[pve-devel] [PATCH v5 container 2/4] clone_vm: improve config locking

[Oguz Bektas]

cleaned up the locking situation with config files as Fabian G.
suggested in the review.

use the 'create_and_lock_config' helper in the beginning to ensure that
the target CTID is available, and that the target config is locked from
the beginning. in case any error happens during the initial checks, we
unlink this config in error handling.

firewall config is also now cloned inside the worker instead of before
the worker, in case the clone fails.

also lock the config file when renaming the conf (for moving to a target
node when the option is passed).

Signed-off-by: Oguz Bektas <o.bektas at proxmox.com>
---
v4->v5:
* move create_and_lock_config outside the eval
* also lock moving config to target node



 src/PVE/API2/LXC.pm | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/src/PVE/API2/LXC.pm b/src/PVE/API2/LXC.pm
index 936debb..ade109b 100644
--- a/src/PVE/API2/LXC.pm
+++ b/src/PVE/API2/LXC.pm
@@ -1394,6 +1394,9 @@ __PACKAGE__->register_method({
 	my $vollist = [];
 	my $running;
 
+	PVE::LXC::Config->create_and_lock_config($newid, 0);
+	$conffile = PVE::LXC::Config->config_file($newid);
+
 	PVE::LXC::Config->lock_config($vmid, sub {
 	    my $src_conf = PVE::LXC::Config->set_lock($vmid, 'disk');
 
@@ -1411,10 +1414,6 @@ __PACKAGE__->register_method({
 
 		my $src_conf = $snapname ? $src_conf->{snapshots}->{$snapname} : $src_conf;
 
-		$conffile = PVE::LXC::Config->config_file($newid);
-		die "unable to create CT $newid: config file already exists\n"
-		    if -f $conffile;
-
 		my $sharedvm = 1;
 		for my $opt (sort keys %$src_conf) {
 		    next if $opt =~ m/^unused\d+$/;
@@ -1482,11 +1481,23 @@ __PACKAGE__->register_method({
 		    $newconf->{description} = $param->{description};
 		}
 
-		# create empty/temp config - this fails if CT already exists on other node
-		PVE::LXC::Config->write_config($newid, $newconf);
+		PVE::LXC::Config->lock_config($newid, sub {
+		    # read empty config, lock needs to be still here
+		    my $conf = PVE::LXC::Config->load_config($newid);
+		    die "Lost 'create' config lock, aborting.\n"
+			if !PVE::LXC::Config->has_lock($conf, 'create');
+		    # write the actual new config now to disk
+		    PVE::LXC::Config->write_config($newid, $newconf);
+		});
 	    };
 	    if (my $err = $@) {
 		eval { PVE::LXC::Config->remove_lock($vmid, 'disk') };
+		PVE::LXC::Config->lock_config($newid, sub {
+		    my $conf = PVE::LXC::Config->load_config($newid);
+		    die "Lost 'create' config lock, aborting.\n"
+			if !PVE::LXC::Config->has_lock($conf, 'create');
+		    unlink($conffile);
+		});
 		warn $@ if $@;
 		die $err;
 	    }
@@ -1545,18 +1556,19 @@ __PACKAGE__->register_method({
 		PVE::AccessControl::add_vm_to_pool($newid, $pool) if $pool;
 		PVE::LXC::Config->remove_lock($newid, 'create');
 
-		if ($target) {
-		    # always deactivate volumes - avoid lvm LVs to be active on several nodes
-		    PVE::Storage::deactivate_volumes($storecfg, $vollist, $snapname) if !$running;
-		    PVE::Storage::deactivate_volumes($storecfg, $newvollist);
+		PVE::LXC::Config->lock_config($newid, sub {
+		    if ($target) {
+			# always deactivate volumes - avoid lvm LVs to be active on several nodes
+			PVE::Storage::deactivate_volumes($storecfg, $vollist, $snapname) if !$running;
+			PVE::Storage::deactivate_volumes($storecfg, $newvollist);
 
-		    my $newconffile = PVE::LXC::Config->config_file($newid, $target);
-		    die "Failed to move config to node '$target' - rename failed: $!\n"
-			if !rename($conffile, $newconffile);
-		}
+			my $newconffile = PVE::LXC::Config->config_file($newid, $target);
+			die "Failed to move config to node '$target' - rename failed: $!\n"
+			    if !rename($conffile, $newconffile);
+		    }
+		});
 	    };
 	    my $err = $@;
-
 	    # Unlock the source config in any case:
 	    eval { PVE::LXC::Config->remove_lock($vmid, 'disk') };
 	    warn $@ if $@;
@@ -1574,10 +1586,10 @@ __PACKAGE__->register_method({
 		die "clone failed: $err";
 	    }
 
+	    PVE::Firewall::clone_vmfw_conf($vmid, $newid);
 	    return;
 	};
 
-	PVE::Firewall::clone_vmfw_conf($vmid, $newid);
 	return $rpcenv->fork_worker('vzclone', $vmid, $authuser, $realcmd);
     }});
 
-- 
2.20.1