Date: Sat, 9 Aug 2008 11:27:58 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Peter Jeremy <peterjeremy@optushome.com.au> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, Ed Schouten <ed@freebsd.org>, cvs-all@freebsd.org, John Baldwin <jhb@freebsd.org> Subject: Re: cvs commit: src/sys/dev/io iodev.c Message-ID: <alpine.BSF.1.10.0808091127170.36489@fledge.watson.org> In-Reply-To: <20080809001256.GL64458@server.vk2pj.dyndns.org> References: <200808081343.m78DhwYE068477@repoman.freebsd.org> <200808081226.32089.jhb@freebsd.org> <20080809001256.GL64458@server.vk2pj.dyndns.org>
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On Sat, 9 Aug 2008, Peter Jeremy wrote: > On 2008-Aug-08 12:26:31 -0400, John Baldwin <jhb@freebsd.org> wrote: >> It should be setting D_TRACKCLOSE though so that close() reliably clears >> the flag even in single-threaded processes. You can still get odd behavior >> if you explicitly open it twice in an app and then close one of the two >> fd's. You will no longer have IO permission even though you still have one >> fd open. However, if you do that I think you deserve what you asked for. :) > > That behaviour may be legitimate: Your code links with libraries foo and > bar that each independently open /dev/io so they can frob different things > in IO space. libfoo needs ongoing access to device foo and so keeps its > descriptor open. libbar only needs once-off access to device bar and so > closes /dev/io once it's finished its initialisation. Libraries foo and bar > are completely independent and shouldn't need to know anything about each > other and your app shouldn't need to know that libraries it's using frob > around in IO space. If that's the view, there should probably be a per-process counter, although this is all a bit tricky anyway since file descriptors and processes have a tenuous relationship. Robert N M Watson Computer Laboratory University of Cambridge
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