XML Output: libxo - provide single API to output TXT, XML, JSON and HTML

[Warner Losh]

On Aug 14, 2014, at 6:47 AM, John Baldwin <jhb at 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
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