linux-kernel - Re: [PATCH v06 33/36] uapi linux/fsmap.h: use __kernel_size_t instead of size

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Date:   Tue, 8 Aug 2017 16:08:26 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Mikko Rapeli <mikko.rapeli@....fi>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH v06 33/36] uapi linux/fsmap.h: use __kernel_size_t
 instead of size_t

On Mon, Aug 07, 2017 at 10:20:58PM +0200, Arnd Bergmann wrote:
> On Mon, Aug 7, 2017 at 6:45 PM, Darrick J. Wong <darrick.wong@...cle.com> 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 <darrick.wong@...cle.com> 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.

Ick, no macros, please. :)

How about just change it to unsigned long long and call it a day?

--D

> 
>       Arnd
> --
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