CAM locking

[Scott Long]

Hidetoshi Shimokawa wrote:
> Hi Scott,
> 
> Thank you for your work on CAM.
> I have some questions about lock assertion.
> 
> 1. Now, xpt_done() should be called with a sim lock for QUEUED ccbs.
>    Why don't you add an assertion in xpt_done()?

Accessing the sim_lock from the CCB requires enough dereferences that if
the lock isn't already held, you'll probably run into problems just
doing the derefs in the assertion.  Adding a sim_lock field to the CCB
has crossed my mind, but I don't want to pollute the CCB with more
kernel-only fields if I can.  I need to think some more on it.

> 
> 2. CAMDEBUG seems useless with WITNESS because xpt_path_path_id() requires
>    a sim lock. Can we safely drop the assertion?

Yes, this is an area that I didn't clean up very well.  A lot of code in
periphs and SIMs wants to be able to use CAMDEBUG functions in random
places without the lock held, and I don't know of a good way to safely
fix this without rewriting a lot of code.  I don't know if it's better
to just drop the assertion or to audit all of the code provide locked
and unlocked versions of the CAMDEBUG functions.

Scott