[pve-devel] [RFC container] Improve feedback for startup

[Fabian Ebner <f.ebner@proxmox.com>]

Since it was necessary to switch to 'Type=Simple' in the systemd
service (see 545d6f0a13ac2bf3a8d3f224c19c0e0def12116d ),
'systemctl start pve-container@ID' would not wait for the 'lxc-start'
command anymore. Thus every container start was reported as a success
and the 'post-start' hook would trigger immediately after the
'systemctl start' command.

Use 'lxc-monitor' to get the necessary information and detect
startup failure and only run the 'post-start' hookscript after
the container is effectively running. If something goes wrong
with the monitor, fall back to the old behavior.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
---
 src/PVE/LXC.pm | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
index db5b8ca..35dc54c 100644
--- a/src/PVE/LXC.pm
+++ b/src/PVE/LXC.pm
@@ -2191,10 +2191,44 @@ sub vm_start {
 
     PVE::Storage::activate_volumes($storage_cfg, $vollist);
 
+    my $monitor_pid = open(my $monitor_fh, '-|', "/usr/bin/lxc-monitor -n $vmid")
+	or warn "could not open pipe to lxc-monitor\n";
+
     my $cmd = ['systemctl', 'start', "pve-container\@$vmid"];
 
     PVE::GuestHelpers::exec_hookscript($conf, $vmid, 'pre-start', 1);
-    eval { PVE::Tools::run_command($cmd); };
+    eval {
+	PVE::Tools::run_command($cmd);
+
+	my $success;
+	if ($monitor_pid) {
+	    eval {
+		local $SIG{ALRM} = sub { die "got timeout\n" };
+		alarm(10); # 'STARTING' should appear quickly
+
+		while (my $line = <$monitor_fh>) {
+		    if ($line =~ m/^'$vmid' changed state to \[([A-Z]*)\]$/) {
+			my $status = $1;
+			alarm(0);
+			$success = 1 if $status eq 'RUNNING';
+			$success = 0 if $status eq 'ABORTING'
+				     || $status eq 'STOPPING'
+				     || $status eq 'STOPPED';
+			if (defined($success)) {
+			    kill('KILL', $monitor_pid);
+			    waitpid($monitor_pid, 0);
+			}
+		    } else {
+			die "unexpected output from lxc-monitor: $line\n";
+		    }
+		}
+	    };
+	    warn "Problem with lxc-monitor: $@" if $@;
+	    alarm(0);
+	}
+	die "'lxc-start' failed for container '$vmid'\n"
+	    if defined($success) && !$success;
+    };
     if (my $err = $@) {
 	unlink $skiplock_flag_fn;
 	die $err;
-- 
2.20.1