Re: Unused sys/ucontext.h files

[Roland McGrath <roland@hack.frob.com>]

Yes, the sysdeps/arm file will (probably) be used by the arm-nacl
configuration.

In general, I am against removing files of this category just because
they are not used by any current configuration.  That is, files that are
machine-specific and for a machine that has some configurations in
current use, but are OS-independent.  I put them in the same category as
the stub files, most of which are not used by any configuration that can
be built.  Stubs of function implementations provide the outline of the
API and a starting point for filling in actual implementations.
Similarly, pure machine-specific files provide at least the basics of
the machine-specific API that should make sense across all OS
configurations of libc for that machine.

As with the stub implementations, there is of course always the danger
of bit rot.  As much as possible, all of libc's APIs are meant to be
independent of the underlying operating system.  That being the case,
people making API changes should endeavor to notice all the different
implementations and update them consistently.  People will forget, some
changes will be untested, etc.  But we should still be striving to
consider OS independence issues in all of our API choices.  Any time
there is an API whose only implementations that exist in our sources are
for a particular operating system, there is a much increased risk that
future changes will introduce or further enshrine assumptions about the
underlying operating system that make it more difficult (or impossible)
to implement that API elsewhere later on.


Thanks,
Roland