svn commit: r310138 - head/lib/libc/stdio

[John Baldwin]

On Friday, December 16, 2016 08:53:26 PM Dimitry Andric wrote:
> On 16 Dec 2016, at 20:31, Baptiste Daroussin <bapt at FreeBSD.org> wrote:
> > 
> > On Fri, Dec 16, 2016 at 01:44:51AM +0000, Conrad E. Meyer wrote:
> >> Author: cem
> >> Date: Fri Dec 16 01:44:50 2016
> >> New Revision: 310138
> >> URL: https://svnweb.freebsd.org/changeset/base/310138
> >> 
> >> Log:
> >>  vfprintf(3): Add support for kernel %b format
> >> 
> >>  This is a direct port of the kernel %b format.
> >> 
> >>  I'm unclear on if (more) non-portable printf extensions will be a
> >>  problem. I think it's desirable to have userspace formats include all
> >>  kernel formats, but there may be competing goals I'm not aware of.
> >> 
> >>  Reviewed by:	no one, unfortunately
> >>  Sponsored by:	Dell EMC Isilon
> >>  Differential Revision:	https://reviews.freebsd.org/D8426
> >> 
> > 
> > I really don't think it is a good idea, if used in userland it would be make
> > more of our code difficult to port elsewhere.
> 
> Indeed, this is a bad idea.  These custom format specifiers should be
> eliminated, not multiplied. :-)
> 
> 
> > Other than that, it makes more difficult to use vanilla gcc with out userland.
> > and it is adding more complexity to be able to build freebsd from a non freebsd
> > system which some people are working on.
> > 
> > Personnaly I would prefer to see those extensions removed from the kernel rather
> > than see them available in userland.
> 
> Same here.
> 
> 
> > Can't we use simple helper function instead?
> 
> Yes, please.  Just take the snprintb(3) function from NetBSD:
> 
> http://netbsd.gw.com/cgi-bin/man-cgi?snprintb+3+NetBSD-current

In general I agree with something like this instead, but it is quite a bit more
tedious to use as you have to run it once to determine the length, allocate a
buffer, and then run it again.  Calling malloc() for that buffer isn't always
convenient in the kernel (though it should be fine in userland).  Having it live
in printf() itself means the output is generated to the stream without having to
manage a variable-sized intermediate buffer.

-- 
John Baldwin