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qrap: Add probe retry on connection reset from passt for KubeVirt integration

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KubeVirt uses libvirt to start qrap in its current draft integration
(https://github.com/kubevirt/kubevirt/pull/7849/), and libvirtd
starts qrap three times every time a new virtual machine is created:
once on domain creation, and twice on domain start (for "probing")
and to finally start it for real.

Very often, a subsequent invocation of qrap happen before the
previously running instance of qemu terminates, which means that
passt will refuse the new connection as the old one is still active.

Introduce a single retry with a 100ms delay to work around this. This
should be checked again once native libvirt support is there, and
that point qrap will have no reason to exist anymore.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2022-06-16 15:00:06 +02:00
parent 721fa1bf5d
commit fca5e11773
1 changed files with 33 additions and 1 deletions
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34
qrap.c
View file

@ -25,6 +25,7 @@
#include <net/if_arp.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <time.h>
#include "util.h"
#include "passt.h"
@ -112,7 +113,7 @@ void usage(const char *name)
int main(int argc, char **argv)
{
struct timeval tv = { .tv_sec = 0, .tv_usec = (long)(500 * 1000) };
int i, s, qemu_argc = 0, addr_map = 0, has_dev = 0;
int i, s, qemu_argc = 0, addr_map = 0, has_dev = 0, retry_on_reset;
char *qemu_argv[ARG_MAX], dev_str[ARG_MAX];
struct sockaddr_un addr = {
.sun_family = AF_UNIX,
@ -233,6 +234,9 @@ int main(int argc, char **argv)
valid_args:
for (i = 1; i < UNIX_SOCK_MAX; i++) {
retry_on_reset = 1;
retry:
s = socket(AF_UNIX, SOCK_STREAM, 0);
if (s < 0) {
perror("socket");
@ -254,6 +258,34 @@ valid_args:
else
break;
/* FIXME: in a KubeVirt environment, libvirtd invokes qrap three
* times in a strict sequence when a virtual machine needs to
* be started, namely, when:
* - the domain XML is saved
* - the domain is started (for "probing")
* - the virtual machine is started for real
* and it often happens that the qemu process is still running
* when qrap is invoked again, so passt will refuse the new
* connection because the previous one is still active. This
* overlap seems to be anywhere between 0 and 3ms.
*
* If we get a connection reset, retry, just once, after 100ms,
* to allow for the previous qemu instance to terminate and, in
* turn, for the connection to passt to be closed.
*
* This should be fixed in libvirt instead. It probably makes
* sense to check this behaviour once native libvirt support is
* there, and this implies native qemu support too, so at that
* point qrap will have no reason to exist anymore -- that is,
* this FIXME will probably remain until the tool itself is
* obsoleted.
*/
if (retry_on_reset && errno == ECONNRESET) {
retry_on_reset = 0;
usleep(100 * 1000);
goto retry;
}
fprintf(stderr, "Probe of %s failed\n", addr.sun_path);
close(s);