Date: Wed, 30 Nov 2011 16:55:21 +0100 From: Olivier Houchard <mlfbsd@kanar.ci0.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: Baptiste Daroussin <bapt@freebsd.org>, freebsd-current@freebsd.org Subject: Re: [patch] turning devctl into a "multiple openable" device Message-ID: <20111130155521.GA52567@ci0.org> In-Reply-To: <20111130154636.GX50300@deviant.kiev.zoral.com.ua> References: <20111130124320.GA1449@azathoth.lan> <201111301005.11938.jhb@freebsd.org> <20111130154636.GX50300@deviant.kiev.zoral.com.ua>
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On Wed, Nov 30, 2011 at 05:46:36PM +0200, Kostik Belousov wrote: > 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. > Queuing the message only one time would require to somehow keep a state, to know which thread read which message, and figuring out when to free a message can be an headache. Given I don't think they'll be a lot of readers, I'm not sure it's worth the trouble. > 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. > What will prevent you from having a thread stuck in read(), while an another one close() the fd ? Regards, Olivier
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