[pve-devel] [PATCH qemu-server] virtiofs: prevent issue with Windows OS and too many files

[Fiona Ebner]

As reported in the community forum [0] and the virtio-win project [1],
virtiofsd will run into its open file limit when used with a Windows
guest that reads too many files. It's also reported that the issue
does not occur with Linux guests and a workaround is using
'--inode-file-handles=mandatory' on virtiofsd command line.

The option is described as follows in the vritiofsd help:

> When to use file handles to reference inodes instead of O_PATH file
> descriptors (never, prefer, mandatory)

and the default is 'never'.

Fix the above issue by using 'prefer' rather than 'mandatory', because
that should not break other edge cases:

> prefer: Attempt to generate file handles, but fall back to O_PATH
> file descriptors where the underlying filesystem does not support
> file handles. Useful when there are various different filesystems
> under the shared directory and some of them do not support file
> handles.

[0]: https://forum.proxmox.com/threads/165565/
[1]: https://github.com/virtio-win/kvm-guest-drivers-windows/issues/1136

Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

Didn't get around to measure the performance impact yet, so feel free
to check that if you test this patch. While not being broken is more
important than good performance, it would still be good to know for
completeness.

 PVE/QemuServer/Virtiofs.pm | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/PVE/QemuServer/Virtiofs.pm b/PVE/QemuServer/Virtiofs.pm
index cfde92c9..5a91b23a 100644
--- a/PVE/QemuServer/Virtiofs.pm
+++ b/PVE/QemuServer/Virtiofs.pm
@@ -130,14 +130,17 @@ sub start_all_virtiofsd {
 	next if !$conf->{$opt};
 	my $virtiofs = parse_property_string('pve-qm-virtiofs', $conf->{$opt});
 
-	my $virtiofs_socket = start_virtiofsd($vmid, $i, $virtiofs);
+	# See https://github.com/virtio-win/kvm-guest-drivers-windows/issues/1136
+	my $prefer_inode_fh = PVE::QemuServer::Helpers::windows_version($conf->{ostype}) ? 1 : 0;
+
+	my $virtiofs_socket = start_virtiofsd($vmid, $i, $virtiofs, $prefer_inode_fh);
 	push @$virtiofs_sockets, $virtiofs_socket;
     }
     return $virtiofs_sockets;
 }
 
 sub start_virtiofsd {
-    my ($vmid, $fsid, $virtiofs) = @_;
+    my ($vmid, $fsid, $virtiofs, $prefer_inode_fh) = @_;
 
     mkdir $socket_path_root;
     my $socket_path = "$socket_path_root/vm$vmid-fs$fsid";
@@ -175,6 +178,7 @@ sub start_virtiofsd {
 	    push @$cmd, '--announce-submounts';
 	    push @$cmd, '--allow-direct-io' if $virtiofs->{'direct-io'};
 	    push @$cmd, '--cache='.$virtiofs->{cache} if $virtiofs->{cache};
+	    push @$cmd, '--inode-file-handles=prefer' if $prefer_inode_fh;
 	    push @$cmd, '--syslog';
 	    exec(@$cmd);
 	} elsif (!defined($pid2)) {
-- 
2.39.5