On Wed, 2010-03-17 at 00:20 +0900, Tejun Heo wrote: > On 03/17/2010 12:02 AM, James Bottomley wrote: > > On Tue, 2010-03-16 at 23:50 +0900, Tejun Heo wrote: > >> e.g. If the first partition begins at CHS 0/32/33 and ends at > >> 12/233/19 and the corresponding LBA addresses are 2048 and 206848, you > >> can solve the equation and determine that the parameters gotta be 63 > >> secs/trk and 255 heads/cyl to make those two pairs of addresses match > >> each other and in fact some BIOSs try to do this depending on > >> configuration (and sometimes falls into infinite loop or causes other > >> boot related problems if the parameters are too uncommon). > > > > for an msdos label, this is illegal, that was Arnd's point. The > > partitions have to begin and end on cylinder boundaries*. Knowing that, > > you can deduce the geometry from the last sector entry. > > > > * at least if you want to preserve windows compatibility, which is what > > most of our partitioning tools seem to do. > > Well, the thing is that > > * Anything remotely modern (>= XP) doesn't give a hoot about cylinder > alignment. > > * Anything older (<= 2000) is very likely to get confused with custom > geometry starting from the BIOS itself. For those cases, the only > thing we can do is aligning partitions to cylinders abiding BIOS > supplied geometry parameters which will usually be 255/63. > > So, using custom geometry doesn't help compatibility at all. Our partitioning tool still obey the integral cylinder rule ... we can argue about whether they should, but what we need is a strategy for fixing what is rather than what should be. James -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
