From owner-freebsd-current@FreeBSD.ORG Wed Nov 30 15:55:11 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D66F01065673; Wed, 30 Nov 2011 15:55:11 +0000 (UTC) (envelope-from mlfbsd@kanar.ci0.org) Received: from kanar.ci0.org (unknown [IPv6:2a01:e0b:1:50:40:63ff:feea:93a]) by mx1.freebsd.org (Postfix) with ESMTP id 65CF78FC19; Wed, 30 Nov 2011 15:55:11 +0000 (UTC) Received: from kanar.ci0.org (pluxor@localhost [127.0.0.1]) by kanar.ci0.org (8.14.2/8.14.3) with ESMTP id pAUFtLZv053095; Wed, 30 Nov 2011 16:55:21 +0100 (CET) (envelope-from mlfbsd@kanar.ci0.org) Received: (from mlfbsd@localhost) by kanar.ci0.org (8.14.2/8.14.3/Submit) id pAUFtLG4053094; Wed, 30 Nov 2011 16:55:21 +0100 (CET) (envelope-from mlfbsd) Date: Wed, 30 Nov 2011 16:55:21 +0100 From: Olivier Houchard To: Kostik Belousov Message-ID: <20111130155521.GA52567@ci0.org> References: <20111130124320.GA1449@azathoth.lan> <201111301005.11938.jhb@freebsd.org> <20111130154636.GX50300@deviant.kiev.zoral.com.ua> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111130154636.GX50300@deviant.kiev.zoral.com.ua> User-Agent: Mutt/1.4.2.1i X-Mailman-Approved-At: Wed, 30 Nov 2011 16:35:53 +0000 Cc: Baptiste Daroussin , freebsd-current@freebsd.org Subject: Re: [patch] turning devctl into a "multiple openable" device X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 Nov 2011 15:55:12 -0000 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