Messages in this thread | | | Date | Fri, 18 Dec 2009 12:10:39 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 1/9] x86: move range related operation to one file |
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On 12/18/2009 01:46 AM, Yinghai Lu wrote: > + > +struct range { > + u64 start; > + u64 end; > +};
Okay, this does bring up two things that I have long griped about.
Firstly, I don't think this is the proper data structure. Even worse, the range operations take *inclusive* ranges (e.g. 0x0000 to 0xffff is 64K, not 0x0000 to 0x10000). It would be one thing if it only affected the internal representation, but as written, this is exposed through the interfaces, too.
As far as the choice of data structures, I have used in other places, with very good success, a data structure which looks like:
struct { u64 start; u32 attr; };
Note that there is no end: the end is always given by an end token. The "attr" here was an e820 attribute (or 0 for no attribute), but the payload can be almost anything -- for a simple include/exclude it can just be boolean.
This data structures doesn't permit things like out-of-order ranges, overlapping ranges, and so on, and that's a good thing; it means the data structure itself can never be ambiguous, and the interfaces clean out most errors inherently.
http://git.kernel.org/?p=boot/syslinux/syslinux.git;a=blob;f=com32/lib/syslinux/zonelist.c;hb=HEAD
... contains an implementation of this data structure using linked lists for internal storage, and
http://git.kernel.org/?p=boot/syslinux/syslinux.git;a=blob;f=memdisk/e820func.c;hb=HEAD
... contains one based on arrays. I'm not saying these should be applied directly, but I think the equivalent concept might be worthwhile, not just for this but also for the e820 memrange code.
-hpa
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