Edge triggered epoll with pts devices acts as level triggered
From: Adam Langley (alangley_at_gmail.com)
Date: 08/12/05
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Date: Fri, 12 Aug 2005 12:19:39 +0100 To: linux-kernel@vger.kernel.org
(please cc me on replies)
Waiting for edge triggered events (with EPOLLET) on pseudo terminal
devices appears to act as if it were level triggered; when data is
ready the fd is always returned by epoll_wait.
You can test this with the code below. Compile, run and press return.
If edge triggering is working correctly a single event will be
generated, otherwise a never ending stream will start.
This works *correctly* at a real terminal, but fails for pseudo
terminals (specifically an xterm). As far as I can test with other
terminals and ssh this is a general problem with pseudo terminals.
% uname -a
Linux ice 2.6.12 #4 SMP Sun Jul 31 11:42:15 BST 2005 i686 Pentium II
(Deschutes) GenuineIntel GNU/Linux
(vanilla kernel sources)
% cat et2.c
#include <sys/epoll.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char **argv) {
const int epoll_fd = epoll_create(4);
struct epoll_event ev;
struct epoll_event events[4];
memset(&ev, 0, sizeof(ev));
ev.events = EPOLLIN | EPOLLET;
epoll_ctl(epoll_fd, EPOLL_CTL_ADD, 0, &ev);
for (;;) {
epoll_wait(epoll_fd, events, 4, -1);
write(1, ".", 1);
}
}
Thanks
AGL
-- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org (+44) (0)7906 332512 PGP: 9113 256A CC0F 71A6 4C84 5087 CDA5 52DF 2CB6 3D60 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
- Previous message: Martin Wilck: "APIC version and 8-bit APIC IDs"
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