Date: Fri, 26 Jul 1996 14:43:37 -0400 From: Garrett Wollman <wollman@lcs.mit.edu> To: Joe Greco <jgreco@brasil.moneng.mei.com> Cc: imp@village.org (Warner Losh), jkh@time.cdrom.com, freebsd-current@freebsd.org Subject: Re: cvs commit: src/sys/dev/ccd ccd.c src/sys/dev/vn vn.c src/sys/sys conf.h src/sys/i386/isa fd.c mcd.c scd.c wcd.c wd.c wt.c s Message-ID: <9607261843.AA05293@halloran-eldar.lcs.mit.edu> In-Reply-To: <199607261830.NAA17041@brasil.moneng.mei.com> References: <199607261727.LAA28387@rover.village.org> <199607261830.NAA17041@brasil.moneng.mei.com>
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<<On Fri, 26 Jul 1996 13:30:33 -0500 (CDT), Joe Greco <jgreco@brasil.moneng.mei.com> said: > I don't have anything useful to suggest other than to note that Sun took the > easy way out of this problem by implementing a "devfs-on-ufs", i.e. they use > UFS and have a procedure for "automatically" creating new instances of > devices. Well, perhaps this is an indication of the correct way to implement persistence. Filesystems keep device nodes as they currently exist, but they don't actually do anything---they are just place-holders that return ENXIO or some such if you try to do anything to them. However, if a devfs layer is stacked on top of a directory containing such a node, then the devfs hides any device nodes that are not available in the running system, and ``adopts'' the permissions of the underlying nodes for its own local devices. That way, upgrading an old system to devfs would Just Work. Attempts to change the permissions of a node would cause a new node to be created in the underlying filesystem, and the permissions changed on that, as well. This fixes the persistence problem, leverages our stackable filesystem infrastructure in a useful way, and makes devices work again over NFS. (This wouldn't support renaming of devices, but I don't know if that's at all useful if we have symbolic links instead.) Julian, does this sound reasonable to you? -GAWollman -- Garrett A. Wollman | O Siem / We are all family / O Siem / We're all the same wollman@lcs.mit.edu | O Siem / The fires of freedom Opinions not those of| Dance in the burning flame MIT, LCS, ANA, or NSA| - Susan Aglukark and Chad Irschick
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