[9fans] DMEXCL vs. QTEXCL

[9fans] DMEXCL vs. QTEXCL

[Lyndon Nerenberg (VE6BBM/VE7TFX)]

Given the overlap between (DM|QT)EXCL, it's not clear to me which
of these is considered the authority for indicating exclusive access.

devusb.c plays with DMEXCL, devcons.c with QTEXCL.  I'm assumed the
DMEXCL bit was magically getting propagated down to QTEXCL in
qid.type, but I'll be damned if I can find anything in the kernel that
actually does anything with either of these bits.  WTF am I missing?
This should be stunningly obvious.  Someone please stun me more than I
am :-P

My interest is in the context of `Chan's.

--lyndon

Re: [9fans] DMEXCL vs. QTEXCL

[C H Forsyth]

Qid.type == mode>>24, and since they should agree, they have equal authority.
it's the file server or the device driver that ensures equality.
dev.c:/^devdir\( does so for many device drivers, based on the type value of the incoming Qid.

it looks like a mistake that devusb.c doesn't set QTEXCL in Qid.type when the mode requires it,
but perhaps devdir should also merge the bits both ways (ie, set qid.type |= mode>>24 as well
as db->mode |= qid.type<<24)