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

On Fri, 2006-05-19 at 12:55 -0600, Andreas Dilger wrote:

> 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

%Lu, %Ld, and &Lx are not technically correct, even though the compiler
& printk code allow them.  According to printf(3), "L" refers to a long
double, and "ll" refers to a long long int.

> 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.

I'd rather see a more generic solution.  If defining SECTOR_FMT is the
right thing to do, isn't it likely that the same will be done for a lot
of other types?  On the other hand, it's less intrusive and more
straightforward than anything else we've come up with.

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



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