Date: Sat, 17 Dec 2016 00:52:21 -0800 From: Adrian Chadd <adrian.chadd@gmail.com> To: Eric van Gyzen <vangyzen@freebsd.org> Cc: Warner Losh <imp@bsdimp.com>, John Baldwin <jhb@freebsd.org>, Dimitry Andric <dim@freebsd.org>, Baptiste Daroussin <bapt@freebsd.org>, "Conrad E. Meyer" <cem@freebsd.org>, src-committers <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r310138 - head/lib/libc/stdio Message-ID: <CAJ-Vmo=zpBwnEEmjLyactRSrQWNpVq1-bFn%2B-e3Z3qTxS5cskw@mail.gmail.com> In-Reply-To: <e2056221-26ad-5108-3385-865abff12d78@FreeBSD.org> References: <201612160144.uBG1ipjW016736@repo.freebsd.org> <13059937.h5mayX8aKo@ralph.baldwin.cx> <9e255301-f663-a96c-68c7-e6d1a3d1db8c@FreeBSD.org> <3160837.brVkGGj5yS@ralph.baldwin.cx> <CANCZdfrNu0=qPuMX8SA2H-MUXGb5rei06_dQg9XGp-Miu3Xsfg@mail.gmail.com> <e2056221-26ad-5108-3385-865abff12d78@FreeBSD.org>
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... just have printf_freebsd in libutil; have it know about our extended fmt types. then we just have to port libutil to a target platform. -a On 16 December 2016 at 17:31, Eric van Gyzen <vangyzen@freebsd.org> wrote: > On 12/16/2016 17:44, Warner Losh wrote: >> On Fri, Dec 16, 2016 at 3:07 PM, John Baldwin <jhb@freebsd.org> wrote: >>> On Friday, December 16, 2016 04:53:04 PM Eric van Gyzen wrote: >>>> 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. >>> >>> Hmm, that might work, but it is still cumbersome. Probably to make things readable >>> we'd end up with a wrapper: >>> >>> printb(uint val, const char *fmt) >>> { >>> char buf[strlen(fmt) + C]; >>> >>> snprintb(...); >>> printf("%s", buf); >>> } >> >> Sadly this "cure" is worse than the disease. > > How about this cure? > > printf("reg=%b\n", value, FORMAT); > > // versus > > char buf[BITMASK_BUFFER_SIZE(FORMAT)]; > printf("reg=%s\n", format_bitmask(buf, sizeof(buf), value, FORMAT)); > > That doesn't seem so bad. > > Eric >
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