1 files changed, 151 insertions, 0 deletions
diff --git a/util/fdmon-epoll.c b/util/fdmon-epoll.c
new file mode 100644
index 0000000000..29c1454469
--- /dev/null
+++ b/util/fdmon-epoll.c
@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * epoll(7) file descriptor monitoring
+ */
+
+#include "qemu/osdep.h"
+#include <sys/epoll.h>
+#include "qemu/rcu_queue.h"
+#include "aio-posix.h"
+
+/* The fd number threshold to switch to epoll */
+#define EPOLL_ENABLE_THRESHOLD 64
+
+void fdmon_epoll_disable(AioContext *ctx)
+{
+    if (ctx->epollfd >= 0) {
+        close(ctx->epollfd);
+        ctx->epollfd = -1;
+    }
+
+    /* Switch back */
+    ctx->fdmon_ops = &fdmon_poll_ops;
+}
+
+static inline int epoll_events_from_pfd(int pfd_events)
+{
+    return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
+           (pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
+           (pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
+           (pfd_events & G_IO_ERR ? EPOLLERR : 0);
+}
+
+static void fdmon_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
+{
+    struct epoll_event event;
+    int r;
+    int ctl;
+
+    if (!node->pfd.events) {
+        ctl = EPOLL_CTL_DEL;
+    } else {
+        event.data.ptr = node;
+        event.events = epoll_events_from_pfd(node->pfd.events);
+        ctl = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
+    }
+
+    r = epoll_ctl(ctx->epollfd, ctl, node->pfd.fd, &event);
+    if (r) {
+        fdmon_epoll_disable(ctx);
+    }
+}
+
+static int fdmon_epoll_wait(AioContext *ctx, AioHandlerList *ready_list,
+                            int64_t timeout)
+{
+    GPollFD pfd = {
+        .fd = ctx->epollfd,
+        .events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR,
+    };
+    AioHandler *node;
+    int i, ret = 0;
+    struct epoll_event events[128];
+
+    /* Fall back while external clients are disabled */
+    if (atomic_read(&ctx->external_disable_cnt)) {
+        return fdmon_poll_ops.wait(ctx, ready_list, timeout);
+    }
+
+    if (timeout > 0) {
+        ret = qemu_poll_ns(&pfd, 1, timeout);
+        if (ret > 0) {
+            timeout = 0;
+        }
+    }
+    if (timeout <= 0 || ret > 0) {
+        ret = epoll_wait(ctx->epollfd, events,
+                         ARRAY_SIZE(events),
+                         timeout);
+        if (ret <= 0) {
+            goto out;
+        }
+        for (i = 0; i < ret; i++) {
+            int ev = events[i].events;
+            int revents = (ev & EPOLLIN ? G_IO_IN : 0) |
+                          (ev & EPOLLOUT ? G_IO_OUT : 0) |
+                          (ev & EPOLLHUP ? G_IO_HUP : 0) |
+                          (ev & EPOLLERR ? G_IO_ERR : 0);
+
+            node = events[i].data.ptr;
+            aio_add_ready_handler(ready_list, node, revents);
+        }
+    }
+out:
+    return ret;
+}
+
+static const FDMonOps fdmon_epoll_ops = {
+    .update = fdmon_epoll_update,
+    .wait = fdmon_epoll_wait,
+};
+
+static bool fdmon_epoll_try_enable(AioContext *ctx)
+{
+    AioHandler *node;
+    struct epoll_event event;
+
+    QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+        int r;
+        if (QLIST_IS_INSERTED(node, node_deleted) || !node->pfd.events) {
+            continue;
+        }
+        event.events = epoll_events_from_pfd(node->pfd.events);
+        event.data.ptr = node;
+        r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
+        if (r) {
+            return false;
+        }
+    }
+
+    ctx->fdmon_ops = &fdmon_epoll_ops;
+    return true;
+}
+
+bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
+{
+    if (ctx->epollfd < 0) {
+        return false;
+    }
+
+    /* Do not upgrade while external clients are disabled */
+    if (atomic_read(&ctx->external_disable_cnt)) {
+        return false;
+    }
+
+    if (npfd >= EPOLL_ENABLE_THRESHOLD) {
+        if (fdmon_epoll_try_enable(ctx)) {
+            return true;
+        } else {
+            fdmon_epoll_disable(ctx);
+        }
+    }
+    return false;
+}
+
+void fdmon_epoll_setup(AioContext *ctx)
+{
+    ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
+    if (ctx->epollfd == -1) {
+        fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno));
+    }
+}