[pve-devel] [PATCH qemu-server 15/22] vm start/commandline: activate volumes before config_to_command()

[Fiona Ebner]

Am 16.06.25 um 13:31 schrieb DERUMIER, Alexandre via pve-devel:
>>> With '-blockdev', it is necessary to activate the volumes to generate
>>> the command line, because it can be necessary to check whether the
>>> volume is a block device or a regular file.
> 
> I was thinking about that, but do we have storage with activate_volume
> need to be done for a regular file ?
> 
> for lvm plugin for example, we could return always driver=>host_device.
> 
> activate_volume is always done in specific plugin, so the plugin should
> be able to tell if it's a block or file storage
> 
> only custom path passthrough in vm configuration need to be checked if
> it's a file or device, but we don't have activate_volume anyway

Good point! It is needed for the default implementation of
qemu_blockdev_options() in Plugin.pm. We could go ahead and have all
plugins use their own implementation of qemu_blockdev_options(), that
would avoid doing any actual IO there. That sounds good to me.

The downside is that it would break third-party plugins that would
otherwise work fine with the default implementation. But actually, it's
only those that need to do something in activate_volume() to make the
volume accessible. Maybe requiring those to provide their own
qemu_blockdev_options() implementation is an acceptable level of
breakage, not entirely sure. We could even try and just guess in the
default implementation if we cannot access the volume, maybe based on
the presence of 'path'.

@Fabian does that sound acceptable to you?