[ENBD] md5sum switch

[Peter T. Breuer]

"Also sprach Arne Wiebalck:"
> you're coding a switch into the threshold value, which is a nice
> idea. but wouldn't it be easier to use a central flag and leave the rest
> as it is? I think that one would understand the meanings of

Oh - I see, that is what you mean by sysctls! :- you want to add something
into systune.conf to control the characteristics at bootup.

> dev.enbd.md5_off_threshold = 10
> dev.enbd.md5_on_threshold = 1000 and
> dev.enbd.md5sum = 0

> without a man page. if you implement your proposal,
> you definitively must write some sentences in the man page ... :-)

Indeed, if one wants to use the /proc/sys/dev/enbd interface, then I
think one has to do it as you suggest, because I cannot 
trigger actions when a change is made there.  They'd have to be tested
all the time.

The only problem with that /proc/sys/dev interface is that it is all
"per driver" and not "per device".  I think I meant to make these things
controllable per device, and putting things into /proc/sys/dev makes
that harder to eventually change.

Peter