On Monday 25 May 2009 18:54:42 Michal Simek wrote:
>
> Hi Arnd, cc: John
>
> From asm-generic/posix_types.h
>
> 17 #ifndef __kernel_mode_t
> 18 typedef unsigned int __kernel_mode_t;
> 19 #endif
>
> This structure is not aligned properly because of pad2.
>
> 19 struct ipc64_perm {
> 20 __kernel_key_t key;
> 21 __kernel_uid32_t uid;
> 22 __kernel_gid32_t gid;
> 23 __kernel_uid32_t cuid;
> 24 __kernel_gid32_t cgid;
> 25 __kernel_mode_t mode;
> 26 unsigned short __pad1;
> 27 unsigned short seq;
> 28 unsigned short __pad2;
> 29 unsigned long __unused1;
> 30 unsigned long __unused2;
> 31 };
>
> I think we should remove __pad1.
> What do you think?
Right, well spotted.
I'd like to keep the struct ipc64_perm compatible with most architectures, so
maybe we can play a little trick here:
> Here is proposed struct.
> struct ipc64_perm {
> __kernel_key_t key;
> __kernel_uid32_t uid;
> __kernel_gid32_t gid;
> __kernel_uid32_t cuid;
> __kernel_gid32_t cgid;
> __kernel_mode_t mode;
+ unsigned char __pad1[4 - sizeof(__kernel_mode_t)];
> unsigned short seq;
> unsigned short __pad2;
> unsigned long __unused1;
> unsigned long __unused2;
> };
If that's too much of a hack, we could also change the default __kernel_mode_t
in asm-generic/posix_types.h to unsigned short, which it is on all 32-bit architectures
except mips and xtensa. For some reason, all 64 bit architechtures use unsigned
int for mode_t, but I couldn't find out why. Glibc uses unsigned int externally.
Arnd <><
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