Date: Wed, 30 Nov 2011 17:20:17 +0100 From: Olivier Houchard <mlfbsd@kanar.ci0.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: Baptiste Daroussin <bapt@freebsd.org>, freebsd-current@freebsd.org, Olivier Houchard <mlfbsd@kanar.ci0.org> Subject: Re: [patch] turning devctl into a "multiple openable" device Message-ID: <20111130162017.GA53362@ci0.org> In-Reply-To: <20111130160450.GY50300@deviant.kiev.zoral.com.ua> References: <20111130124320.GA1449@azathoth.lan> <201111301005.11938.jhb@freebsd.org> <20111130154636.GX50300@deviant.kiev.zoral.com.ua> <20111130155521.GA52567@ci0.org> <20111130160450.GY50300@deviant.kiev.zoral.com.ua>
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On Wed, Nov 30, 2011 at 06:04:50PM +0200, Kostik Belousov wrote: > > > 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 ? > > > Nothing, but file reference count goes to zero only after the thread > stuck in read is unstuck. Cdevpriv destructor is run only when file > reference count becomes zero, i.e. there can be no any accessing threads, > and new accesses are impossible since file descriptors also own references > on the file. Right, I was a bit confused, this part can be removed. Regards, Olivier
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