Comment # 2 on bug 1068707 from Coly Li

(In reply to Coly Li from comment #1)
> (In reply to Ruediger Oertel from comment #0)
> > trying to repeat on s390x what worked on aarch64 ...
> > 
> > OBS_WORKER_DISK=/dev/mapper/3600a098051764b2d515d436d66416b4f
> > wipefs -f -a $OBS_WORKER_DISK
> > modprobe zram num_devices=1
> > modprobe bcache
> > echo 8G > /sys/block/zram0/disksize
> > wipefs -f -a /dev/zram0
> > make-bcache --wipe-bcache --block 4k --bucket 2M -B $OBS_WORKER_DISK -C
> > /dev/zram0
> > # up to here it seemed to work, but:
> > echo /dev/zram0 > /sys/fs/bcache/register
> > -bash: echo: write error: Invalid argument
> > 
> > in dmesg:
> > [1256250.924470] zram: Added device: zram0
> > [1256258.363017] zram0: detected capacity change from 0 to 8589934592
> > [1256269.146000] bcache: register_bcache() error opening /dev/dm-2: Not a
> > bcache superblock
> > [1256275.462897] bcache: register_bcache() error opening /dev/zram0: Not a
> > bcache superblock
> > 
> > so the written superblock is not recognized ... endianess issue ?
> 
> It is very probably an endianess issue. Good to know people use bcache on
> non-little-endian machines. Hmm, I need to find a 390x machine to fix and
> test the code ...
> 
> Thanks for the report.

The problem is not from kernel, it is from make-bcache tool. The user space
tool does not use xx_to_cpu() and cpu_to_xx() family so all super block values
are in little endian.

I will post a patch for testing.

Coly