From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Zdenek Kabelac <zkabelac@redhat.com>
Message-ID: <7b060cd7-a4b1-04ae-3a13-0fcd8637cad6@redhat.com>
Date: Tue, 9 Jul 2019 17:06:42 +0200
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Subject: Re: [linux-lvm] lvdisplay "open" field computing
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To: LVM general discussion and development <linux-lvm@redhat.com>, Simon ELBAZ <selbaz@linagora.com>

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