Re: [Qemu-devel] [PATCH 02/11] poller: add Poller for growable GPollFD arrays

[Anthony Liguori]

Stefan Hajnoczi <address@hidden> writes:

> QEMU currently uses select(2)-style rfds/wfds/xfds for file descriptor
> event polling.  Unfortunately the underlying fd_set type and its macros
> (FD_SET()) have a hardcoded maximum for file descriptors.  It is
> possible to exceed this limit so we need a more scalable event polling
> structure.
>
> Poller is a growable array of GPollFDs that will allow us to use
> g_poll(3) instead of select(2) in the future.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>

How about using a GArray instead?

Regards,

Anthony Liguori

> ---
>  include/qemu/poller.h | 56 
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  util/Makefile.objs    |  1 +
>  util/poller.c         | 54 +++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 111 insertions(+)
>  create mode 100644 include/qemu/poller.h
>  create mode 100644 util/poller.c
>
> diff --git a/include/qemu/poller.h b/include/qemu/poller.h
> new file mode 100644
> index 0000000..7630099
> --- /dev/null
> +++ b/include/qemu/poller.h
> @@ -0,0 +1,56 @@
> +/*
> + * Growable GPollFD arrays
> + *
> + * Copyright 2013 Red Hat, Inc. and/or its affiliates
> + *
> + * Authors:
> + *   Stefan Hajnoczi    <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2 or later.
> + * See the COPYING.LIB file in the top-level directory.
> + *
> + */
> +
> +#ifndef QEMU_POLLER_H
> +#define QEMU_POLLER_H
> +
> +#include "qemu-common.h"
> +
> +typedef struct {
> +    GPollFD *poll_fds;
> +    int nfds;
> +    int max;
> +} Poller;
> +
> +void poller_init(Poller *p);
> +void poller_cleanup(Poller *p);
> +
> +/**
> + * poller_reset: Forget all added file descriptors
> + */
> +void poller_reset(Poller *p);
> +
> +/**
> + * poller_add_fd: Enable event polling on a file descriptor
> + *
> + * Called by *_fill() functions that are invoked by the main loop to enable
> + * event polling on file descriptors that they care about.  The results can 
> be
> + * fetched with poller_get_revents() when the corresponding *_poll() function
> + * is invoked by the main loop.
> + *
> + * Return an index that can be used with poller_get_revents().
> + *
> + * @events: GIOCondition (G_IO_IN, G_IO_OUT, etc) bitmask
> + */
> +int poller_add_fd(Poller *p, int fd, int events);
> +
> +/**
> + * poller_get_revents: Fetch event polling results for an added file 
> descriptor
> + *
> + * Return the GIOCondition (G_IO_IN, G_IO_OUT, etc) bitmask.
> + *
> + * @index: Return value from poller_add_fd().  This is not an fd!
> + */
> +int poller_get_revents(Poller *p, int index);
> +
> +#endif /* QEMU_POLLER_H */
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index 495a178..7ff18d6 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -8,3 +8,4 @@ util-obj-y += error.o qemu-error.o
>  util-obj-$(CONFIG_POSIX) += compatfd.o
>  util-obj-y += iov.o aes.o qemu-config.o qemu-sockets.o uri.o notify.o
>  util-obj-y += qemu-option.o qemu-progress.o
> +util-obj-y += poller.o
> diff --git a/util/poller.c b/util/poller.c
> new file mode 100644
> index 0000000..663e7a9
> --- /dev/null
> +++ b/util/poller.c
> @@ -0,0 +1,54 @@
> +/*
> + * Growable GPollFD arrays
> + *
> + * Copyright 2013 Red Hat, Inc. and/or its affiliates
> + *
> + * Authors:
> + *   Stefan Hajnoczi    <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2 or later.
> + * See the COPYING.LIB file in the top-level directory.
> + *
> + */
> +
> +#include <assert.h>
> +#include <string.h>
> +#include "qemu/poller.h"
> +
> +void poller_init(Poller *p)
> +{
> +    memset(p, 0, sizeof(*p));
> +}
> +
> +void poller_cleanup(Poller *p)
> +{
> +    g_free(p->poll_fds);
> +}
> +
> +void poller_reset(Poller *p)
> +{
> +    p->nfds = 0;
> +}
> +
> +int poller_add_fd(Poller *p, int fd, int events)
> +{
> +    int index;
> +
> +    index = p->nfds++;
> +    if (index >= p->max) {
> +        p->max += 64; /* avoid constant reallocation */
> +        p->poll_fds = g_realloc(p->poll_fds, p->max * 
> sizeof(p->poll_fds[0]));
> +    }
> +
> +    p->poll_fds[index] = (GPollFD){
> +        .fd = fd,
> +        .events = events,
> +    };
> +    return index;
> +}
> +
> +int poller_get_revents(Poller *p, int index)
> +{
> +    assert(index < p->nfds);
> +    return p->poll_fds[index].revents;
> +}
> -- 
> 1.8.1