Re: return negative number for unsigned long function in kernel

[Andreas Schwab <schwab@suse.de>]

"Chen, Dongliang" <Chen.D@ems-t.com> writes:

> 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? 

The return value is directly passed to user space (it's the guts of the
mmap syscall).  The glibc wrapper transforms it appropriately so that
errno is set and -1 is returned if there is an error.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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