[systemd-devel] [RFC 01/12] event: allow EPOLLET as event flag

[David Herrmann]

EPOLLET enables edge-triggered mode (see epoll(7) for more). For most
use-cases, level-triggered is just fine, but for master-TTYs we need
edge-triggered to catch EPOLLHUP. master-TTYs signal EPOLLHUP if no client
is connected, but a client may connect some time later (same happens
during vhangup(2)).

However, epoll doesn't allow masking EPOLLHUP so it's signaled constantly.
To avoid this, edge-triggered mode is needed.
---
 src/libsystemd-bus/sd-event.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libsystemd-bus/sd-event.c b/src/libsystemd-bus/sd-event.c
index 6a6581b..b5ddf71 100644
--- a/src/libsystemd-bus/sd-event.c
+++ b/src/libsystemd-bus/sd-event.c
@@ -584,7 +584,7 @@ _public_ int sd_event_add_io(
 
         assert_return(e, -EINVAL);
         assert_return(fd >= 0, -EINVAL);
-        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP)), -EINVAL);
+        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET)), -EINVAL);
         assert_return(callback, -EINVAL);
         assert_return(ret, -EINVAL);
         assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
@@ -1022,7 +1022,7 @@ _public_ int sd_event_source_set_io_events(sd_event_source *s, uint32_t events)
 
         assert_return(s, -EINVAL);
         assert_return(s->type == SOURCE_IO, -EDOM);
-        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP)), -EINVAL);
+        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET)), -EINVAL);
         assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
         assert_return(!event_pid_changed(s->event), -ECHILD);
 
-- 
1.8.4.2