Re: [pve-devel] [PATCH qemu-server 2/6] drive: factor out read-only helper

[Stefan Reiter <s.reiter@proxmox.com>]

On 6/7/21 12:23 PM, Fabian Grünbichler wrote:
> On June 7, 2021 11:29 am, Stefan Reiter wrote:
>> On 6/4/21 11:47 AM, Fabian Grünbichler wrote:
>>> we also need it for efidisks.
>>>
>>> Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
>>> ---
>>>    PVE/QemuServer.pm       |  8 ++------
>>>    PVE/QemuServer/Drive.pm | 10 ++++++++++
>>>    2 files changed, 12 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
>>> index 25ac052..0d49415 100644
>>> --- a/PVE/QemuServer.pm
>>> +++ b/PVE/QemuServer.pm
>>> @@ -48,7 +48,7 @@ use PVE::QemuServer::Helpers qw(min_version config_aware_timeout);
>>>    use PVE::QemuServer::Cloudinit;
>>>    use PVE::QemuServer::CGroup;
>>>    use PVE::QemuServer::CPUConfig qw(print_cpu_device get_cpu_options);
>>> -use PVE::QemuServer::Drive qw(is_valid_drivename drive_is_cloudinit drive_is_cdrom parse_drive print_drive);
>>> +use PVE::QemuServer::Drive qw(is_valid_drivename drive_is_cloudinit drive_is_cdrom drive_is_read_only parse_drive print_drive);
>>>    use PVE::QemuServer::Machine;
>>>    use PVE::QemuServer::Memory;
>>>    use PVE::QemuServer::Monitor qw(mon_cmd);
>>> @@ -3662,11 +3662,7 @@ sub config_to_command {
>>>    	my $drive_cmd = print_drive_commandline_full($storecfg, $vmid, $drive, $pbs_name);
>>>    
>>>    	# extra protection for templates, but SATA and IDE don't support it..
>>> -	my $read_only = PVE::QemuConfig->is_template($conf)
>>> -	    && $drive->{interface} ne 'sata'
>>> -	    && $drive->{interface} ne 'ide';
>>> -
>>> -	$drive_cmd .= ',readonly=on' if $read_only;
>>> +	$drive_cmd .= ',readonly=on' if drive_is_read_only($conf, $drive);
>>>    
>>>    	push @$devices, '-drive',$drive_cmd;
>>>    	push @$devices, '-device', print_drivedevice_full(
>>> diff --git a/PVE/QemuServer/Drive.pm b/PVE/QemuServer/Drive.pm
>>> index 146a4ab..0408e32 100644
>>> --- a/PVE/QemuServer/Drive.pm
>>> +++ b/PVE/QemuServer/Drive.pm
>>> @@ -12,6 +12,7 @@ our @EXPORT_OK = qw(
>>>    is_valid_drivename
>>>    drive_is_cloudinit
>>>    drive_is_cdrom
>>> +drive_is_read_only
>>>    parse_drive
>>>    print_drive
>>>    );
>>> @@ -422,6 +423,15 @@ sub drive_is_cdrom {
>>>        return $drive && $drive->{media} && ($drive->{media} eq 'cdrom');
>>>    }
>>>    
>>> +sub drive_is_read_only {
>>
>> I really don't like this name, this checks if the drive *should* be
>> read-only, and only related to template backups, not in general.
> 
> yeah, `drive_should_be_read_only` would be more apt, but also sounds
> wrong. I did have the non-template case in mind as well (e.g., adding a
> 'ro' flag to the drive in our VM config as a future addon, like we have
> for container mountpoints).
> 

Yes, I actually assumed we could already do that before I looked more 
closely when reviewing your patches :)

>>
>> Maybe 'drive_template_read_only'?
>>
>> The function does two pretty unrelated things in general IMO, so maybe
>> it would be clearer to do the is_template check at call site and make
>> this 'drive_supports_read_only', even if it causes a little bit more
>> duplication.
> 
> would work as well. or we drop all of it and no longer mark any drives
> as read-only, if we use the patch that adds '-snapshot' for
> 'start-template-for-backup'? at the risk of re-doing it if we ever add a
> 'ro' property for individual regular disks/drives..
> 

Hm, I do like the idea of marking them read-only if possible, even if we 
pass '-snapshot' - all of this is just preventative anyway, as the guest 
is stopped and should never write anything, so at this point might as 
well make it in-depth if it's cheap like here. And potentially reuseable 
for a ro flag.

>>
>>> +    my ($conf, $drive) = @_;
>>> +
>>> +    return 0 if !PVE::QemuConfig->is_template($conf);
>>> +
>>> +    # don't support being marked read-only
>>> +    return $drive->{interface} ne 'sata' && $drive->{interface} ne 'ide';
>>> +}
>>> +
>>>    # ideX = [volume=]volume-id[,media=d][,cyls=c,heads=h,secs=s[,trans=t]]
>>>    #        [,snapshot=on|off][,cache=on|off][,format=f][,backup=yes|no]
>>>    #        [,rerror=ignore|report|stop][,werror=enospc|ignore|report|stop]
>>>
>>