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Date: Wed, 16 Apr 2008 09:49:39 +0200 From: Seewer Philippe <philippe.seewer@....ch> To: Francis Moreau <francis.moro@...il.com> CC: linux-kernel@...r.kernel.org Subject: Re: Disk geometry from /sys Hi, Francis Moreau wrote: > Hi Seewer, > > On Mon, Apr 14, 2008 at 2:57 PM, Seewer Philippe <philippe.seewer@....ch> wrote: >> As you've problably seen from the other answers, disk geometry is (except >> for a few older devices) unneeded inside the Linux kernel. > > Yes but I'm doing userspace stuff and that's the reason I was asking for the > sysfs thing. > >> I'd say thats the >> reason why there's no sysfs export and I'd further guess disk geometry is an >> artifact most would like to get rid of (or pushed into userspace). >> > > Well, I looked at sfdisk(8) and parted(8) source code and they all need the > geometry description. If I understood correctly the reason why is that it > 'prefers' to align partition sizes/starts on a cylinder boundary because some > bootloaders probably use CHS addressing, but I'm really not sure. Yes indeed, mainly in the (w)intel world though. > >> Anyway, if you really need it, try the patch below. Should apply cleanly to >> version 2.6.23.1 and gives you a geometry/ directory for each block device >> providing the getgeo function. It adds a setgeo counterpart for some >> subsystems as well, allowing 'echo something > ...' so please be careful. >> > > Thanks but I probably won't use it. Using sfdisk, for example, is a > more portable > way to get the geometry from a script. Correct. Though be really careful which geometry you are requesting: root@...al:/# sfdisk -g /dev/sda /dev/sda: 7296 cylinders, 255 heads, 63 sectors/track root@...al:/# sfdisk -G /dev/sda /dev/sda: 116280 cylinders, 16 heads, 63 sectors/track The first one is the kernels idea of a disks geometry which is probably as often correct as it's just plain wrong, versus the second one which tries to guess a disks geometry by looking at the current partition table. Which might be just as wrong since its only necessary for bios and/or bootloader. Really depends on what you need. Cheers Philippe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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