[pve-devel] [PATCH v2 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 virtiofsd 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>
Tested-by: Markus Frank <m.frank at proxmox.com>
---

Changes in v2:
* fix typo in commit message
* add Markus's T-b trailer

 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