[linux-lvm] Identifying useable block devices

[Peter Rajnoha]

On 01/24/2014 04:17 PM, Zdenek Kabelac wrote:
> Dne 24.1.2014 15:50, Marius Vollmer napsal(a):
>> Peter Rajnoha <prajnoha at redhat.com> writes:
>>
>>> Thanks! Well, sorry for that, I've finally noticed the thing,
>>> that was another bug, unfortunately. Should be solved now with
>>> this git head in lvm2 upstream:
>>>    89d77326170d020ebba6ae1c717c08ac4b07996a
>>> (git.fedorahosted.org/git/lvm2.git)
>>>
>>> Thing is that the pool volume *should always* be marked
>>> as private which also means DM_UDEV_DISABLE_OTHER_RULES_FLAG
>>> is set.
>>
>> Nice, thanks!
>>
>> With this fixed, I have to ask again: Is _every_ situation where a block
>> device goes from public to private with a "change" event a bug?
>>
>> I would say "yes", simply because I can't think of a situation where
>> LVM2 doesn't know from the start whether the device is creates is gonna
>> be public or private.
>>
>> If so, we just keep UDisks2 as it is, I'd say, and I file bugs when I
>> find another public->private transition.
> 
> 
> This is probably worth to put here this comment:
> 
> When lvm2 creates a complex device - it starts to build it from pieces.
> However each individual piece is initially created as a visible plain LV.
> 
> The reason behind this is - whenever lvm2 fails to finish the command
> (or someone just press Power-Off button) - it should leave metadata in
> the state, you can recover from with normal lvm2 command.
> 
> This means - even if the lvm2 fails to build complex targets - it should
> never leave metadata filled with  'private' LVs, which user cannot
> delete with lvremove command. Of course this is currently just a
> 'target' we try to reach and you are encourage to report bugs if you
> notice ordering problems here (i.e. raids are not compatible with this
> style).
> 
> So while TEMPORARY flag fixes the 'OK-path' here - it actually may
> introduce a problem of having a device with unknown content for udev in
> the case of lvm2 command problem - but the assumption here is - the
> system has far more serious troubles in such failures than you should
> care about udev-db correctness...
> 
> And there is more scary part behind this - the current NOSCAN and
> TEMPORARY flags do work only non-clustered case.

...yes, using udev in cluster is a bit of scary thing to do, I have to
admit :)

-- 
Peter