[dm-devel] Bug? Determining the holders of partitions shadowed by dm-multipath.

[Hannes Reinecke]

Hi Joel,

Joel Becker wrote:
> On Tue, Feb 10, 2009 at 09:49:58AM -0500, Romanowski, John (OFT) wrote:
>> my sles10sp2 at 2.6.16.60-0.29-default doesn't have the /sys/block/.../holders but
>> I've used major:minor device numbers from commands
>> dmsetup ls
>> and
>> dmsetup deps
>> to resolve such device relationships.
>>
>> A 'dmsetup ls' device number that isn't listed in 'dmsetup deps' device numbers is a top-level device. Example below: mproot-part1 (dev 253:3, a partition of mp device 253:2) isn't listed as a dependency of any device. Likewise each listed LVM volume isn't listed as a dependency of any device; example- rootvg-tmp 253:10
> 
> 	Sure, but a /dev/sda2 won't show up in dmsetup output anywhere.
> That's kind of my point.
> 
Well, yes.
That's because you have _two_ parent-child relationship in sysfs.

The one (as you already noted) is the holders / slaves directories in sysfs.
However, partitions are handled differently; they are listed under

/sys/block/sda/sda2

(note the subdir) and do not appear under holders / slaves. So the correct algorithm
is to
a) check the holders / slaves 
and
b) check if the parent directory starts with the same name and if so, check for
the holders / slaves relationship there.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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