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[[!meta title="Fixing Programs Using PATH_MAX et al Unconditionally"]]

POSIX describes some constants (or rather macros) like PATH_MAX/MAXPATHLEN and
similar, which may be defined by the system to indicate certain limits. Many
people overlook the *may* though: Systems only should define them if they
actually have such fixed limits (see [limits.h](http://pubs.opengroup.org/onlinepubs/009695399/basedefs/limits.h.html)). The Hurd, following the GNU Coding Standards,
tries to avoid this kind of arbitrary limits, and consequently doesn't define
the macros.

Many programs however just assume their presence, and use them unconditionally.
This is simply sloppy coding: not only does it violate POSIX and fails on
systems not defining the macros, but in fact most common use cases of these
macros are simply wrong! (See
<http://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html> for some
hints as to why this is so.)

There are a few hundred packages in Debian GNU/Hurd failing to build because of
this -- simply grep for the offending macros in the
[list_of_build_failures](http://unstable.buildd.net/buildd/hurd-i386_Failed.html).

Fixing these issues usually boils down to replacing `char foo[PATH_MAX]`
by `char *foo`, and using dynamic memory allocation, i.e. e.g. a loop
that tries geometrically growing sizes. Sometimes this is tricky, but
more often not very hard. Sometimes it is even trivial because the GNU
system has proper replacements. See the corresponding section of the
[[porting_guidelines_page|hurd/porting/guidelines]] for more details. With a bit of
practice, it should be easily possible to fix several programs per day.

The goal of this project is to fix the PATH_MAX and related problems in a
significant number of packages, and make the fixes ready for inclusion in
Debian and (where possible) upstream. No Hurd-specific knowledge is needed, nor
any other special knowledge aside from general C programming skills.

Possible mentors: Samuel Thibault (youpi)

Exercise: Fix the PATH_MAX issues in some Debian package.