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

[Stefan Hajnoczi]

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>
---
 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