Date: Tue, 22 Aug 1995 12:33:06 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, msmith@atrad.adelaide.edu.au Cc: freebsd-hackers@FreeBSD.org, roberto@keltia.frmug.fr.net, terry@cs.weber.edu Subject: Re: Install issues (was: State of the union speech Message-ID: <199508220233.MAA19187@godzilla.zeta.org.au>
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>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 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). >what I can of the diskslice code and the like, but I'm at a loss as to >how to redirect a slice to point at this slab, short of rewriting >the partition table (which would be Bad) or writing a variant on the >vnode driver (which would defeat the whole purpose). 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. >This is basically a ready-to-go partition, it just needs water, so to speak. 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. Bruce
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