Re: Compatability: aufs-utils needs GNU extensions to nftw

[Rich Felker <dalias@aerifal.cx>]

On Tue, Jan 01, 2013 at 02:33:36PM -0800, idunham@lavabit.com wrote:
> One of the Puppy developers recently mentioned that he'd like to build
> mount.aufs with musl because the static binary is excessively large (600
> kb) when built with glibc.
> However, there are a couple issues:
> 1. The most important issue is that libau uses the following flags/macros:
> FTW_ACTIONRETVAL
> FTW_CONTINUE
> FTW_SKIP_SUBTREE
> FTW_SKIP

Are you sure it really _needs_ them? They seem to be mostly
optimizations to avoid walking uninteresing parts of the tree, and it
should be possible to achieve the same behavior (aside from time
wasted walking uninteresting stuff) with minor changes to the callback
function...

> >From all I can see, this would require some extensions to nftw() and
> possibly  to fn().
> I'm not sure exactly what glibc does with these, so I have no idea what to
> do.

This doesn't seem so bad, and probably could be added. But I'd like to
overhaul ftw anyway to use the *at functions instead of concatenating
paths, and to avoid recursion, and to handle the fd limit right. At
present I would say we have a very poor implementation. On the bright
side, these functions are so bad that correct software should not be
using them; they don't pass any context back to the callback, so the
only way to use them is with global or thread-local vars...

Rich