Date: Fri, 16 Dec 2016 16:53:04 -0600 From: Eric van Gyzen <vangyzen@FreeBSD.org> To: John Baldwin <jhb@freebsd.org>, Dimitry Andric <dim@freebsd.org> Cc: Baptiste Daroussin <bapt@freebsd.org>, "Conrad E. Meyer" <cem@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r310138 - head/lib/libc/stdio Message-ID: <9e255301-f663-a96c-68c7-e6d1a3d1db8c@FreeBSD.org> In-Reply-To: <13059937.h5mayX8aKo@ralph.baldwin.cx> References: <201612160144.uBG1ipjW016736@repo.freebsd.org> <20161216193128.wgskqt4vc44vdd7o@ivaldir.etoilebsd.net> <8CF1AB9C-83FE-495F-B07C-56F928282512@FreeBSD.org> <13059937.h5mayX8aKo@ralph.baldwin.cx>
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On 12/16/2016 16:45, John Baldwin wrote: > On Friday, December 16, 2016 08:53:26 PM Dimitry Andric wrote: >> On 16 Dec 2016, at 20:31, Baptiste Daroussin <bapt@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. I imagine most callers can simply use a char[sizeof(fmt)+C] on the stack, where C is some constant that I haven't taken the time to calculate, at the risk of making myself look foolish and unprofessional. Eric
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