Re: [RFC 7/7] ext3 blocks: convert ext3_fsblk_t to sector_t

On May 19, 2006  11:19 -0700, Badari Pulavarty wrote:
> On Fri, 2006-05-19 at 09:42 -0700, Mingming Cao wrote:
> > But checking the rest of 64 bit arch where sector_t is defined, found
> > previous assumption not always true: about on 64 bit machine
> > sector_t/u64 is always unsigned long. At least, cscope shows asm-sh
> > arch, BITS_PER_LONG is 64, while, u64/sector_t is unsigned long long, so
> > this won't work for this case.
> 
> It should work on 64-bit machines also as "long long" is equal to "long"
> (64-bit) on these machines (verified it atleast on x86-64, ppc64)

No, even though the sizes of long and long long are the same on a 64-bit
arch you get compile warnings because this isn't a safe assumption on all
systems.  It is even worse on e.g. x86_64 and SPARC because the types in
userspace aren't the same as in the kernel.  I've had to deal with this for
a long time with Lustre, and we have defined LPU64, LPX64, LPD64 that are
used in all the printks in our code:

#if (defined(__x86_64__) && defined(__KERNEL__))
/* x86_64 defines __u64 as "long" in userspace, but "long long" in the kernel */
# define LPU64 "%Lu"
# define LPD64 "%Ld"
# define LPX64 "%#Lx"
#elif (BITS_PER_LONG == 32 || __WORDSIZE == 32)
# define LPU64 "%Lu"
# define LPD64 "%Ld"
# define LPX64 "%#Lx"
#elif (BITS_PER_LONG == 64 || __WORDSIZE == 64)
# define LPU64 "%lu"
# define LPD64 "%ld"
# define LPX64 "%#lx"
#endif

That said, I think I'd still prefer to have Dave's original SECTOR_FMT patch
since it is completely unambiguous that the format matches the type.  If it
so happens that we get LPU64 into the kernel (which I doubt, since I had
suggested this a long time ago, but maybe things change) then we can
redefine SECTOR_FMT in terms of LPU64.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.



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