Re: [glibc PATCH] fcntl: put F_OFD_* constants under #ifdef __USE_FILE_OFFSET64

From: Cyril Hrubis <chrubis@suse.cz>
To: Florian Weimer <fweimer@redhat.com>
Cc: Jeff Layton <jlayton@redhat.com>,
	Mike Frysinger <vapier@gentoo.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
	libc-alpha@sourceware.org, linux-fsdevel@vger.kernel.org,
	Carlos O'Donell <carlos@redhat.com>,
	Yuriy Kolerov <Yuriy.Kolerov@synopsys.com>
Subject: Re: [glibc PATCH] fcntl: put F_OFD_* constants under #ifdef __USE_FILE_OFFSET64
Date: Tue, 23 Aug 2016 13:03:43 +0200	[thread overview]
Message-ID: <20160823110343.GA4962@rei.suse.cz> (raw)
In-Reply-To: <8e1a972a-7966-139b-9d75-6d3a847a1be8@redhat.com>

Hi!
> > So yeah, I think what I proposed before would probably be fine. But now
> > that Michael pushed the issue, it's dawned on me that we may be able to
> > get away with supporting it better if we turn the compatability
> > mechanism on its head and use F_OFD_*32 constants in the non-LFS case.
> 
> That's rather confusing to programmers, though.
> 
> We then have:
> 
> F_OFD_SETLK     always 64-bit
> F_SETLK         32-bit or 64-bit
> F_SETLK64       always 64-bit (not recommended)
> F_OFD_SETLK32   always 32-bit

It's even worse, the F_OFD_SETLK32 in the proposed patch behaves exactly
as F_SETLK so it's 32-bit or 64-bit depending on sizeof(long) in the
kernel, that is because the compat fcntl64 converts struct flock from
userspace to kernel struct flock and just call sys_fcntl() with the cmd
it has. So in the end if you call fcntl with F_OFD_SETLK32 on 64bit
kernel it expects flock64.

-- 
Cyril Hrubis
chrubis@suse.cz