bug#8850: mkdir inside symlink creates wrong directory with relative parent

[Oldřich Jedlička]

Hi all,

I was trying to search for any description helping me understand in
what I see, but actually I didn't find any, so I'm here. I discovered
it by using automake-1.11, because it uses relative paths a lot. So my
simplified testcase is as follows:

Have a directory structure x/y and x/z/a. Have a symbolic link from
x/y/z that points to x/z.

 mkdir -p x/y
 mkdir -p x/z/a
 ln -s ../z x/y/z

Now go into x/y/z/a and try to create directory like that:

 cd x/y/z/a
 mkdir ../dir_xyz
 mkdir ../../dir_xy
 mkdir ../../../dir_x

I would expet that there would be a directory like this:

 x/dir_x
 x/y/dir_xy
 x/y/z/dir_xyz (x/z/dir_xyz)

But the result is completely different:

 dir_x
 x/dir_xy
 x/y/z/dir_xyz (x/z/dir_xyz)

So when you want to create a directory in the parent structure from
within the symbolic link, you will fail in doing so, because the
symbolic link would be resolved during walking through parents, so you
can get to completely different tree while creating your directory. It
looks like a bug, because it is nowhere documented to behave like that
(and the behaviour is strange by itself).

Verified on Debian 4.0/RedHat 5.4 with coreutils 5.97 and on Gentoo
with coreutils 8.12.

Regards,
Oldrich.