Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751901AbdHGUVB (ORCPT ); Mon, 7 Aug 2017 16:21:01 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:35646 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751429AbdHGUU7 (ORCPT ); Mon, 7 Aug 2017 16:20:59 -0400 MIME-Version: 1.0 In-Reply-To: <20170807164505.GC4474@magnolia> References: <20170806164428.2273-1-mikko.rapeli@iki.fi> <20170806164428.2273-34-mikko.rapeli@iki.fi> <20170807155445.GA4074@magnolia> <20170807164505.GC4474@magnolia> From: Arnd Bergmann Date: Mon, 7 Aug 2017 22:20:58 +0200 X-Google-Sender-Auth: Z4HntpugMqbnxuypoiNFX3McPvo Message-ID: Subject: Re: [PATCH v06 33/36] uapi linux/fsmap.h: use __kernel_size_t instead of size_t To: "Darrick J. Wong" Cc: Mikko Rapeli , Linux Kernel Mailing List , Linux API , "Theodore Ts'o" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1647 Lines: 36 On Mon, Aug 7, 2017 at 6:45 PM, Darrick J. Wong wrote: > On Mon, Aug 07, 2017 at 06:01:43PM +0200, Arnd Bergmann wrote: >> On Mon, Aug 7, 2017 at 5:54 PM, Darrick J. Wong wrote: >> > On Sun, Aug 06, 2017 at 06:44:24PM +0200, Mikko Rapeli wrote: >> >> Either way works, but including a system header from a kernel header >> requires an additional "#ifndef __KERNEL__" check, so I think Miko's >> variant is a little nicer. >> >> Generally speaking, you also want to avoid including system headers >> indirectly from kernel headers, as POSIX requires that including one >> system header should not indirectly make symbols from other system >> headers visible. I think this is not a problem here though, as no system >> header should include linux/fsmap.h. > > Sorry, I guess I was a little unclear about what I was asking -- I was > wondering why can't the userspace program include sys/types.h prior to > linux/fsmap.h? I wasn't proposing including C library headers in kernel > headers. > > I think the patch author is pushing towards kernel headers never relying > on /anything/ in the system headers. Right, and I think that is a good thing to have, because it allows us to do better compile-time testing of the exported kernel headers. > For data structures being > exchanged with the kernel I agree, but the fsmap_sizeof result is never > passed to or received from the kernel; it exists purely for malloc > convenience. Would you prefer making fsmap_sizeof a macro? That would also make it possible to do static checking on the header without having to resort to odd types. Arnd