util-obj-y) $(qtest-obj-y) $(test-io-obj-y) $(test-block-obj-y)
> 
> I guess this is a hint for moving coroutine code into a lower level library 
> like
> util.

The coroutine code is already in util/, so I'm assuming this is actually
for the AioContext stuff. Yes, though, AioContext ought to be moved into
util/ as part of this series IMHO, since the io/ channel code shouldn't
have a dependancy on block/ layer.

Regards,
Daniel
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