Re: return negative number for unsigned long function in kernel

["H. Peter Anvin" <hpa@zytor.com>]

Chen, Dongliang wrote:
> There are lots of functions in the Linux kernel that are declared as
> unsigned long, but the return value is negative integer while error
> occurred. An example of these functions is do_mmap_pgoff in mm/mmap.c,
> which is defined as:
> 
> unsigned long do_mmap_pgoff(....)
> 
> In this function, it returns -ENODEV, -EPERM, -ENOMEM, -EINVAL, -EAGAIN,
> -EACCESS depends on the error type. My question is how should the caller
> perform error check based on the return value? 
> 

If you want to test for errorness, you could use the macro 
IS_ERR_VALUE().  Unfortunately the macro isn't all that safe, in that it 
will give you the wrong answer if it's ever used on something that 
*isn't* an unsigned long.

	-hpa