On Wed, Nov 30, 2011 at 10:05:11AM -0500, John Baldwin wrote: > On Wednesday, November 30, 2011 7:43:20 am Baptiste Daroussin wrote: > > Hi all, > > > > With the help of cognet, I wrote a patch to turn devctl into a multiple > > openable > > device, that mean that it will allow to open /dev/devctl in multiple > > programs, > > for example hald and everythings that want to receive notification from the > > device won't need to depend on haveing devd running. > > > > here is the patch: > > http://people.freebsd.org/~bapt/devctl_multi_open.diff > > Shouldn't devctl_queue_data_f() use the requested malloc() flags instead of > hardcoding M_NOWAIT? This is an obvious fallback of holding mutex around the call to per_devctl_queue_data_f(), which caused the author a trouble to use M_WAITOK.
Having n readers causes the patch to queue each message n times, that looks like a waste. I wonder why the waiting_threads stuff is needed at all. The cv could be woken up unconditionally everytime. What is the reason for the cv_wait call in cdevpriv data destructor ? You cannot have a thread doing e.g. read on the file descriptor while destructor is run. > > Also, I know that it was an intentional design decisison by Warner to have > the multiplexing of devctl data done in userland via devd rather than in the > kernel. (I think he envisioned devd providing a UNIX domain socket or some > such for other daemons to use to listen to events.) Have you asked him about > this change? And I fully agree that doing multiplexing in user mode is the right approach. Not least because you could apply some advanced access control and provide filtering for the consumers.
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