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 <stefa...@redhat.com> --- 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 <stefa...@redhat.com> + * + * 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 <stefa...@redhat.com> + * + * 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