Re: [Qemu-devel] [PATCH 7/9] iohandler: associate with main event loop via a QSource

[Paolo Bonzini]

Il 03/05/2013 18:03, Michael Roth ha scritto:
> This introduces a GlibQContext wrapper around the main GMainContext
> event loop, and associates iohandlers with it via a QSource (which
> GlibQContext creates a GSource from so that it can be driven via
> GLib. A subsequent patch will drive the GlibQContext directly)
> 
> We also add "QContext-aware" functionality to iohandler interfaces
> so that they can be bound to other QContext event loops, and add
> non-global set_fd_handler() interfaces to facilitate this. This is made
> possible by simply searching a given QContext for a QSource by the name
> of "iohandler" so that we can attach event handlers to the associated
> IOHandlerState.
> 
> Signed-off-by: Michael Roth <address@hidden>

This patch is why I think that this is a bit overengineered.  The main
loop is always glib-based, there should be no need to go through the
QSource abstraction.

BTW, this is broken for Win32.  The right thing to do here is to first
convert iohandler to a GSource in such a way that it works for both
POSIX and Win32, and then (if needed) we can later convert GSource to
QSource.

Paolo

> ---
>  include/qemu/main-loop.h |   31 +++++-
>  iohandler.c              |  238 
> ++++++++++++++++++++++++++++++++--------------
>  main-loop.c              |   21 +++-
>  3 files changed, 213 insertions(+), 77 deletions(-)
> 
> diff --git a/include/qemu/main-loop.h b/include/qemu/main-loop.h
> index 6f0200a..dbadf9f 100644
> --- a/include/qemu/main-loop.h
> +++ b/include/qemu/main-loop.h
> @@ -26,6 +26,7 @@
>  #define QEMU_MAIN_LOOP_H 1
>  
>  #include "block/aio.h"
> +#include "qcontext/qcontext.h"
>  
>  #define SIG_IPI SIGUSR1
>  
> @@ -168,9 +169,24 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc 
> *func, void *opaque);
>  
>  /* async I/O support */
>  
> +#define QSOURCE_IOHANDLER "iohandler"
> +
>  typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
>  typedef int IOCanReadHandler(void *opaque);
>  
> +QContext *qemu_get_qcontext(void);
> +/**
> + * iohandler_attach: Attach a QSource to a QContext
> + *
> + * This enables the use of IOHandler interfaces such as
> + * set_fd_handler() on the given QContext. IOHandler lists will be
> + * tracked/handled/dispatched based on a named QSource that is added to
> + * the QContext
> + *
> + * @ctx: A QContext to add an IOHandler QSource to
> + */
> +void iohandler_attach(QContext *ctx);
> +
>  /**
>   * qemu_set_fd_handler2: Register a file descriptor with the main loop
>   *
> @@ -217,6 +233,13 @@ int qemu_set_fd_handler2(int fd,
>                           IOHandler *fd_write,
>                           void *opaque);
>  
> +int set_fd_handler2(QContext *ctx,
> +                    int fd,
> +                    IOCanReadHandler *fd_read_poll,
> +                    IOHandler *fd_read,
> +                    IOHandler *fd_write,
> +                    void *opaque);
> +
>  /**
>   * qemu_set_fd_handler: Register a file descriptor with the main loop
>   *
> @@ -250,6 +273,12 @@ int qemu_set_fd_handler(int fd,
>                          IOHandler *fd_write,
>                          void *opaque);
>  
> +int set_fd_handler(QContext *ctx,
> +                   int fd,
> +                   IOHandler *fd_read,
> +                   IOHandler *fd_write,
> +                   void *opaque);
> +
>  #ifdef CONFIG_POSIX
>  /**
>   * qemu_add_child_watch: Register a child process for reaping.
> @@ -302,8 +331,6 @@ void qemu_mutex_unlock_iothread(void);
>  /* internal interfaces */
>  
>  void qemu_fd_register(int fd);
> -void qemu_iohandler_fill(GArray *pollfds);
> -void qemu_iohandler_poll(GArray *pollfds, int rc);
>  
>  QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
>  void qemu_bh_schedule_idle(QEMUBH *bh);
> diff --git a/iohandler.c b/iohandler.c
> index ae2ef8f..8625272 100644
> --- a/iohandler.c
> +++ b/iohandler.c
> @@ -41,38 +41,170 @@ typedef struct IOHandlerRecord {
>      int fd;
>      int pollfds_idx;
>      bool deleted;
> +    GPollFD pfd;
> +    bool pfd_added;
>  } IOHandlerRecord;
>  
> -static QLIST_HEAD(, IOHandlerRecord) io_handlers =
> -    QLIST_HEAD_INITIALIZER(io_handlers);
> +typedef struct IOHandlerState {
> +    QLIST_HEAD(, IOHandlerRecord) io_handlers;
> +} IOHandlerState;
>  
> +static bool iohandler_prepare(QSource *qsource, int *timeout)
> +{
> +    QSourceClass *qsourcek = QSOURCE_GET_CLASS(qsource);
> +    IOHandlerState *s = qsourcek->get_user_data(qsource);
> +    IOHandlerRecord *ioh;
>  
> -/* XXX: fd_read_poll should be suppressed, but an API change is
> -   necessary in the character devices to suppress fd_can_read(). */
> -int qemu_set_fd_handler2(int fd,
> -                         IOCanReadHandler *fd_read_poll,
> -                         IOHandler *fd_read,
> -                         IOHandler *fd_write,
> -                         void *opaque)
> +    QLIST_FOREACH(ioh, &s->io_handlers, next) {
> +        int events = 0;
> +
> +        if (ioh->deleted)
> +            continue;
> +
> +        if (ioh->fd_read &&
> +            (!ioh->fd_read_poll ||
> +             ioh->fd_read_poll(ioh->opaque) != 0)) {
> +            events |= G_IO_IN | G_IO_HUP | G_IO_ERR;
> +        }
> +        if (ioh->fd_write) {
> +            events |= G_IO_OUT | G_IO_ERR;
> +        }
> +        if (events) {
> +            ioh->pfd.fd = ioh->fd;
> +            ioh->pfd.events = events;
> +            if (!ioh->pfd_added) {
> +                qsourcek->add_poll(qsource, &ioh->pfd);
> +                ioh->pfd_added = true;
> +            }
> +        } else {
> +            ioh->pfd.events = 0;
> +            ioh->pfd.revents = 0;
> +        }
> +    }
> +    *timeout = 10;
> +    return false;
> +}
> +
> +static bool iohandler_check(QSource *qsource)
>  {
> +    QSourceClass *sourcek = QSOURCE_GET_CLASS(qsource);
> +    IOHandlerState *s = sourcek->get_user_data(qsource);
>      IOHandlerRecord *ioh;
>  
> +    QLIST_FOREACH(ioh, &s->io_handlers, next) {
> +        if (ioh->deleted) {
> +            continue;
> +        }
> +        if (ioh->pfd.revents) {
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +static bool iohandler_dispatch(QSource *qsource)
> +{
> +    QSourceClass *sourcek = QSOURCE_GET_CLASS(qsource);
> +    IOHandlerState *s = sourcek->get_user_data(qsource);
> +    IOHandlerRecord *pioh, *ioh;
> +
> +    QLIST_FOREACH_SAFE(ioh, &s->io_handlers, next, pioh) {
> +        int revents = ioh->pfd.revents;
> +        if (!ioh->deleted && ioh->fd_read &&
> +            (revents && (G_IO_IN | G_IO_HUP | G_IO_ERR))) {
> +            ioh->fd_read(ioh->opaque);
> +        }
> +
> +        if (!ioh->deleted && ioh->fd_write &&
> +            (revents & (G_IO_OUT | G_IO_ERR))) {
> +            ioh->fd_write(ioh->opaque);
> +        }
> +
> +        /* Do this last in case read/write handlers marked it for deletion */
> +        if (ioh->deleted) {
> +            if (ioh->pfd_added) {
> +                sourcek->remove_poll(qsource, &ioh->pfd);
> +            }
> +            QLIST_REMOVE(ioh, next);
> +            g_free(ioh);
> +        }
> +    }
> +
> +    return true;
> +}
> +
> +static void iohandler_finalize(QSource *qsource)
> +{
> +    QSourceClass *sourcek = QSOURCE_GET_CLASS(qsource);
> +    IOHandlerState *s = sourcek->get_user_data(qsource);
> +    IOHandlerRecord *pioh, *ioh;
> +
> +    QLIST_FOREACH_SAFE(ioh, &s->io_handlers, next, pioh) {
> +        if (ioh->pfd_added) {
> +            sourcek->remove_poll(qsource, &ioh->pfd);
> +        }
> +        QLIST_REMOVE(ioh, next);
> +        g_free(ioh);
> +    }
> +
> +    g_free(s);
> +}
> +
> +static const QSourceFuncs iohandler_funcs = {
> +    iohandler_prepare,
> +    iohandler_check,
> +    iohandler_dispatch,
> +    iohandler_finalize,
> +};
> +
> +void iohandler_attach(QContext *ctx)
> +{
> +    IOHandlerState *s;
> +    QSource *qsource;
> +
> +    s = g_new0(IOHandlerState, 1);
> +    QLIST_INIT(&s->io_handlers);
> +
> +    qsource = qsource_new(iohandler_funcs, NULL, QSOURCE_IOHANDLER, s);
> +    qcontext_attach(ctx, qsource, NULL);
> +}
> +
> +int set_fd_handler2(QContext *ctx,
> +                    int fd,
> +                    IOCanReadHandler *fd_read_poll,
> +                    IOHandler *fd_read,
> +                    IOHandler *fd_write,
> +                    void *opaque)
> +{
> +    QSourceClass *sourcek;
> +    QSource *source;
> +    IOHandlerState *s;
> +    IOHandlerRecord *ioh;
> +
> +    source = qcontext_find_source_by_name(ctx, QSOURCE_IOHANDLER);
> +    if (!source) {
> +        assert(0);
> +    }
> +    sourcek = QSOURCE_GET_CLASS(source);
> +    s = sourcek->get_user_data(source);
> +
>      assert(fd >= 0);
>  
>      if (!fd_read && !fd_write) {
> -        QLIST_FOREACH(ioh, &io_handlers, next) {
> +        QLIST_FOREACH(ioh, &s->io_handlers, next) {
>              if (ioh->fd == fd) {
>                  ioh->deleted = 1;
>                  break;
>              }
>          }
>      } else {
> -        QLIST_FOREACH(ioh, &io_handlers, next) {
> +        QLIST_FOREACH(ioh, &s->io_handlers, next) {
>              if (ioh->fd == fd)
>                  goto found;
>          }
>          ioh = g_malloc0(sizeof(IOHandlerRecord));
> -        QLIST_INSERT_HEAD(&io_handlers, ioh, next);
> +        QLIST_INSERT_HEAD(&s->io_handlers, ioh, next);
>      found:
>          ioh->fd = fd;
>          ioh->fd_read_poll = fd_read_poll;
> @@ -86,74 +218,34 @@ int qemu_set_fd_handler2(int fd,
>      return 0;
>  }
>  
> -int qemu_set_fd_handler(int fd,
> -                        IOHandler *fd_read,
> -                        IOHandler *fd_write,
> -                        void *opaque)
> +int set_fd_handler(QContext *ctx,
> +                   int fd,
> +                   IOHandler *fd_read,
> +                   IOHandler *fd_write,
> +                   void *opaque)
>  {
> -    return qemu_set_fd_handler2(fd, NULL, fd_read, fd_write, opaque);
> +    return set_fd_handler2(ctx, fd, NULL, fd_read, fd_write, opaque);
>  }
>  
> -void qemu_iohandler_fill(GArray *pollfds)
> +/* XXX: fd_read_poll should be suppressed, but an API change is
> +   necessary in the character devices to suppress fd_can_read(). */
> +int qemu_set_fd_handler2(int fd,
> +                         IOCanReadHandler *fd_read_poll,
> +                         IOHandler *fd_read,
> +                         IOHandler *fd_write,
> +                         void *opaque)
>  {
> -    IOHandlerRecord *ioh;
> -
> -    QLIST_FOREACH(ioh, &io_handlers, next) {
> -        int events = 0;
> -
> -        if (ioh->deleted)
> -            continue;
> -        if (ioh->fd_read &&
> -            (!ioh->fd_read_poll ||
> -             ioh->fd_read_poll(ioh->opaque) != 0)) {
> -            events |= G_IO_IN | G_IO_HUP | G_IO_ERR;
> -        }
> -        if (ioh->fd_write) {
> -            events |= G_IO_OUT | G_IO_ERR;
> -        }
> -        if (events) {
> -            GPollFD pfd = {
> -                .fd = ioh->fd,
> -                .events = events,
> -            };
> -            ioh->pollfds_idx = pollfds->len;
> -            g_array_append_val(pollfds, pfd);
> -        } else {
> -            ioh->pollfds_idx = -1;
> -        }
> -    }
> +    return set_fd_handler2(qemu_get_qcontext(), fd,
> +                           fd_read_poll, fd_read, fd_write,
> +                           opaque);
>  }
>  
> -void qemu_iohandler_poll(GArray *pollfds, int ret)
> +int qemu_set_fd_handler(int fd,
> +                        IOHandler *fd_read,
> +                        IOHandler *fd_write,
> +                        void *opaque)
>  {
> -    if (ret > 0) {
> -        IOHandlerRecord *pioh, *ioh;
> -
> -        QLIST_FOREACH_SAFE(ioh, &io_handlers, next, pioh) {
> -            int revents = 0;
> -
> -            if (!ioh->deleted && ioh->pollfds_idx != -1) {
> -                GPollFD *pfd = &g_array_index(pollfds, GPollFD,
> -                                              ioh->pollfds_idx);
> -                revents = pfd->revents;
> -            }
> -
> -            if (!ioh->deleted && ioh->fd_read &&
> -                (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR))) {
> -                ioh->fd_read(ioh->opaque);
> -            }
> -            if (!ioh->deleted && ioh->fd_write &&
> -                (revents & (G_IO_OUT | G_IO_ERR))) {
> -                ioh->fd_write(ioh->opaque);
> -            }
> -
> -            /* Do this last in case read/write handlers marked it for 
> deletion */
> -            if (ioh->deleted) {
> -                QLIST_REMOVE(ioh, next);
> -                g_free(ioh);
> -            }
> -        }
> -    }
> +    return qemu_set_fd_handler2(fd, NULL, fd_read, fd_write, opaque);
>  }
>  
>  /* reaping of zombies.  right now we're not passing the status to
> diff --git a/main-loop.c b/main-loop.c
> index f46aece..ae284a6 100644
> --- a/main-loop.c
> +++ b/main-loop.c
> @@ -27,6 +27,8 @@
>  #include "slirp/slirp.h"
>  #include "qemu/main-loop.h"
>  #include "block/aio.h"
> +#include "qcontext/qcontext.h"
> +#include "qcontext/glib-qcontext.h"
>  
>  #ifndef _WIN32
>  
> @@ -107,6 +109,13 @@ static int qemu_signal_init(void)
>  }
>  #endif
>  
> +static QContext *qemu_qcontext;
> +
> +QContext *qemu_get_qcontext(void)
> +{
> +    return qemu_qcontext;
> +}
> +
>  static AioContext *qemu_aio_context;
>  
>  AioContext *qemu_get_aio_context(void)
> @@ -128,6 +137,7 @@ int qemu_init_main_loop(void)
>  {
>      int ret;
>      GSource *src;
> +    Error *err = NULL;
>  
>      init_clocks();
>      if (init_timer_alarm() < 0) {
> @@ -135,6 +145,15 @@ int qemu_init_main_loop(void)
>          exit(1);
>      }
>  
> +    qemu_qcontext = QCONTEXT(glib_qcontext_new("main", false, &err));
> +    if (err) {
> +        g_warning("error initializing main qcontext");
> +        error_free(err);
> +        return -1;
> +    }
> +
> +    iohandler_attach(qemu_qcontext);
> +
>      ret = qemu_signal_init();
>      if (ret) {
>          return ret;
> @@ -464,9 +483,7 @@ int main_loop_wait(int nonblocking)
>      slirp_update_timeout(&timeout);
>      slirp_pollfds_fill(gpollfds);
>  #endif
> -    qemu_iohandler_fill(gpollfds);
>      ret = os_host_main_loop_wait(timeout);
> -    qemu_iohandler_poll(gpollfds, ret);
>  #ifdef CONFIG_SLIRP
>      slirp_pollfds_poll(gpollfds, (ret < 0));
>  #endif
>