[pve-devel] [PATCH cluster 1/2] cluster: improve error handling when reading files

[Wolfgang Bumiller]

When querying file contents via IPC we return undef if the
file does not exist, but also on any other error. This is
potentially problematic as the ipcc_send_rec() xs function
returns undef on actual errors as well, while setting $!
(errno).

It's better to die in cases other than ENOENT. Before this,
pvesr would assume an empty replication config and an empty
vm list if pmxcfs wasn't running, which could then clear out
the entire local replication state file.
---
This patch alone already fixes the core issue with replication
states mentioned in the commit message. The the 2nd patch and
the pve-guest-common part are there mostly to avoid race
conditions between the two non-failing queries (reading the
config and querying the vm list).

 data/PVE/Cluster.pm | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/data/PVE/Cluster.pm b/data/PVE/Cluster.pm
index 84e3cbf..05f144f 100644
--- a/data/PVE/Cluster.pm
+++ b/data/PVE/Cluster.pm
@@ -2,7 +2,7 @@ package PVE::Cluster;
 
 use strict;
 use warnings;
-use POSIX qw(EEXIST);
+use POSIX qw(EEXIST ENOENT);
 use File::stat qw();
 use Socket;
 use Storable qw(dclone);
@@ -402,7 +402,8 @@ my $ipcc_get_config = sub {
     my $bindata = pack "Z*", $path;
     my $res = PVE::IPCC::ipcc_send_rec(6, $bindata);
     if (!defined($res)) {
-	return undef if ($! != 0);
+	return undef if $! == ENOENT;
+	die "$!\n" if $!;
 	return '';
     }
 
-- 
2.11.0