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

[Fam Zheng]

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.

Fam

>  tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(test-block-obj-y)
>  tests/test-aio$(EXESUF): tests/test-aio.o $(test-block-obj-y)
>  tests/test-aio-multithread$(EXESUF): tests/test-aio-multithread.o 
> $(test-block-obj-y)
> -- 
> 2.9.3
> 
>