util/fdmon-epoll.c

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * epoll(7) file descriptor monitoring
   4  */
   5
   6 #include "qemu/osdep.h"
   7 #include <sys/epoll.h>
   8 #include "qemu/rcu_queue.h"
   9 #include "aio-posix.h"
  10
  11 /* The fd number threshold to switch to epoll */
  12 #define EPOLL_ENABLE_THRESHOLD 64
  13
  14 void fdmon_epoll_disable(AioContext *ctx)
  15 {
  16     if (ctx->epollfd >= 0) {
  17         close(ctx->epollfd);
  18         ctx->epollfd = -1;
  19     }
  20
  21     /* Switch back */
  22     ctx->fdmon_ops = &fdmon_poll_ops;
  23 }
  24
  25 static inline int epoll_events_from_pfd(int pfd_events)
  26 {
  27     return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
  28            (pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
  29            (pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
  30            (pfd_events & G_IO_ERR ? EPOLLERR : 0);
  31 }
  32
  33 static void fdmon_epoll_update(AioContext *ctx,
  34                                AioHandler *old_node,
  35                                AioHandler *new_node)
  36 {
  37     struct epoll_event event = {
  38         .data.ptr = new_node,
  39         .events = new_node ? epoll_events_from_pfd(new_node->pfd.events) : 0,
  40     };
  41     int r;
  42
  43     if (!new_node) {
  44         r = epoll_ctl(ctx->epollfd, EPOLL_CTL_DEL, old_node->pfd.fd, &event);
  45     } else if (!old_node) {
  46         r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, new_node->pfd.fd, &event);
  47     } else {
  48         r = epoll_ctl(ctx->epollfd, EPOLL_CTL_MOD, new_node->pfd.fd, &event);
  49     }
  50
  51     if (r) {
  52         fdmon_epoll_disable(ctx);
  53     }
  54 }
  55
  56 static int fdmon_epoll_wait(AioContext *ctx, AioHandlerList *ready_list,
  57                             int64_t timeout)
  58 {
  59     GPollFD pfd = {
  60         .fd = ctx->epollfd,
  61         .events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR,
  62     };
  63     AioHandler *node;
  64     int i, ret = 0;
  65     struct epoll_event events[128];
  66
  67     if (timeout > 0) {
  68         ret = qemu_poll_ns(&pfd, 1, timeout);
  69         if (ret > 0) {
  70             timeout = 0;
  71         }
  72     }
  73     if (timeout <= 0 || ret > 0) {
  74         ret = epoll_wait(ctx->epollfd, events,
  75                          ARRAY_SIZE(events),
  76                          timeout);
  77         if (ret <= 0) {
  78             goto out;
  79         }
  80         for (i = 0; i < ret; i++) {
  81             int ev = events[i].events;
  82             int revents = (ev & EPOLLIN ? G_IO_IN : 0) |
  83                           (ev & EPOLLOUT ? G_IO_OUT : 0) |
  84                           (ev & EPOLLHUP ? G_IO_HUP : 0) |
  85                           (ev & EPOLLERR ? G_IO_ERR : 0);
  86
  87             node = events[i].data.ptr;
  88             aio_add_ready_handler(ready_list, node, revents);
  89         }
  90     }
  91 out:
  92     return ret;
  93 }
  94
  95 static const FDMonOps fdmon_epoll_ops = {
  96     .update = fdmon_epoll_update,
  97     .wait = fdmon_epoll_wait,
  98     .need_wait = aio_poll_disabled,
  99 };
 100
 101 static bool fdmon_epoll_try_enable(AioContext *ctx)
 102 {
 103     AioHandler *node;
 104     struct epoll_event event;
 105
 106     QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
 107         int r;
 108         if (QLIST_IS_INSERTED(node, node_deleted) || !node->pfd.events) {
 109             continue;
 110         }
 111         event.events = epoll_events_from_pfd(node->pfd.events);
 112         event.data.ptr = node;
 113         r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
 114         if (r) {
 115             return false;
 116         }
 117     }
 118
 119     ctx->fdmon_ops = &fdmon_epoll_ops;
 120     return true;
 121 }
 122
 123 bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
 124 {
 125     bool ok;
 126
 127     if (ctx->epollfd < 0) {
 128         return false;
 129     }
 130
 131     if (npfd < EPOLL_ENABLE_THRESHOLD) {
 132         return false;
 133     }
 134
 135     /* The list must not change while we add fds to epoll */
 136     if (!qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
 137         return false;
 138     }
 139
 140     ok = fdmon_epoll_try_enable(ctx);
 141
 142     qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
 143
 144     if (!ok) {
 145         fdmon_epoll_disable(ctx);
 146     }
 147     return ok;
 148 }
 149
 150 void fdmon_epoll_setup(AioContext *ctx)
 151 {
 152     ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
 153     if (ctx->epollfd == -1) {
 154         fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno));
 155     }
 156 }