Date: Fri, 15 Aug 2014 20:30:48 +0200 From: Oliver Pinter <oliver.pntr@gmail.com> To: Warner Losh <imp@bsdimp.com> Cc: Marcel Moolenaar <marcel@freebsd.org>, Phil Shafer <phil@juniper.net>, John-Mark Gurney <jmg@funkthat.com>, "Simon J. Gerraty" <sjg@juniper.net>, arch@freebsd.org, Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-arch <freebsd-arch@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com> Subject: Re: XML Output: libxo - provide single API to output TXT, XML, JSON and HTML Message-ID: <CAPjTQNH0vTo2yA0etesPV7os7YmowqTEevqFfpR_hM_HuCYxqA@mail.gmail.com> In-Reply-To: <94A47A7D-89C9-4504-B669-2A5EDA80373B@bsdimp.com> References: <20140814052648.GM2737@kib.kiev.ua> <201408140606.s7E66XXA091972@idle.juniper.net> <20140814085257.GN2737@kib.kiev.ua> <201408140847.00573.jhb@freebsd.org> <94A47A7D-89C9-4504-B669-2A5EDA80373B@bsdimp.com>
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On 8/14/14, Warner Losh <imp@bsdimp.com> wrote: > > On Aug 14, 2014, at 6:47 AM, John Baldwin <jhb@freebsd.org> wrote: > >>>> Marking the binary with a libxo-specific note tells the caller that >>>> the binary is capable of rendering its output in a non-traditional >>>> style and gives the caller a means of triggering those styles of >>>> output. In the libxo-enabled world, I see this as vital information >>>> the caller needs to initialize the environment in which the command >>>> will be run. Isn't this exactly the sort of information ELF targets >>>> for note sections? >>> >>> How binary format has any relevance for an application level feature ? >>> What would you do with the binaries which permissions are 'r-s--x--x', >>> which is not unexpected for the tools which gather system information >>> and have to access things like /dev/mem ? >>> >>> You removed and did not answered a crusial question, which is a litmus >>> test for your proposal. Namely, how presence of the proposed note in >>> the binary is different from DT_NEEDED tag for your library ? >> >> Yes, checking DT_NEEDED for libxo.so is the first thing I thought of as >> well. >> It is equivalent to 'ldd foo | grep libxo'. > > Doesn't work for static binaries, nor for cases where libxo is linked in by > a > library indirectly, nor for when the command is a shell script that may > invoke a command that supports this output, nor for a python script that > implements this output, etc. > > My question for people advocating this method: Why not require all commands > that generate this kind of output to support a standard command line option > that causes the command to print nothing and return 0 if it supports > reporting, > or anything else if it doesn't (return 0 with output, or return non-zero > with or without > output). This would handle the more complicated implementation issues with > using > DT_NEEDED and/or the ELF note, be more in line with how things are > traditionally > done, and offer greater flexibility of implementation. > > Warner What's about extending standard file descriptors? Example by: 0: stdin 1: stdout 2: stderr N: extended stdin N+1: extended stdout N+2: extended stderr If the program can not open fd [0-2], then in fallback case can try to open fd [N-N+2]. >
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