linux-kernel - Re: [PATCH v2] posix_types.h: make __NFDBITS compatible with glibc definition

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Message-ID: <CA+55aFwFcWoH=QB5tKgVjWcUH3SLCDVNqJY-oXRYy7AWOJfLPA@mail.gmail.com>
Date:	Tue, 24 Jul 2012 11:46:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, law@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] posix_types.h: make __NFDBITS compatible with glibc definition

On Tue, Jul 24, 2012 at 11:32 AM, Josh Boyer <jwboyer@...hat.com> wrote:
> Recent glibc made a change to suppress sign-conversion warnings from FD_SET
> (glibc commit ceb9e56b3d1).  That patch solved the particular error it was
> aiming to, however applications that #include <linux/types.h> after
> including <sys/select.h> can now hit a build failure if -Werror=sign-compare
> and -D_FORTIFY_SOURCE=2 is passed to gcc.  This can be seen when building
> this trivial application against a recent enough glibc:

Looking more at this, I now hate it for *another* reason.

Making __NFDBITS be a signed value turns __FDELT() and __FDMASK() into
potentially pure and utter crap. Doing signed divisions (or modulus)
is a disaster - suddenly it's not just a bit shift any more.

Guys, the glibc people really seem to not have thought their change
through. Or maybe they fixed their __FDELT/__FDMASK at the same time?

                    Linus
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