[PATCH storage v4 2/2] nfs: use rpcinfo as a showmount fallback for nfs3

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

The check_connection call must succeed in order for the NFS storage to
be activated. In a setup in which the NFS server does not list exports
and which only supports NFSv3 this would result in the storage not being
usable (not without manually mounting the NFS share and using a
Directory storage instead). We add a fallback check with rpcinfo for
this case.

The rpcinfo check was replaced with showmount in f8b0d82f. At the time
the rationale was that rpcinfo did not have support for ipv6
connections, which does not hold anymore.

In order to not break compatibility with setups that already activate
correctly, we add a rpcinfo check as a fallback for NFSv3-only setups
only after the showmount command fails.

Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
---
 src/PVE/Storage/NFSPlugin.pm | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/PVE/Storage/NFSPlugin.pm b/src/PVE/Storage/NFSPlugin.pm
index 56dbd9ec..4fe7695a 100644
--- a/src/PVE/Storage/NFSPlugin.pm
+++ b/src/PVE/Storage/NFSPlugin.pm
@@ -198,6 +198,11 @@ sub check_connection {
         # no exports are listed
         $cmd = $nfs_get_rpcinfo_command->($server, '4');
     } else {
+        # FIXME: PVE 10: Consider switching to rpcinfo altogether.
+        # There are some potential pitfalls:
+        # - Some NFSv3 servers might only support UDP (cf. RFC 1813, Section 2.3)
+        # - The two timeouts add up to a potential worst-case scenario of 20 seconds
+        # - Some NFSv4-only servers might not have rpcbind as described at commit acff8954
         $cmd = ['/sbin/showmount', '--no-headers', '--exports', $server];
     }
 
@@ -214,6 +219,12 @@ sub check_connection {
             return 0 if $port == 0;
 
             return PVE::Network::tcp_ping($server, $port, 2);
+        } else {
+            $cmd = $nfs_get_rpcinfo_command->($server, '3');
+            eval {
+                run_command($cmd, timeout => 10, outfunc => sub { }, errfunc => sub { });
+            };
+            return 1 if !$@;
         }
         return 0;
     }
-- 
2.47.3