[dm-devel] 答复: why command of multipath send reinstate message to all dm's paths

[Jiaojianbing]

> > Dear Christophe,
> > when dm-105 is in one state of below, paths of dm-105 will change to
> > active if we run command of multipath.
> 
> Could you be more specific please? What multipath command did you run?
> Which version of multipath-tools are you running?

command is "multipath", which can run in shell as below:
#multipath

And the version:  multipath-tools v0.4.9 (05/33, 2016)

> >  I check code of multipath, it sends messge "reinstate_path pathname"
> > to kernel in routine reinstate_paths when status of pathgroup =
> > "PGSTATE_ENABLED/PGSTATE_UNDEF" and path's state = "PSTATE_FAILED".
> > why command of multipath do above action to all dm devices? actually,
> > parts of these paths are already offline or failed which can't be
> > recovered. Maybe we can check these devices's status by sending io to
> > these sd device at first. according to return of io, multipath send
> > reinstate to running devices and do nothing to failed devices?
> 
> I see this code in reinstate_paths():
> 
> 		vector_foreach_slot (pgp->paths, pp, j) {
> 			if (pp->state != PATH_UP &&
> 			    (pgp->status == PGSTATE_DISABLED ||
> 			     pgp->status == PGSTATE_ACTIVE))
> 				continue;
> 
> 			if (pp->dmstate == PSTATE_FAILED) {
> 				if (dm_reinstate_path(mpp->alias, pp->dev_t))
> 					condlog(0, "%s: error reinstating",
> 						pp->dev);
> 			}
> 		}
> 
> The reinstate command is only sent for paths which are either in PATH_UP
> state, or belong to an PGSTATE_ENABLED path group. I admit I'm unsure why
> all we try to reinstate paths that we know are down. This is 13-year-old code.
> 
> Interstingly, the state of your paths changes from "faulty offline" to "ready
> running". So it appears that these paths are actually _not_ down  Just the
> reinstate seems has failed on them.
> 
> multipathd -v3 logs and possibly kernel logs would be helpful to understand
> what was going on in that situation.

    Sorry, maybe my two multipath status sample confused you. They are just sample. Actually, I run command "rescan-scsi-bus" to
clear all mapped scsi devices by iscsid in host when all of LUNS in remote IPSAN are removed. 
In process of running rescan-scsi-bus, if command "multipath" is running, the status of dm's path will change from 
failed to active in some moment as below. If IO is sent to dm-105, the process who sends io will be in D state.
# multipath -ll
36d0d04b100b8cba665a187f0000000f9 dm-105 HUAWEI  ,XSG1
size=1.0G features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='service-time 0' prio=1 status=active
  `- 18:0:0:101 sdku 67:288  active faulty running

  I want to know whether command "multipath" is reasonable in reinstate_paths(). And maybe we should not call "multipath" in process of running rescan-scsi-bus ?

> Regards
> Martin
> 
> --
> Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107 SUSE Linux
> GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG
> Nürnberg)