On Sun, 9 Dec 2001, Linus Torvalds wrote:
> Having in-core data in CPU-native byte order is _stupid_. We used to do
> that, and I winced every time I had to look at all the duplication of
> functions. I think it was early 2.3.x when Ingo did the page cache write
> stuff where I fixed that - the people who had done the original ext2
> endianness patches were just fairly lacking in brains (Hi, Davem ;), and
> didn't realize that keeping inode data in host order was the fundamental
> problem that caused them to have to duplicate all the functions.
>
> So the _wart_ is in 2.2.x, which is just stupid and ugly, and keeps block
> numbers in host data format - which causes no end of trouble. 2.4.x
> doesn't have this problem, and could easily have a pointer to the on-disk
> representation.
As an aside, anybody who uses SWAB... should cut down on drugs.
Code like
native_endian = fs_endian;
if (need_swap)
native_endian = SWAB16(fs_endian);
or, worse yet, same with ifdef instead of if is fscking braindead.
_Never_ treat data from IO as numeric. Incompatible by assignment. If
you have a little-endian data and CPU and your foo_to_cpu() is identity
mapping - fine, but keep that fact in definition of foo_to_cpu().
Endian-neutral code is _easy_ - you need to try real hard to write something
that would be endian-dependent. All you need is to ask yourself "is it
a number or a piece of on-disk data?" and then stick to that. And these
pointers in inode are obvious pieces of on-disk data - no bloody questions
on that.
For real horror look at 2.2 UFS. At least in ext2 DaveM et.al. had enough
sense to use le32_to_cpu() and friends. In UFS it was SWAB...() abortion
all over the place.
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This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:16 EST