[dm-devel] [RFC] Some fixes to allow for more than 128 md devices.

[Robert LeBlanc]

Apparently, the mdadm source on git-kernel.org (commit 13db17bd)
already has the fixes to properly create the device nodes, but I still
have the unexpected failure opening /dev/md1048574.
----------------
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1


On Fri, Aug 19, 2016 at 8:10 PM, Robert LeBlanc <robert at leblancnet.us> wrote:
> I'm stuck and need some help getting this across the finish line. This
> is in no way complete, but to help show what I'm working on.
>
> When we added more than 128 md devices, we started getting failures.
> Looking through the code it seems that the minor dev number was being
> stored in an int and causing overflow and wrecking havoc on everything.
> I finally got the mknod in mdadm to correctly make the dev node with
> minors up to 1048574 as expected in the mdadm code. However, I can
> only create md devices up to 511. Trying to create an md higher than
> that has an error where the device can't be read/opened strace reports:
> open("/dev/.tmp.md.15341:9:1048574", O_RDWR|O_EXCL|O_DIRECT) = -1 ENXIO
> (No such device or address)
> while Python reports:
> IOError: [Errno 6] No such device or address: '/dev/.tmp.md.3279:9:512'
>
> A corresponding node is not created in /sys/block/md* for mds over 511.
>
> I believe that there may be a bug in the kernel code that is now being
> hit. After looking through the kernel code, I can't seem to find where
> this might be. Please help me by either pointing me to the source
> location that this might be a problem or fixing it based on these
> patches I've worked on so far. I'm using 4.7.0 currently.
>
> I'm using this for testing:
> ./mdadm --create /dev/md1048574 --assume-clean --verbose --level=1 \
> --raid-devices=2 /dev/loop0 missing
>
> Yes, we have a real need for more than 128 and 512 md devices.
>
> Please include me in any replies as I'm not on the ML.
>
> Thank you.
>
> Robert LeBlanc (1):
>   Some fixes to allow for more than 128 md devices.
>
>  Manage.c |  5 +++--
>  lib.c    |  2 +-
>  mdadm.h  |  6 +++---
>  util.c   | 25 +++++++++++++------------
>  4 files changed, 20 insertions(+), 18 deletions(-)
>
> --
> 2.8.1
>