mention msleep() in porting_drivers.txt

[Matthew Dillon]

:Agreed. The reason I didn't just add an example for MTX_SPIN mutexes is
:precisely not to encourage just blindly copying FreeBSD's fine-grained
:locking. Explaining alternative strategies and tradeoffs would require
:a seperate article of its own though.
:
:Aggelos

    Yah, I far prefer that people use lockmgr locks for most porting from
    FreeBSD, if only to make debugging far, far easier.  They aren't half
    bad... over the years I've removed a lot of cruft from the lockmgr API,
    it's actually pretty efficient.

    The interrupt serializer is the best locking mechanism to use for drivers
    which have interrupt service routines, but requires a bit more research
    to use properly in a port vs lockmgr locks.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>