[libvirt PATCH] qemu: allow passt to self-daemonize

[Laine Stump]

I initially had the passt process being started in an identical
fashion to the slirp-helper - libvirt was daemonizing the new process
and recording its pid in a pidfile. The problem with this is that,
since it is daemonized immediately, any startup error in passt happens
after the daemonization, and thus isn't seen by libvirt - libvirt
believes that the process has started successfully and continues on
its merry way. The result was that sometimes a guest would be started,
but there would be no passt process for qemu to use for network
traffic.

Instead, we should be starting passt in the same manner we start
dnsmasq - we just exec it as normal (along with a request that passt
create the pidfile, which is just another option on the passt
commandline) and wait for the child process to exit; passt then has a
chance to parse its commandline and complete all the setup prior to
daemonizing itself; if it encounters an error and exits with a non-0
code, libvirt will see the code and know about the failure. We can
then grab the output from stderr, log that so the "user" has some idea
of what went wrong, and then fail the guest startup.

Signed-off-by: Laine Stump <laine at redhat.com>
---
 src/qemu/qemu_passt.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/qemu/qemu_passt.c b/src/qemu/qemu_passt.c
index 0f09bf3db8..f640a69c00 100644
--- a/src/qemu/qemu_passt.c
+++ b/src/qemu/qemu_passt.c
@@ -141,24 +141,23 @@ qemuPasstStart(virDomainObj *vm,
     g_autofree char *passtSocketName = qemuPasstCreateSocketPath(vm, net);
     g_autoptr(virCommand) cmd = NULL;
     g_autofree char *pidfile = qemuPasstCreatePidFilename(vm, net);
+    g_autofree char *errbuf = NULL;
     char macaddr[VIR_MAC_STRING_BUFLEN];
     size_t i;
     pid_t pid = (pid_t) -1;
     int exitstatus = 0;
     int cmdret = 0;
-    VIR_AUTOCLOSE errfd = -1;
 
     cmd = virCommandNew(PASST);
 
     virCommandClearCaps(cmd);
-    virCommandSetPidFile(cmd, pidfile);
-    virCommandSetErrorFD(cmd, &errfd);
-    virCommandDaemonize(cmd);
+    virCommandSetErrorBuffer(cmd, &errbuf);
 
     virCommandAddArgList(cmd,
                          "--one-off",
                          "--socket", passtSocketName,
                          "--mac-addr", virMacAddrFormat(&net->mac, macaddr),
+                         "--pid", pidfile,
                          NULL);
 
     if (net->mtu) {
@@ -264,7 +263,7 @@ qemuPasstStart(virDomainObj *vm,
 
     if (cmdret < 0 || exitstatus != 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("Could not start 'passt'. exitstatus: %d"), exitstatus);
+                       _("Could not start 'passt': %s"), errbuf);
         goto error;
     }
 
-- 
2.39.1