[PATCH] linux: Fix integer overflow warnings when including <sys/mount.h> [BZ #32708]

[Florian Weimer]

* Collin Funk:

> Florian Weimer <fweimer@redhat.com> writes:
>
>> This change alters the type of all enum constants from int to unsigned
>> int.  Should we keep the type of the other constants?  Or use INT_MIN
>> (expanded) for MS_NOUSER?
>
> Since mount(2) expects an unsigned long flags, I feel like changing it
> to unsigned should be fine. Since the flags are meant to be OR'd
> together, I don't think anyone should be using operators like ==, which
> might trigger -Wsign-compare or something like that.

I'm not sure if there are any good options here.

The type unsigned long is clearly nominal only, the kernel has to
disregard the upper 32 bits if they exist due to the current sign
extension.

I looked at previous examples, and we generally use 1U << 31 instead of
-2147483647 - 1.  This commit made all enum constants unsigned, too:

commit 4920765eb417431261367bf65f1a8a5ffb78baf7
Author: Ulrich Drepper <drepper@gmail.com>
Date:   Wed Dec 21 22:14:05 2011 -0500

    Define EPOLLONESHOT and EPOLLET using unsigned values

So there is some precedent for what you are doing here.

I believe unsigned enum types are still a GNU extension, but maybe
<sys/mount.h> isn't expected to be processed with compilers without such
extensions.

Thanks,
Florian