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authorRusty Russell <rusty@rustcorp.com.au>2008-07-29 09:58:38 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-07-29 09:58:39 +1000
commit8c79873da0d2bedf4ad6b868c54e426bb0a2fe38 (patch)
tree270efee346b70ae6615dd4796363479c94eca6d9
parent0f0c4fab8284f3b886b2e1e0e317e3bb8de176b3 (diff)
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lguest: turn Waker into a thread, not a process
lguest uses a Waker process to break it out of the kernel (ie. actually running the guest) when file descriptor needs attention. Changing this from a process to a thread somewhat simplifies things: it can directly access the fd_set of things to watch. More importantly, it means that the Waker can see Guest memory correctly, so /dev/vring file descriptors will work as anticipated (the alternative is to actually mmap MAP_SHARED, but you can't do that with /dev/zero). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r--Documentation/lguest/lguest.c120
1 files changed, 57 insertions, 63 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index f9bba2d8fee1..b88b0ea54e90 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -76,8 +76,12 @@ static bool verbose;
do { if (verbose) printf(args); } while(0)
/*:*/
-/* The pipe to send commands to the waker process */
-static int waker_fd;
+/* File descriptors for the Waker. */
+struct {
+ int pipe[2];
+ int lguest_fd;
+} waker_fds;
+
/* The pointer to the start of guest memory. */
static void *guest_base;
/* The maximum guest physical address allowed, and maximum possible. */
@@ -579,69 +583,64 @@ static void add_device_fd(int fd)
* watch, but handing a file descriptor mask through to the kernel is fairly
* icky.
*
- * Instead, we fork off a process which watches the file descriptors and writes
+ * Instead, we clone off a thread which watches the file descriptors and writes
* the LHREQ_BREAK command to the /dev/lguest file descriptor to tell the Host
* stop running the Guest. This causes the Launcher to return from the
* /dev/lguest read with -EAGAIN, where it will write to /dev/lguest to reset
* the LHREQ_BREAK and wake us up again.
*
* This, of course, is merely a different *kind* of icky.
+ *
+ * Given my well-known antipathy to threads, I'd prefer to use processes. But
+ * it's easier to share Guest memory with threads, and trivial to share the
+ * devices.infds as the Launcher changes it.
*/
-static void wake_parent(int pipefd, int lguest_fd)
+static int waker(void *unused)
{
- /* Add the pipe from the Launcher to the fdset in the device_list, so
- * we watch it, too. */
- add_device_fd(pipefd);
+ /* Close the write end of the pipe: only the Launcher has it open. */
+ close(waker_fds.pipe[1]);
for (;;) {
fd_set rfds = devices.infds;
unsigned long args[] = { LHREQ_BREAK, 1 };
+ unsigned int maxfd = devices.max_infd;
+
+ /* We also listen to the pipe from the Launcher. */
+ FD_SET(waker_fds.pipe[0], &rfds);
+ if (waker_fds.pipe[0] > maxfd)
+ maxfd = waker_fds.pipe[0];
/* Wait until input is ready from one of the devices. */
- select(devices.max_infd+1, &rfds, NULL, NULL, NULL);
- /* Is it a message from the Launcher? */
- if (FD_ISSET(pipefd, &rfds)) {
- int fd;
- /* If read() returns 0, it means the Launcher has
- * exited. We silently follow. */
- if (read(pipefd, &fd, sizeof(fd)) == 0)
- exit(0);
- /* Otherwise it's telling us to change what file
- * descriptors we're to listen to. Positive means
- * listen to a new one, negative means stop
- * listening. */
- if (fd >= 0)
- FD_SET(fd, &devices.infds);
- else
- FD_CLR(-fd - 1, &devices.infds);
- } else /* Send LHREQ_BREAK command. */
- pwrite(lguest_fd, args, sizeof(args), cpu_id);
+ select(maxfd+1, &rfds, NULL, NULL, NULL);
+
+ /* Message from Launcher? */
+ if (FD_ISSET(waker_fds.pipe[0], &rfds)) {
+ char c;
+ /* If this fails, then assume Launcher has exited.
+ * Don't do anything on exit: we're just a thread! */
+ if (read(waker_fds.pipe[0], &c, 1) != 1)
+ _exit(0);
+ continue;
+ }
+
+ /* Send LHREQ_BREAK command to snap the Launcher out of it. */
+ pwrite(waker_fds.lguest_fd, args, sizeof(args), cpu_id);
}
+ return 0;
}
/* This routine just sets up a pipe to the Waker process. */
-static int setup_waker(int lguest_fd)
-{
- int pipefd[2], child;
-
- /* We create a pipe to talk to the Waker, and also so it knows when the
- * Launcher dies (and closes pipe). */
- pipe(pipefd);
- child = fork();
- if (child == -1)
- err(1, "forking");
-
- if (child == 0) {
- /* We are the Waker: close the "writing" end of our copy of the
- * pipe and start waiting for input. */
- close(pipefd[1]);
- wake_parent(pipefd[0], lguest_fd);
- }
- /* Close the reading end of our copy of the pipe. */
- close(pipefd[0]);
+static void setup_waker(int lguest_fd)
+{
+ /* This pipe is closed when Launcher dies, telling Waker. */
+ if (pipe(waker_fds.pipe) != 0)
+ err(1, "Creating pipe for Waker");
- /* Here is the fd used to talk to the waker. */
- return pipefd[1];
+ /* Waker also needs to know the lguest fd */
+ waker_fds.lguest_fd = lguest_fd;
+
+ if (clone(waker, malloc(4096) + 4096, CLONE_VM | SIGCHLD, NULL) == -1)
+ err(1, "Creating Waker");
}
/*
@@ -863,8 +862,8 @@ static bool handle_console_input(int fd, struct device *dev)
unsigned long args[] = { LHREQ_BREAK, 0 };
/* Close the fd so Waker will know it has to
* exit. */
- close(waker_fd);
- /* Just in case waker is blocked in BREAK, send
+ close(waker_fds.pipe[1]);
+ /* Just in case Waker is blocked in BREAK, send
* unbreak now. */
write(fd, args, sizeof(args));
exit(2);
@@ -996,8 +995,8 @@ static bool handle_tun_input(int fd, struct device *dev)
static void enable_fd(int fd, struct virtqueue *vq, bool timeout)
{
add_device_fd(vq->dev->fd);
- /* Tell waker to listen to it again */
- write(waker_fd, &vq->dev->fd, sizeof(vq->dev->fd));
+ /* Snap the Waker out of its select loop. */
+ write(waker_fds.pipe[1], "", 1);
}
static void net_enable_fd(int fd, struct virtqueue *vq, bool timeout)
@@ -1134,7 +1133,6 @@ static void handle_input(int fd)
* descriptors and a method of handling them. */
for (i = devices.dev; i; i = i->next) {
if (i->handle_input && FD_ISSET(i->fd, &fds)) {
- int dev_fd;
if (i->handle_input(fd, i))
continue;
@@ -1144,11 +1142,6 @@ static void handle_input(int fd)
* buffers to deliver into. Console also uses
* it when it discovers that stdin is closed. */
FD_CLR(i->fd, &devices.infds);
- /* Tell waker to ignore it too, by sending a
- * negative fd number (-1, since 0 is a valid
- * FD number). */
- dev_fd = -i->fd - 1;
- write(waker_fd, &dev_fd, sizeof(dev_fd));
}
}
@@ -1880,11 +1873,12 @@ static void __attribute__((noreturn)) restart_guest(void)
{
unsigned int i;
- /* Closing pipes causes the Waker thread and io_threads to die, and
- * closing /dev/lguest cleans up the Guest. Since we don't track all
- * open fds, we simply close everything beyond stderr. */
+ /* Since we don't track all open fds, we simply close everything beyond
+ * stderr. */
for (i = 3; i < FD_SETSIZE; i++)
close(i);
+
+ /* The exec automatically gets rid of the I/O and Waker threads. */
execv(main_args[0], main_args);
err(1, "Could not exec %s", main_args[0]);
}
@@ -2085,10 +2079,10 @@ int main(int argc, char *argv[])
* /dev/lguest file descriptor. */
lguest_fd = tell_kernel(pgdir, start);
- /* We fork off a child process, which wakes the Launcher whenever one
- * of the input file descriptors needs attention. We call this the
- * Waker, and we'll cover it in a moment. */
- waker_fd = setup_waker(lguest_fd);
+ /* We clone off a thread, which wakes the Launcher whenever one of the
+ * input file descriptors needs attention. We call this the Waker, and
+ * we'll cover it in a moment. */
+ setup_waker(lguest_fd);
/* Finally, run the Guest. This doesn't return. */
run_guest(lguest_fd);