[PATCH] Do not assemble a duplicate of a running array

[Yury Polyanskiy]

Dear Neil,


On Thu, Jul 14, 2011 at 3:30 AM, NeilBrown <neilb at suse.de> wrote:

> I think it is probably much simpler to fix than your attempt.

BTW, I forgot to say that I checked the patch and it works fine of course.

> Something like this:
>
> diff --git a/Assemble.c b/Assemble.c
> index 25cfec1..86b6e95 100644
> --- a/Assemble.c
> +++ b/Assemble.c
> @@ -616,6 +616,17 @@ int Assemble(struct supertype *st, char *mddev,
>        if (!st || !st->sb || !content)
>                return 2;
>
> +       {
> +               int uuid[4];
> +               struct map_ent *mp = NULL;
> +               st->ss->uuid_from_super(st, uuid);
> +               if (map_by_uuid(&mp, uuid)) {
> +                       map_free(mp);
> +                       fprintf(stderr, Name ": Not assembling array as uuid already in use\n");
> +                       return 1;
> +               }
> +               map_free(mp);
> +       }
>        /* Now need to open the array device.  Use create_mddev */
>        if (content == &info)
>                st->ss->getinfo_super(st, content, NULL);
>
>

I thought about checking via mdmap, but decided against it. The check
is so crucial for data integrity that I think it is not a good idea to
introduce dependence on such an unreliable thing as
availability/coherence of mdmap (what if it is stale? Not synchronized
because of readonly root partition?). Much simpler to document and
more robust is to check an UUID on a physical drive, IMHO.

> is what I'm thinking of - it seems to work for me, I'd appreciate it if you
> can confirm that it works for you.
>
> My concern though is that someone might genuinely want to assemble two arrays
> with the same uuid.

Exactly, that's the reason I didn't include it in the Assemble(),
because somebody might want to do something like this, but he will
have to do it manually (--assemble /dev/md1 <drives>). --assemble
--scan should never find two arrays specified via the same UUIDs in
the config file (hence the check for uuid_set).

Let me know what you think,

Yury