Re: [libvirt] [PATCH] Re-write LXC controller end-of-file I/O handling yet again

From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; Currently the LXC controller attempts to deal with EOF on a tty by spawning a thread todo a edge triggered epoll_wait().

This avoids the normal event loop spinning on POLLHUP. There is a subtle mistake though - even after seeing POLLHUP on a master PTY, it is still perfectly possible & valid to write data to the PTY. There is a buffer that can be filled with data, even when no client is present. The second mistake is that the epoll_wait() thread was not looking for the EPOLLOUT condition, so when a new client connects to the LXC console, it had to explicitly send a character before any queued output would appear. Finally, there was in fact no need to spawn a new thread to deal with epoll_wait(). The epoll file descriptor itself can be poll()'d on normally. This patch attempts to deal with all these problems. - The blocking epoll_wait() thread is replaced by a poll on the epoll file descriptor which then does a non-blocking epoll_wait() to handle events - Even if POLLHUP is seen, we continue trying to write any pending output until getting EAGAIN from write. - Once write returns EAGAIN, we modify the epoll event mask to also look for EPOLLOUT

+ } else if (console->hostEpoll) { + VIR_DEBUG("Stop epoll oldContEvents=%x", console->hostEpoll); + if (epoll_ctl(console->epollFd, EPOLL_CTL_DEL, console->hostFd, NULL) < 0) { + virReportSystemError(errno, "%s", + _("Unable to add epoll fd"));

+ } else if (console->contEpoll) { + VIR_DEBUG("Stop epoll oldContEvents=%x", console->contEpoll); + if (epoll_ctl(console->epollFd, EPOLL_CTL_DEL, console->contFd, NULL) < 0) { + virReportSystemError(errno, "%s", + _("Unable to add epoll fd"));

@@ -1103,9 +1163,32 @@ static int lxcControllerMain(int serverFd, } for (i = 0 ; i < nFds ; i++) { + consoles[i].epollFd = -1; + consoles[i].epollFd = -1;

+ consoles[i].hostWatch = -1; + consoles[i].contWatch = -1; + } + + for (i = 0 ; i < nFds ; i++) { consoles[i].hostFd = hostFds[i]; consoles[i].contFd = contFds[i]; + if ((consoles[i].epollFd = epoll_create(2)) < 0) {