Re: ipc64_perm - generic

Re: ipc64_perm - generic

[Arnd Bergmann]

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 <><

Re: ipc64_perm - generic

[Michal Simek]

Arnd Bergmann wrote:
> 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.

Is it this final solution (that above) or we just change kernel_mode_t to short?

Michal





> 
> 	Arnd <><


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Michal Simek, Ing. (M.Eng)
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