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From: "heming.zhao@suse.com" <heming.zhao@suse.com>
To: David Teigland <teigland@redhat.com>
Cc: Zdenek Kabelac <zkabelac@redhat.com>,
	LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] issue about return value in _lvchange_activate_single
Date: Wed, 18 Nov 2020 22:45:07 +0800	[thread overview]
Message-ID: <4d590441-4bf3-cd37-52c2-9fbf34a8194c@suse.com> (raw)
In-Reply-To: <20201117154516.GA18257@redhat.com>

On 11/17/20 11:45 PM, David Teigland wrote:
> On Tue, Nov 17, 2020 at 11:52:28AM +0800, heming.zhao@suse.com wrote:
>> In lvm functions, it treats "return 0" as error case.
>>
>> if _lvchange_activate() return ECMD_FAILED, the caller _lvchange_activate_single() think as normal:
>> ```
>> if (!_lvchange_activate(cmd, lv)) <== ECMD_FAILED is 5, won't enter if case.
>>          return_ECMD_FAILED;
> 
> Thanks for finding that.  In some places 0 is the error value and in other
> places ECMD_FAILED is the error value; they frequently get mixed up.
> I believe this is the bug you are seeing:
> https://sourceware.org/git/?p=lvm2.git;a=commit;h=aba9652e584b6f6a422233dea951eb59326a3de2
> 

I recommend to use a define (e.g. E_COMM_ERR) not magic number (ZERO) to replace return value. 

>> 2. node2 change the systemid to itself
>>
>> ```
>> [tb-clustermd2 ~]# vgchange -y --config "local/extra_system_ids='tb-clustermd1'" --systemid tb-clustermd2 vg1
>>    Volume group "vg1" successfully changed
>> [tb-clustermd2 ~]# lvchange -ay vg1/lv1
>> [tb-clustermd2 ~]# dmsetup ls
>> vg1-lv1 (254:0)
> 
> This is what the LVM-activate resource agent does, except it wouldn't be
> done while the LV is active on another running host.  Just wanted to
> clarify that, I don't think it's the point of your illustration here.
> 
>> 3. this time both sides have dm device.
>> ```
>> [tb-clustermd1 ~]# dmsetup ls
>> vg1-lv1 (254:0)
>> [tb-clustermd2 ~]# dmsetup ls
>> vg1-lv1 (254:0)
>> ```
> 
> For the sake of anyone looking at this later, this shouldn't happen in a
> properly running cluster.  (If you wanted the LV active on two hosts at
> once, you'd use lvmlockd and no system ID on the VG.)
> 
>> 4. node1 executes lvchange cmds. please note the return value is 0
>> ```
>> [tb-clustermd1 ~]# lvchange -ay vg1/lv1 ; echo $?
>>    WARNING: Found LVs active in VG vg1 with foreign system ID tb-clustermd2.  Possible data corruption.
>>    Cannot activate LVs in a foreign VG.
>> 0
> 
> That's the one fixed by the commit above.
> 
> Dave
> 

      reply	other threads:[~2020-11-18 14:45 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-17  3:52 [linux-lvm] issue about return value in _lvchange_activate_single heming.zhao
2020-11-17 15:45 ` David Teigland
2020-11-18 14:45   ` heming.zhao [this message]

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