Re: Interesting mdadm quirk ...

[NeilBrown <neilb@suse.com>]

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On Mon, Jan 09 2017, Wols Lists wrote:

> On 08/01/17 22:44, NeilBrown wrote:
>> On Sun, Jan 08 2017, Wols Lists wrote:
>> 
>>> Just been doing some raid testing, and this happened ...
>>>
>>> linux-lfqf:/dev # mdadm md/parity
>>> md/parity: 31.97GiB raid5 3 devices, 0 spares. Use mdadm --detail for
>>> more detail.
>>> linux-lfqf:/dev # mdadm --stop md/parity
>>> mdadm: Cannot open md/parity
>>> linux-lfqf:/dev # mdadm --stop /dev/md/parity
>>> mdadm: stopped /dev/md/parity
>>>
>>> Weird - why can it successfully stop it when passed an absolute path,
>>> but not when passed a relative path? When I did the first variant, I
>>> used tab completion, and then when I edited it I really did edit it, not
>>> retype it, so I can't see any way the two arguments could refer to
>>> different objects.
>> 
>> If you give mdadm a name of an array that start with "/", it is assumed
>> to be a path name (usually in /dev).
>> If it doesn't start with "/", then it is an array name.  The might mean
>> different things in different contexts, I'm not 100% sure.
>> However, for --stop, it a name like you would find is /sys/block or
>> /proc/mdstat.
>> So "mdadm --stop md0" or "mdadm --stop md_parity" might do what you
>> want.
>> Probably the error message could be more useful here.
>> 
> Does that mean an array name can contain a "/"?

No, it cannot.

>
> Assuming it can't, surely it's better to alter the logic slightly...
>
> if char[0] ne '/' then
>   open array_name
> end
> if not successful then
>   open path_name
>   if error then go error_handler
> end
> carry on ...
>
> That way naive users like me won't get a surprise. And it is rather
> inconsistent for it to work with one sort of path but not another ...
> and actually that logic will work fine even if the name does contain a
> "/" :-)

If you can convert the above into a patch.....

I agree with your logic.

NeilBrown

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