[dm-devel] 'multipath add path' returns ok but the path is missing in the topology

[Gioh Kim]

Hi Martin,

On Wed, Apr 22, 2020 at 5:40 PM Martin Wilck <mwilck at suse.com> wrote:
>
> On Wed, 2020-04-22 at 16:00 +0200, Gioh Kim wrote:
> >
> > One question.
> > Is it possible for multipathd to generate an event for removing a
> > map?
> > I am looking into the source code, ev_add_path and some functions
> > related to add a path,
> > but it looks like it does not generate any event.
>
> I guess you mean an uevent. These events are created by the kernel when
> multipath creates or reloads maps. multipathd normally doesn't trigger
> the events directly.  But there are some cases where multipathd
> basically runs the equivalent of "udevadm trigger -c change" on either
> maps or paths. Search the code for "trigger" for details.
>
> There are also device mapper events which are created by the kernel for
> certain state changes of dm devices. Again, multipathd only receives
> such events.
>
> Regards
> Martin
>
>
>

I am making an environment to capture log for uevent as you said.

Meanwhile I found something weird: "orphan path, waiting for create to
complete" what is this message?
I guess the second added path was not registered when I executed
"multipathd add path" at this moment.

I guess there would be some time delay for the second path to be
included in the topology.
Am I right?
If I am right, could I make "multipathd add path" return only after
everything is completely finished?

Below is a log message from my test.
* multipathd add path sdc
* multipathd add path sdm
* multipathd show topology  --> There is no sdm! My test failed. I
would like to check sdm here.
* multipathd show topology  --> Now sdm is included after some mili-second.

Apr 23 11:38:25 ib1 multipathd[2132]: sdc: add path (operator)
Apr 23 11:38:25 ib1 multipathd[2132]: sdc: open node: /dev/sdc
Apr 23 11:38:25 ib1 multipathd[2132]: sdc: mpp is null
Apr 23 11:38:25 ib1 multipathd[2132]: sdc: creating new map
Apr 23 11:38:25 ib1 multipathd[2132]: sdc: open node: /dev/sdc
Apr 23 11:38:25 ib1 multipathd[2132]: sdc: domap with mpp->action=6
Apr 23 11:38:25 ib1 multipathd[2132]:
360000000000000000000000000000000: load table [0 204800 multipath 1
retain_attached_hw_handler 0 1 1 service-time 0 1 1 8:32 1]
Apr 23 11:38:25 ib1 multipathd[2132]:
360000000000000000000000000000000: event checker started
Apr 23 11:38:25 ib1 multipathd[2132]: sdc [8:32]: path added to devmap
360000000000000000000000000000000
Apr 23 11:38:25 ib1 multipathd[2132]: sdm: add path (operator)
Apr 23 11:38:25 ib1 multipathd[2132]: sdm: orphan path, waiting for
create to complete
Apr 23 11:38:25 ib1 multipathd[2132]: cli[1]: Reply [238 bytes]
Apr 23 11:38:25 ib1 multipathd[2132]: reply: [create:
360000000000000000000000000000000 dm-6 SCST_BIO,ltp-pserver3500
Apr 23 11:38:25 ib1 multipathd[2132]: size=100M features='1
retain_attached_hw_handler' hwhandler='0' wp=rw
Apr 23 11:38:25 ib1 multipathd[2132]: `-+- policy='service-time 0'
prio=1 status=enabled
Apr 23 11:38:25 ib1 multipathd[2132]:   `- 4:0:0:0 sdc 8:32  active
ready running
Apr 23 11:38:25 ib1 multipathd[2132]: ]
Apr 23 11:38:25 ib1 multipathd[2132]:
360000000000000000000000000000000: load table [0 204800 multipath 1
retain_attached_hw_handler 0 1 1 service-time 0 2 1 8:32 1 8:192 1]
Apr 23 11:38:25 ib1 multipathd[2132]: cli[1]: Reply [274 bytes]
Apr 23 11:38:25 ib1 multipathd[2132]: reply:
[360000000000000000000000000000000 dm-6 SCST_BIO,ltp-pserver3500
Apr 23 11:38:25 ib1 multipathd[2132]: size=100M features='1
retain_attached_hw_handler' hwhandler='0' wp=rw
Apr 23 11:38:25 ib1 multipathd[2132]: `-+- policy='service-time 0'
prio=1 status=enabled
Apr 23 11:38:25 ib1 multipathd[2132]:   |- 4:0:0:0 sdc 8:32  active
ready running
Apr 23 11:38:25 ib1 multipathd[2132]:   `- 5:0:0:0 sdm 8:192 active
ready running
Apr 23 11:38:25 ib1 multipathd[2132]: ]



-- 
Gioh Kim

Cloud server kernel maintainer
Quality Management (IONOS Cloud)

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