lockmgr_sleep() (was Re: ssleep() (was Re: mention msleep() in porting_drivers.txt))

[Simon 'corecode' Schubert]

Aggelos Economopoulos wrote:
On Wednesday 16 January 2008, Simon 'corecode' Schubert wrote:
Aggelos Economopoulos wrote:
So, about adding a lockmgr_sleep(): I think it would be useful; open-coding
the whole thing makes it easy to slip in hard to notice bugs. But what should
the prototype be? If we follow the freebsd semantics, the lock should be re-
acquired on return. This means that we need to do a lockstatus() (which implies
a spin_lock_wr()) to get information that the caller probably has available or
Why?  When we release the lock in lock_sleep, we will obtain the status 
anyways, right?
Assuming you mean lockmgr_sleep() here, no. lockmgr(LK_RELEASE) only returns
0. OTOH nobody in the tree actually checks for that, so we could change
lockmgr to return the lock status in that case. This seems to solve the
problem nicely. Any objections to that?
lockmgr_sleep (or lock_sleep?) knows the internals of a lockmgr lock and 
thus can optimize the access.

The down side of course is having to change a couple of dozen call sites. But
as long as we're breaking people's patches with the name change, we might as
well fix the interface, assuming everyone agrees that's an improvement.
No problem.  We could keep msleep() around for some time.
Maybe for a little bit (and with a big warning to prevent people from using
it; this is a good chance to bring in __attribute__(deprecated)) in order to
avoid breakage for out of tree code, but if we add spin_sleep(), msleep()
has to go. We don't want to end up like freebsd (which has mtx_sleep() AND
msleep()), right? ;)
You mean msleep() has to go after a deprecation period, right?  (period 
being one release cycle = 6 months)

cheers
  simon
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