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

[Robert LeBlanc]

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(-)

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2.8.1