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Re-write LXC controller end-of-file I/O handling yet again

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Currently the LXC controller attempts to deal with EOF on a
tty by spawning a thread to do an 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

* src/lxc/lxc_controller.c: Avoid stalled I/O upon
  connected to an LXC console
This commit is contained in:
Daniel P. Berrange 2012-01-12 17:03:03 +00:00
parent 69f0b446a8
commit 9130396214
1 changed files with 154 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

214
src/lxc/lxc_controller.c
View File

@ -736,9 +736,17 @@ struct lxcConsole {
int hostWatch;
int hostFd; /* PTY FD in the host OS */
bool hostClosed;
int hostEpoll;
bool hostBlocking;
int contWatch;
int contFd; /* PTY FD in the container */
bool contClosed;
int contEpoll;
bool contBlocking;
int epollWatch;
int epollFd; /* epoll FD for dealing with EOF */
size_t fromHostLen;
char fromHostBuf[1024];
@ -834,102 +842,148 @@ static void lxcConsoleUpdateWatch(struct lxcConsole *console)
int hostEvents = 0;
int contEvents = 0;
if (!console->hostClosed) {
if (!console->hostClosed || (!console->hostBlocking && console->fromContLen)) {
if (console->fromHostLen < sizeof(console->fromHostBuf))
hostEvents |= VIR_EVENT_HANDLE_READABLE;
if (console->fromContLen)
hostEvents |= VIR_EVENT_HANDLE_WRITABLE;
}
if (!console->contClosed) {
if (!console->contClosed || (!console->contBlocking && console->fromHostLen)) {
if (console->fromContLen < sizeof(console->fromContBuf))
contEvents |= VIR_EVENT_HANDLE_READABLE;
if (console->fromHostLen)
contEvents |= VIR_EVENT_HANDLE_WRITABLE;
}
VIR_DEBUG("Container watch %d=%d host watch %d=%d",
console->contWatch, contEvents,
console->hostWatch, hostEvents);
virEventUpdateHandle(console->contWatch, contEvents);
virEventUpdateHandle(console->hostWatch, hostEvents);
if (console->hostClosed) {
int events = EPOLLIN | EPOLLET;
if (console->hostBlocking)
events |= EPOLLOUT;
if (events != console->hostEpoll) {
struct epoll_event event;
int action = EPOLL_CTL_ADD;
if (console->hostEpoll)
action = EPOLL_CTL_MOD;
VIR_DEBUG("newHostEvents=%x oldHostEvents=%x", events, console->hostEpoll);
event.events = events;
event.data.fd = console->hostFd;
if (epoll_ctl(console->epollFd, action, console->hostFd, &event) < 0) {
VIR_DEBUG(":fail");
virReportSystemError(errno, "%s",
_("Unable to add epoll fd"));
quit = true;
goto cleanup;
}
console->hostEpoll = events;
VIR_DEBUG("newHostEvents=%x oldHostEvents=%x", events, console->hostEpoll);
}
} 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 remove epoll fd"));
VIR_DEBUG(":fail");
quit = true;
goto cleanup;
}
console->hostEpoll = 0;
}
if (console->contClosed) {
int events = EPOLLIN | EPOLLET;
if (console->contBlocking)
events |= EPOLLOUT;
if (events != console->contEpoll) {
struct epoll_event event;
int action = EPOLL_CTL_ADD;
if (console->contEpoll)
action = EPOLL_CTL_MOD;
VIR_DEBUG("newContEvents=%x oldContEvents=%x", events, console->contEpoll);
event.events = events;
event.data.fd = console->contFd;
if (epoll_ctl(console->epollFd, action, console->contFd, &event) < 0) {
virReportSystemError(errno, "%s",
_("Unable to add epoll fd"));
VIR_DEBUG(":fail");
quit = true;
goto cleanup;
}
console->contEpoll = events;
VIR_DEBUG("newHostEvents=%x oldHostEvents=%x", events, console->contEpoll);
}
} 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 remove epoll fd"));
VIR_DEBUG(":fail");
quit = true;
goto cleanup;
}
console->contEpoll = 0;
}
cleanup:
return;
}
struct lxcConsoleEOFData {
struct lxcConsole *console;
int fd;
};
static void lxcConsoleEOFThread(void *opaque)
static void lxcEpollIO(int watch, int fd, int events, void *opaque)
{
struct lxcConsoleEOFData *data = opaque;
int ret;
int epollfd = -1;
struct epoll_event event;
struct lxcConsole *console = opaque;
if ((epollfd = epoll_create(2)) < 0) {
virReportSystemError(errno, "%s",
_("Unable to create epoll fd"));
goto cleanup;
}
virMutexLock(&lock);
VIR_DEBUG("IO event watch=%d fd=%d events=%d fromHost=%zu fromcont=%zu",
watch, fd, events,
console->fromHostLen,
console->fromContLen);
event.events = EPOLLIN | EPOLLET;
event.data.fd = data->fd;
if (epoll_ctl(epollfd, EPOLL_CTL_ADD, data->fd, &event) < 0) {
virReportSystemError(errno, "%s",
_("Unable to add epoll fd"));
goto cleanup;
}
for (;;) {
ret = epoll_wait(epollfd, &event, 1, -1);
while (1) {
struct epoll_event event;
int ret;
ret = epoll_wait(console->epollFd, &event, 1, 0);
if (ret < 0) {
if (ret == EINTR)
continue;
virReportSystemError(errno, "%s",
_("Unable to wait on epoll"));
virMutexLock(&lock);
quit = true;
virMutexUnlock(&lock);
goto cleanup;
}
if (ret == 0)
break;
VIR_DEBUG("fd=%d hostFd=%d contFd=%d hostEpoll=%x contEpoll=%x",
event.data.fd, console->hostFd, console->contFd,
console->hostEpoll, console->contEpoll);
/* If we get HUP+dead PID, we just re-enable the main loop
* which will see the PID has died and exit */
if ((event.events & EPOLLIN)) {
virMutexLock(&lock);
if (event.data.fd == data->console->hostFd) {
data->console->hostClosed = false;
if (event.data.fd == console->hostFd) {
console->hostClosed = false;
} else {
data->console->contClosed = false;
console->contClosed = false;
}
lxcConsoleUpdateWatch(data->console);
virMutexUnlock(&lock);
lxcConsoleUpdateWatch(console);
break;
}
}
cleanup:
VIR_FORCE_CLOSE(epollfd);
VIR_FREE(data);
}
static int lxcCheckEOF(struct lxcConsole *console, int fd)
{
struct lxcConsoleEOFData *data;
virThread thread;
if (VIR_ALLOC(data) < 0) {
virReportOOMError();
return -1;
}
data->console = console;
data->fd = fd;
if (virThreadCreate(&thread, false, lxcConsoleEOFThread, data) < 0) {
VIR_FREE(data);
return -1;
}
return 0;
virMutexUnlock(&lock);
}
static void lxcConsoleIO(int watch, int fd, int events, void *opaque)
@ -937,6 +991,10 @@ static void lxcConsoleIO(int watch, int fd, int events, void *opaque)
struct lxcConsole *console = opaque;
virMutexLock(&lock);
VIR_DEBUG("IO event watch=%d fd=%d events=%d fromHost=%zu fromcont=%zu",
watch, fd, events,
console->fromHostLen,
console->fromContLen);
if (events & VIR_EVENT_HANDLE_READABLE) {
char *buf;
size_t *len;
@ -993,6 +1051,10 @@ static void lxcConsoleIO(int watch, int fd, int events, void *opaque)
*len -= done;
} else {
VIR_DEBUG("Write fd %d done %d errno %d", fd, (int)done, errno);
if (watch == console->hostWatch)
console->hostBlocking = true;
else
console->contBlocking = true;
}
}
@ -1003,8 +1065,6 @@ static void lxcConsoleIO(int watch, int fd, int events, void *opaque)
console->contClosed = true;
}
VIR_DEBUG("Got EOF on %d %d", watch, fd);
if (lxcCheckEOF(console, fd) < 0)
goto error;
}
lxcConsoleUpdateWatch(console);
@ -1102,10 +1162,33 @@ static int lxcControllerMain(int serverFd,
goto cleanup;
}
for (i = 0 ; i < nFds ; i++) {
consoles[i].epollFd = -1;
consoles[i].epollWatch = -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_create1(EPOLL_CLOEXEC)) < 0) {
virReportSystemError(errno, "%s",
_("Unable to create epoll fd"));
goto cleanup;
}
if ((consoles[i].epollWatch = virEventAddHandle(consoles[i].epollFd,
VIR_EVENT_HANDLE_READABLE,
lxcEpollIO,
&consoles[i],
NULL)) < 0) {
lxcError(VIR_ERR_INTERNAL_ERROR, "%s",
_("Unable to watch epoll FD"));
goto cleanup;
}
if ((consoles[i].hostWatch = virEventAddHandle(consoles[i].hostFd,
VIR_EVENT_HANDLE_READABLE,
lxcConsoleIO,
@ -1146,6 +1229,17 @@ cleanup:
cleanup2:
VIR_FORCE_CLOSE(monitor.serverFd);
VIR_FORCE_CLOSE(monitor.clientFd);
for (i = 0 ; i < nFds ; i++) {
if (consoles[i].epollWatch != -1)
virEventRemoveHandle(consoles[i].epollWatch);
VIR_FORCE_CLOSE(consoles[i].epollFd);
if (consoles[i].contWatch != -1)
virEventRemoveHandle(consoles[i].contWatch);
if (consoles[i].hostWatch != -1)
virEventRemoveHandle(consoles[i].hostWatch);
}
VIR_FREE(consoles);
return rc;
}