Date: Tue, 22 Aug 1995 16:20:30 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: bde@zeta.org.au (Bruce Evans) Cc: bde@zeta.org.au, msmith@atrad.adelaide.edu.au, freebsd-hackers@FreeBSD.org, roberto@keltia.frmug.fr.net, terry@cs.weber.edu Subject: Using space in a DOS filesystem Message-ID: <199508220650.QAA25904@genesis.atrad.adelaide.edu.au> In-Reply-To: <199508220233.MAA19187@godzilla.zeta.org.au> from "Bruce Evans" at Aug 22, 95 12:33:06 pm
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Bruce Evans stands accused of saying: > > >Oddly, I haven't had any bites on my last post about this, so I'll ask > >again : I have code that creates a large contiguous slab of sectors in > >an MSDOS filesystem, and hides them under a file. I've explored > > I'm not too keen on this, because of coherency issues (what happens if > the file is deleted while it is in use as a partition or after pointers This is obviously a risk - I'd be inclined to modify the MSDOSFS to make it impossible to remove the file. > to it are set up) and lack of generality (it would be better to optimize > the vn driver for contiguous files; it should be possible to avoid going > through the file system except for initialization). The vn driver is a no-go if we want to boot from this, which is the whole idea. Remember, the aim here is to provide a safer way to plonk a FreeBSD filesystem onto a disk covered in a FAT filesystem. > To test it you could create a slice inside the DOS slice containing the > file. I think fdisk allows bogus things like that. Not recommended. Understood. > The vn driver method already has water :-). Try your file that hides > the sectors as a vn device. It can't hurt to have the sectors contiguous > and performance might be reasonable. I don't think it would be - msdosfs > performance is abysmal and revision 1.16 of vn.c seems to have introduced > doing read/write through the file system except for paging. Will do - as far as I understand, I can't disklabel a vn device, so it's not the final answer... > Bruce -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] My car has "demand start" -Terry Lambert UNIX: live FreeBSD or die! [[
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