Date: Tue, 25 Jan 2005 17:01:27 +0000 (GMT) From: Robert Watson <rwatson@freebsd.org> To: Warner Losh <imp@rover.village.org> Cc: imp@bsdimp.com Subject: Re: Devd event from GEOM? Message-ID: <Pine.NEB.3.96L.1050125165810.3036G-100000@fledge.watson.org> In-Reply-To: <20050125.095019.71141844.imp@harmony.village.org>
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On Tue, 25 Jan 2005, Warner Losh wrote: > > each abstraction layer can declare the events it knows about. newbus > > announces "I found a route to a physical device", GEOM shouts "And I found > > some storage space on it", etc. > > Actually, GEOM will announce all the layers as well, since it is an > onion sort of thing. For the degenerate case of FAT on FLASH Stick, it > is easy, because you don't see the layers. But I routinely plug in CF > cards that have FreeBSD file systems on them, as well as an emergency > DOS partition. Those sort of cases make whatever automounting daemon > need to grow a lot of brains, and will have multiple events. A simple auto-mounter simply watches for every storage device that arrives via GEOM, checks to see if it's leaf class, and if it is, tastes for a file system header, auto-detecting some of the simple and common types, such as FAT, UFS, UFS2, cd9660. It can then use whatever logic it pleases, probably partly from a config file, to decide where to mount it, what security parameters to use, etc. Here-in lies the key: because devd says "a storage device, /dev/ad0s1a arrived", it knows it can just go ahead and taste, not worrying about rewinding the tape, reading from kernel memory, etc. The auto-mounter specifically wants to hear only about GEOMs. Robert N M Watson
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