[linux-lvm] lvdisplay "open" field computing

[Simon ELBAZ]

Thanks for your answer.

 From your explanation, open=2 should '"normally" not happen ?

Regards

Simon

On 09/07/2019 17:06, Zdenek Kabelac wrote:
> Dne 09. 07. 19 v 11:47 Simon ELBAZ napsal(a):
>> Hi,
>>
>> I am trying to understand how the open field is computed.
>>
>> On a CentOS6 server, lvdisplay has the following output:
>>
>> /lvdisplay /dev/mapper/vg_obm-var_spool_imap //
>> //  --- Logical volume ---//
>> //  LV Path                /dev/vg_obm/var_spool_imap//
>> //  LV Name                var_spool_imap//
>> //  VG Name                vg_obm//
>> //  LV UUID 0oK7h0-tDZH-eUxE-AyBw-cK7x-U9pS-W7X4Uh//
>> //  LV Write Access        read/write//
>> //  LV Creation host, time panoramix.ch-perrens.fr, 2015-01-16 
>> 11:03:10 +0100//
>> //  LV Status              available//
>> //  # open                 2//
>> //  LV Size                1,92 TiB//
>> //  Current LE             504572//
>> //  Segments               2//
>> //  Allocation             inherit//
>> //  Read ahead sectors     auto//
>> //  - currently set to     256//
>> //  Block device           253:3//
>> /
>>
>>   And dmsetup show the following info:
>>
>> /# dmsetup info -c | grep "253" | grep " 3"//
>> //vg_obm-var_spool_imap                 253   3 L--w    2 2 0 
>> LVM-1i1v6pEjab2WslaDQRvkf8eLk6QfBW4J0oK7h0tDZHeUxEAyBwcK7xU9pSW7X4Uh/
>>
>> Could you please give me some hint to understand how "open = 2" is 
>> obtained ?
>>
>>
>
> Hi
>
> Open field is counted in DM driver.
> Whenever device is opened - +1   - closed -1.
>
> You should be able to check 'lsof' to check and see if there are any 
> userspace openners.  But you will not see 'kernel' opens this ways.
>
> So i.e. if you mount DM device - it should be 1 open.
>
> Occasionally you can hit some bug in target drivers - then counters 
> can go crazy and become confusing - then your solution is to collect 
> as much
> info as possible - and reboot....
>
> Regards
>
> Zdenek
>