What to do when size of the struct differs on 32 and 64 bit?

[Marcus Meissner]

On Tue, Aug 12, 2008 at 11:44:20PM -0600, Vitaliy Margolen wrote:
> While debugging some force-feedback issues ran into an interesting problem. 
> The size of one struct from include/linux differs between 32-bit and 64-bit. 
> That wouldn't be a major problem except that size is the part of the ioctl() 
> request. Which results in EINVAL.
> 
> In more details:
> input.h:
> #define EVIOCSFF _IOC(_IOC_WRITE, 'E', 0x80, sizeof(struct ff_effect))
> 
> The simple test program:
> 
> #include <linux/input.h>
> #include <stdio.h>
> int main(int argc, char * argv[])
> {
>      printf("sizeof(struct ff_effect) = %d EVIOCSFF=%#x\n", sizeof(struct 
> ff_effect), EVIOCSFF);
> 
>      return 0;
> }
> 
> 
> $ gcc test_size.c -o test_size && ./test_size
> sizeof(struct ff_effect) = 48 EVIOCSFF=0x40304580
> $ gcc -m32 test_size.c -o test_size32 && ./test_size32
> sizeof(struct ff_effect) = 44 EVIOCSFF=0x402c4580
> 
> The question is what do we do about it? I'm sure there are might be more 
> cases like that.

The kernel is supposed to handle this transparently.

I would report this to the kernel developers, mention "32bit compatibility"
or so.

Ciao, Marcus