Re: [PATCH 0/1] RFC: Use /dev/md/X as default name

[NeilBrown <neilb@suse.de>]

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On Wed, 18 Feb 2015 17:11:33 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
wrote:

> NeilBrown <neilb@suse.de> writes:
> > On Wed, 18 Feb 2015 13:12:09 -0500 Jes Sorensen <Jes.Sorensen@redhat.com>
> > wrote:
> >
> >> Jes.Sorensen@redhat.com writes:
> >> > From: Jes Sorensen <Jes.Sorensen@redhat.com>
> >> >
> >> > I have received some issues for when creating an array using a
> >> > /dev/mdX name, the matching symlink in /dev/md/X isn't
> >> > created. Whereas if you create /dev/md/X, /dev/mdX is created
> >> > automatically.
> >> >
> >> > I was trying to see if there was a better way of dealing with this,
> >> > but I couldn't find one. If you have suggestions for a better solution
> >> > I am all ears.
> >> >
> >> > Thoughts?
> >> 
> >> Hi Neil,
> >> 
> >> Any thoughts on this one?
> >
> > Thanks for the reminder....
> >
> > I'm not sure that I really see the problem.
> >
> >   "I ask it to create /dev/mdX and it doesn't create /dev/md/X".
> >
> > Well ... no.  You didn't ask it to.  If you want it to create /dev/md/X,
> > then ... ask it to.
> >
> > /dev/mdX is the canonical name.  It always gets created.
> > /dev/md/X is a convenient alias.  It gets created if requested.
> >
> > Is there really a problem here worth solving?
> >
> > Maybe I missed something.
> 
> I have had complaints in Fedora from the installer people that they rely
> on the /dev/md/ name being created when they create a new device. It is
> also inconsistent because /dev/md/<X> will be created if you run
> 'mdadm -As' later on.

If they rely on the /dev/md/ name being created, then surely they should ask
for it to be created.
Is it really harder to run "mdadm -C /dev/md/0" than "mdadm -C /dev/md0" ??

If you create an array as "/dev/md0", then after subsequent "mdadm
-As" /dev/md0 will exist.
If you create an array as "/dev/md/0", then after subsequent mdadm
-As", /dev/md/0 will exist.

The fact that something unasked for also exists is a bonus.

> 
> I don't see it as a major issue, but I can see why it is frustrating for
> some and I think there is something to be said for being consistent in
> behavior.

I think the behaviour is perfectly consistent.  It just follows rules that
are slightly less trivial that some people appear to want.

However....
If you changed

			mp = map_by_uuid(&map, info->uuid);
			if (mp && mp->path &&
			    strncmp(mp->path, "/dev/md/", 8) == 0) {
				printf("MD_DEVNAME=");
				print_escape(mp->path+8);
				putchar('\n');
			}


in Detail.c so that when mp->path were "/dev/md0", MD_DEVNAME became "0",
then you should get the result that you are after, and I probably wouldn't
object to the patch.

NeilBrown 


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