Re: mdadm --wait returns while array under construction? [patch question]

[NeilBrown <neilb@suse.de>]

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On Tue, 27 Nov 2012 10:28:33 -0800 Ross Boylan <ross@biostat.ucsf.edu> wrote:

> On Wed, 2012-11-21 at 08:43 +1100, NeilBrown wrote:
> > On Tue, 20 Nov 2012 09:55:41 -0800 Ross Boylan <ross@biostat.ucsf.edu> wrote:
> > 
> > > While switching the disks a RAID 1 is based on I used the --wait command
> > > to wait for the rebuild to finish.  It returned immediately, but a
> > > subsequent query showed it had not been rebuilt.  Have I misunderstood
> > > something, or is this an error?
> > > 
> > > While doing these commands a much larger rebuild was going on with a
> > > different array, involving some of the same physical disks but different
> > > partitions.  The partitions being rebuilt are on different physical
> > > disks for the different arrays.
> > > 
> > > Here are the logs, with version info at the end (Debian Lenny + more
> > > recent kernel):
> > ....
> > 
> > > markov:~# uname -a
> > > Linux markov 2.6.32-5-amd64 #1 SMP Wed Jan 12 03:40:32 UTC 2011 x86_64 GNU/Linux
> > > markov:~# mdadm --version
> > > mdadm - v2.6.7.2 - 14th November 2008
> > > 
> > > 
> > > I notice that in this case, unlike the other array, the message during
> > > the rebuild (the last detail report) does not include a line like
> > > Rebuild Status : 0% complete
> > > 
> > > I just tried --wait again to see if there was some kind of race, but
> > > once again it returned immediately, though detail says the spare is
> > > rebuilding.
> > 
> > Can you test this patch to see if it fixes the problem?
> > 
> > diff --git a/Monitor.c b/Monitor.c
> > index c4d57c3..a5e7aaa 100644
> > --- a/Monitor.c
> > +++ b/Monitor.c
> > @@ -973,7 +973,7 @@ int Wait(char *dev)
> >  			if (e->devnum == devnum)
> >  				break;
> >  
> > -		if (!e || e->percent < 0) {
> > +		if (!e || e->percent == RESYNC_NONE) {
> >  			if (e && e->metadata_version &&
> >  			    strncmp(e->metadata_version, "external:", 9) == 0) {
> >  				if (is_subarray(&e->metadata_version[9]))
> > 
> > 
> > NeilBrown
> My source for 2.6.7.2 looks somewhat different.  It only has 627 lines;
> I think this is the relevant code (at the end of the file):
> /* Not really Monitor but ... */
> int Wait(char *dev)
> {
>         struct stat stb;
>         int devnum;
>         int rv = 1;
> 
>         if (stat(dev, &stb) != 0) {
>                 fprintf(stderr, Name ": Cannot find %s: %s\n", dev,
>                         strerror(errno));
>                 return 2;
>         }
>         if (major(stb.st_rdev) == MD_MAJOR)
>                 devnum = minor(stb.st_rdev);
>         else
>                 devnum = -1-(minor(stb.st_rdev)/64);
> 
>         while(1) {
>                 struct mdstat_ent *ms = mdstat_read(1, 0);
>                 struct mdstat_ent *e;
> 
>                 for (e=ms ; e; e=e->next)
>                         if (e->devnum == devnum)
>                                 break;
> 
>                 if (!e || e->percent < 0) {
>                         free_mdstat(ms);
>                         return rv;
>                 }
>                 free(ms);
>                 rv = 0;
>                 mdstat_wait(5);
>         }
> }
> 
> 
> The section
>                 if (!e || e->percent < 0) {
>                         free_mdstat(ms);
>                         return rv;
>  is the only one with e->percent < 0.  Is it OK to change that to 
> if (!e || e->percent == RESYNC_NONE) {?
> 
>

That's the right place to make the change, bit it won't compile.
RESYNC_NONE isn't defined in that version of mdadm, and you would need to
make some changes in mdstat.c where ent->percent is set.
Current code has


				if (l > 8 && strcmp(w+l-8, "=DELAYED") == 0)
					ent->percent = RESYNC_DELAYED;
				if (l > 8 && strcmp(w+l-8, "=PENDING") == 0)
					ent->percent = RESYNC_PENDING;

which is completely missing from 2.6.7.2.  You'd be a lot better off starting
with 3.2.6 and adding the patch to that.

NeilBrown

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