RAIDframe: passing component capabilities (was: Exposing FUA as alternative to DIOCCACHESYNC for WAPBL)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

EF> Some comments as I probably count as one of the larger WAPBL consumers 
EF> (we have ~150 employee's Home and Mail on NFS on FFS2+WAPBL on RAIDframe 
EF> on SAS):
JD> I've not changed the code in RF to pass the cache flags, so the patch
JD> doesn't actually enable FUA there. Mainly because disks come and go
JD> and I'm not aware of mechanism to make WAPBL aware of such changes. It
TLS> I ran into this issue with tls-maxphys and got so frustrated I was 
TLS> actually considering simply panicing if a less-capable disk were used 
TLS> to replace a more-capable one.
Oops. What did you do in the end? What does Mr. RAIDframe say?

My (probably simplistic) idea would be to add a capabilities option to the
configuration file, and just as you can't add a disc with insufficient
capacity, you can't add one with insufficient capabilities. Of course,
greater capabilities are to be ignored just as a larger capacity is.