Re: mdadm --detail works, mdadm --stop says "does not appear to be an md device"

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Mon, 20 Mar 2023 07:50:35 -0700
Marc MERLIN <marc@merlins.org> wrote:

> On Mon, Mar 20, 2023 at 03:36:39PM +0100, Mariusz Tkaczyk wrote:
> > Hi,
> > mdadm is unable to complete this task because it cannot ensure that it is
> > safe to stop the array. It cannot open the array with O_EXCL.
> > If it is mounted then it may hang if filesystem needs to flush some data.  
>  
> Thanks for the reply. The array was not mounted, that said, given that
> it was fully down, there wasn't a way to flush the data if it had been
> (cable problem to an enclosure, all the drives disappeared at once)
> 
> > Please, try umount the array if it mounted somewhere and then try:
> > 
> > # echo inactive > /sys/block/md6/md/array_state
> > # echo clear > /sys/block/md6/md/array_state  
> 
> I can try this next time (already had to reboot), thanks.
> 
> That said, mdadm should output a better message in this case
> > > mdadm: /dev/md6 does not appear to be an md device  
> is clearly wrong 
> 
> Is that something easy to fix/improve?

Oh, sorry my bad, please see the code:
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/mdopen.c#n472

We are failing to "understand" the array:
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/util.c#n229
It has nothing to do with open and O_EXCL. I didn't dig into to determine why.

Anyway, now error seems to be reasonable but maybe we should be able to tract
this array as valid? I requires more work and analysis so it is not simple fix.

Thanks,
Mariusz