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SubjectRe: [stable] Ioctl in change the argument value?

On Wed, Jun 29, 2011 at 11:09:26PM -0700, ????????? wrote:
> Hello everybody,
> When I want to get the block size about the block device(DM or real),I
> use the system API like "ioctl(int fd, BLKGETSIZE,long size)".
> Everything works fine. But when I pass the third parameter whose type
> is "int", the first parameter fd will be changed to zero. It only
> happened on x86_64 and 2.6.35 ,on 2.6.38 and 32bit will not occur,
> I've already tested on them.
> (My PC:Linux server-group 2.6.35-22-server #33-Ubuntu SMP Sun Sep 19
> 20:48:58 UTC 2010 x86_64 GNU/Linux)
> here is the test code:
> int main(){
> int fd;
> int blksize ;
> fd = open("/dev/sda",O_RDONLY,0);
> ioctl(fd, BLKGETSIZE,&blksize) ;
> close(fd);
> }
> If I change the fd type as long( int fd ==> long fd ) , won't occur
> again. I quite sure the ioctl syscall when return to userspace changes
> the fd's value.

This is expected, check the ioctl list (man ioctl_list) :
0x00001260 BLKGETSIZE unsigned long *

So it returns a long, and you need to have blksize declared as long
and not as int. On 32-bit systems, both are the same size so your
bug has no effect.

Please also note that this is irrelevant to the stable list.


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