[pve-devel] [PATCH storage 1/2] fix #5779: rbd: allow to pass custom krbd map options

[Friedrich Weber]

When KRBD is enabled for an RBD storage, the storage plugin calls out
to `rbd map` to map an RBD image as a block device on the host.
Sometimes it might be necessary to pass custom options to `rbd map`.
For instance, in some setups with Windows VMs, KRBD logs `bad
crc/signature` and VMs performance is degraded unless the `rxbounce`
option is enabled, as reported in the forum [1].

To allow users to specify custom options for KRBD, introduce a
corresponding `krbd-map-options` property to the RBD plugin. The
property is designed to only accept a supported set of map options.
For now, this is only the `rxbounce` map option, but the supported set
can be extended in the future.

The reasoning for constraining the supported set of map options
instead of allowing to pass a free-form option string is as follows:
If `rxbounce` turns out to be a sensible default, accepting a
free-form option string now will make it hard to switch over the
default to `rxbounce` while still allowing users to disable `rxbounce`
if needed. This would require scanning the free-form string for a
`norxbounce` or similar, which is cumbersome.

If users need to set a map option that `krbd-map-options` does not
support (yet), they can alternatively set the RBD config option
`rbd_default_map_options` [2].

[1] https://forum.proxmox.com/threads/155741/
[2] https://github.com/ceph/ceph/blob/b2a4bd840/src/common/options/rbd.yaml.in#L507

Signed-off-by: Friedrich Weber <f.weber at proxmox.com>
---
 src/PVE/Storage/Plugin.pm    | 10 ++++++++++
 src/PVE/Storage/RBDPlugin.pm | 14 +++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Storage/Plugin.pm b/src/PVE/Storage/Plugin.pm
index 8cc693c..02be257 100644
--- a/src/PVE/Storage/Plugin.pm
+++ b/src/PVE/Storage/Plugin.pm
@@ -394,6 +394,16 @@ sub verify_dir_override {
     die "invalid override '$value'\n";
 }
 
+PVE::JSONSchema::register_format('pve-storage-krbd-map-option', \&verify_krbd_map_option);
+sub verify_krbd_map_option {
+    my ($option, $noerr) = @_;
+
+    return $option if $option eq 'rxbounce';
+
+    return undef if $noerr;
+    die "invalid krbd map option '$option'\n";
+}
+
 sub private {
     return $defaultData;
 }
diff --git a/src/PVE/Storage/RBDPlugin.pm b/src/PVE/Storage/RBDPlugin.pm
index f45ad3f..8110cff 100644
--- a/src/PVE/Storage/RBDPlugin.pm
+++ b/src/PVE/Storage/RBDPlugin.pm
@@ -394,6 +394,12 @@ sub properties {
 	    description => "Client keyring contents (for external clusters).",
 	    type => 'string',
 	},
+	'krbd-map-options' => {
+	    description => "Additional map options (only for krbd). Supported:"
+		." rxbounce.",
+	    type => 'string',
+	    format => 'pve-storage-krbd-map-option-list',
+	},
     };
 }
 
@@ -410,6 +416,7 @@ sub options {
 	krbd => { optional => 1 },
 	keyring => { optional => 1 },
 	bwlimit => { optional => 1 },
+	'krbd-map-options' => { optional => 1 },
     };
 }
 
@@ -726,7 +733,12 @@ sub map_volume {
     # features can only be enabled/disabled for image, not for snapshot!
     $krbd_feature_update->($scfg, $storeid, $img_name);
 
-    my $cmd = $rbd_cmd->($scfg, $storeid, 'map', $name);
+    my @additional_options = ();
+    if ($scfg->{'krbd-map-options'}) {
+	@additional_options = ('--options', $scfg->{'krbd-map-options'});
+    }
+
+    my $cmd = $rbd_cmd->($scfg, $storeid, 'map', $name, @additional_options);
     run_rbd_command($cmd, errmsg => "can't map rbd volume $name");
 
     return $kerneldev;
-- 
2.39.5