[dm-devel] How to setup a basic writecache env?

[shenghui]

Hi Mikulas,

Sorry to trouble you.

I recently noticed dm-writecache in the dm dir, and want to have a try.
But I failed to setup a basic writecache dm using dmsetup:

# dmsetup create testwbc --table "0 512000000 writecache s /dev/md1p5 /dev/md1p6 1024"
device-mapper: reload ioctl on testwbc  failed: Invalid argument
Command failed

In dmesg, there is:
[ 7863.034468] device-mapper: table: 253:0: writecache: Invalid number of feature args
[ 7863.034476] device-mapper: ioctl: error adding target to table

I wonder what is the exact args to dmsetup?

Thanks,
shenghui