Re: [Libvir] PATCH: Process QEMU monitor at startup
On Fri, Mar 02, 2007 at 03:06:56PM +0000, Mark McLoughlin wrote:
Hi Dan,
On Fri, 2007-03-02 at 14:35 +0000, Daniel P. Berrange wrote:
>
> +static int qemudOpenMonitor(struct qemud_vm *vm, const char *monitor)
> {
#define MONITOR_POLL_TIMEOUT 5
> + int monfd;
> + char buffer[1024];
> + int got = 0;
> +
> + if (!(monfd = open(monitor, O_RDWR))) {
> + return -1;
> + }
> + if (qemudSetCloseExec(monfd) < 0)
> + goto error;
> + if (qemudSetNonBlock(monfd) < 0)
> + goto error;
> +
> + /* Consume & discard the initial greeting */
> + for(;;) {
> + int ret;
> +
> + ret = read(monfd, buffer+got, sizeof(buffer)-got-1);
What happens if the buffer fills up ?
Sorry, wrong version of the patch - the for(;;) should have been
while (got < (sizeof(buffer)-1)) {
I'll repost the correct patch when I've done of the other fixes.
> + if (ret == 0)
> + goto error;
> + if (ret < 0) {
> + struct pollfd fd = { .fd = monfd, .events = POLLIN };
> + if (errno != EAGAIN &&
> + errno != EINTR)
> + goto error;
> +
> + ret = poll(&fd, 1, 5);
ret = poll(&fd, 1, MONITOR_POLL_TIMEOUT);
Giving up after 5 milliseconds? Are we that afraid of commitment?
Again, wrong patch - it should have been 5 seconds.
> +static int qemudWaitForMonitor(struct qemud_vm *vm) {
We don't set an error in here, so how about returning the appropriate
errno from the function?
I'll add in some error reporting.
> + if (sscanf(tmp, "char device redirected to
%19s", monitor) == 1) {
Path length of 100, maximum field with of 19? That's all rather
voodooish ... hope about strstr() to find it, buffer length of PATH_MAX
and then just strncpy()? Also, it'd be nice to split that out into e.g.
qemudMonitorPathFromStr(buffer, monitorPath, PATH_MAX)
I'll have a go at splitting it out.
> + if (qemudOpenMonitor(vm, monitor) < 0)
> + return -1;
> + return 0;
> + }
> + tmp = index(tmp, '\n');
index() is a bit odd, why not strstr() ?
Well we're only looking for a single character match - index() is for
single characters, strstr() is for strings.
> +static int qemudNextFreeVNCPort(struct qemud_server *server
> ATTRIBUTE_UNUSED) {
I don't really know the context, but it'd be much nicer if we could
just QEMU find a free port itself and then we query the port - e.g. the
obvious race condition.
Currently QEMU can't auto-allocate itself a patch - I'm planning to port
the Xen auto-allocation patch to mainline QEMU. Until then, this code is
better than the the current situation, even though there is an obvious
race.
> + if (connect(fd, (struct sockaddr*)&addr,
sizeof(addr)) == 0)
Um, why not bind() (with SO_REUSEADDR)?
No particular reason - either will work just fine.
Regards,
Dan.
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