[lvm-devel] [RFC] lvmetad_is_disabled: check config before connecting to socket

[Thomas Lamprecht]

On 10/13/2017 12:06 PM, Zdenek Kabelac wrote:
> Dne 13.10.2017 v 11:08 Thomas Lamprecht napsal(a):
>> Else, lvmetad always gets started due to systemds socket auto
>> activation when executing, for example:
>>   # pvscan --cache
>> as pvscan uses lvmetad_is_disabled to check if metad is disabled
>> before connecting. This is OK for systems where systemd is not used
>> but for others, the systemd 'auto activation on socket connect'
>> feature causes the start of lvm2-lvmetad.service which is not desired
>> when disabled in the config.
>>
>> ref: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826570
>> Signed-off-by: Thomas Lamprecht <t.lamprecht at proxmox.com>
>> ---
>>
>> An alternative approach would be to just guard the lvmetad_is_disabled
>> call in tools/pvscan.c : 412 with the config check - and thus address
>> the FIXME mentioned there.
>> Would be maybe the less intrusive version?
>>
> 
> 
> Hi
> 
> The reason why is checked the presence for active service when lvmetad is disable is - we have to print warning that  lvmetad is there, but command is not going to use it/update it....

Why not just do the initial fix over a lvmetad.pid file?
Simpler and avoids auto activation.

> 
> This may considerably harm lvmetad consistency.
> 
> If you want to avoid starting lvmetad systemd service - just mask this service - that's the correct way.
> 

I must then mask also the socket as it has a require on the server.
As lvm2-monitor.service requires both, lvm2-lvmetad.service lvm2-lvmetad.socket

This then leads to a (after some time) periodic log spamming:

> Oct 10 08:17:23 dev5 systemd[1]: lvm2-monitor.service: Cannot add dependency job, ignoring: Unit lvm2-lvmetad.socket is masked.
> Oct 10 08:17:23 dev5 systemd[1]: lvm2-lvmetad.socket: Cannot add dependency job, ignoring: Unit lvm2-lvmetad.socket is masked.

So not ideal for us, our and Debian's user.

cheers,
Thomas