Date: Mon, 8 Jan 1996 13:17:18 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: bde@zeta.org.au (Bruce Evans) Cc: msmith@atrad.adelaide.edu.au, phk@critter.tfs.com, hackers@FreeBSD.org Subject: Re: Add new slice to running system, comments? Message-ID: <199601082017.NAA10301@phaeton.artisoft.com> In-Reply-To: <199601080918.UAA19835@godzilla.zeta.org.au> from "Bruce Evans" at Jan 8, 96 08:18:35 pm
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> Slices are supposed to be disjoint. There are enough complications for > overlapping partitions inside slices. Since the windows swap file is in > a DOS slice, it seems best to create a label for this slice and describe > the swap file as the b partition in the label. You will need a label > anyway since swapping only works on the b partition. > > The DIOCSDINFO ioctl can be used to set an in-core label without writing > it to the disk. You can experiment with this by removing the disk > write(s) from `disklabel -r'. It seems to me that the disjoint nature of slices points to an initial (but necessary in a pre-devfs era) design limitation inherent is using a slice-like abstraction. Now that "devfs is here", it should be possible to put the slice management (really logical device management) into devioctl's that operate on the logical device instances. This relies on the ability to stack or collapse lists of logical devices into a physical device reference, offset, and size. The limitation on collapse (forcing a rereference and thus a potential relocation translation) would apply when mapping a logical device to a logical device that does media perfection and thus can not be collapsed (collapse applies only to linear addressing models). This "magically" allows disklabels and second stage boot code to take advantage of sector forwarding (currently, this is limited to formal slices in the BSD code). It also gives a handly place to hook volume spanning drivers, like those used for concatenation, striping, and/or RAID. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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