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From: Tejun Heo on 16 Mar 2010 11:40 Hello, On 03/17/2010 12:23 AM, James Bottomley wrote: >> 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. The updated ones don't anymore. They just align to 1MiB + whatever the drive requests for offset (the offset-by-one thing). They will basically behave the same as windows vista/7 ones, so it's already fixed. What we can argue is whether adding CHS tricks on top to make those larger alignments somewhat meaningful w/ CHS interpretation too, which I'm objecting on the ground that it doesn't help compatibility at all. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Tejun Heo on 16 Mar 2010 11:50 Hello, On 03/17/2010 12:25 AM, Denys Vlasenko wrote: >> C/H/S of 1023/254/63 is a special marker indicating the value there is >> out-of-range. > > You misunderstood my ^^^ markers. I was trying to highlight > the whole columns of "end head" and "end sector", not the > last partition's 1023/254/63 values. > > In the partition table like shown above it is obvious > that geometry is 255/63. Oh, if you have at least one partition contained under the CHS limit, you can definitely determine the parameters. You need to know two params and there are two equations. You don't even have to consider the alignment. >> We don't have to align to cylinders either. > > If neither the start nor the end is aligned to cylinder's end > and disk has just one partition and it's bigger than 8G, > there is not way to determine geometry. > > If everybody adopts the convention of ending the partitions > at the cylinder end, geometry can be trivially determined by > looking at partition end values. Sans "no of cylinders" value, > which can be easily determined by other means. But this is irrelevant because we don't and can't control everybody. Actually, nobody can. Codes dealing with partition tables have already been out there for a very long time and there's no way to retroactively make them agree on anything. The only reason why we care about CHS values at all is backward compatibility. Going forward, we don't need them at all. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Ric Wheeler on 16 Mar 2010 16:50 On 03/16/2010 11:37 AM, Tejun Heo wrote: > Hello, > > On 03/17/2010 12:23 AM, James Bottomley wrote: > >>> 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. >> > The updated ones don't anymore. They just align to 1MiB + whatever > the drive requests for offset (the offset-by-one thing). They will > basically behave the same as windows vista/7 ones, so it's already > fixed. What we can argue is whether adding CHS tricks on top to make > those larger alignments somewhat meaningful w/ CHS interpretation too, > which I'm objecting on the ground that it doesn't help compatibility > at all. > > Thanks. > > Dropping any mention of CHS seems to be the only sensible thing. Why waste any time to continue some myth about drives that no modern hardware supports (and then have the joy of explaining that to users)? Talking about it only confuses people and in the worst case, could cause them to misalign their partitions by clinging to these pretend borders :-) ric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: H. Peter Anvin on 16 Mar 2010 19:50 The only reason I see to care about CHS at all is that there are systems in the field which can only boot from USB in CHS mode, and which often look at the MBR partition table to guess the geometry. Of course, some then *report* the detected geometry but don't *use* the detected geometry... "Ric Wheeler" <rwheeler(a)redhat.com> wrote: >On 03/16/2010 11:37 AM, Tejun Heo wrote: >> Hello, >> >> On 03/17/2010 12:23 AM, James Bottomley wrote: >> >>>> 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. >>> >> The updated ones don't anymore. They just align to 1MiB + whatever >> the drive requests for offset (the offset-by-one thing). They will >> basically behave the same as windows vista/7 ones, so it's already >> fixed. What we can argue is whether adding CHS tricks on top to make >> those larger alignments somewhat meaningful w/ CHS interpretation too, >> which I'm objecting on the ground that it doesn't help compatibility >> at all. >> >> Thanks. >> >> > >Dropping any mention of CHS seems to be the only sensible thing. Why >waste any time to continue some myth about drives that no modern >hardware supports (and then have the joy of explaining that to users)? > >Talking about it only confuses people and in the worst case, could cause >them to misalign their partitions by clinging to these pretend borders :-) > >ric > -- Sent from my mobile phone, pardon any lack of formatting.
From: Tejun Heo on 16 Mar 2010 22:10
Hello, Ric. On 03/17/2010 05:42 AM, Ric Wheeler wrote: > Dropping any mention of CHS seems to be the only sensible thing. Why > waste any time to continue some myth about drives that no modern > hardware supports (and then have the joy of explaining that to users)? > > Talking about it only confuses people and in the worst case, could cause > them to misalign their partitions by clinging to these pretend borders :-) I don't think not mentioning it would clear up the myth. It would probably be a good idea to beef up the document to clear misconceptions around disk geometry. I'll give a shot at it. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |