linkat returns EISDIR when target exists

[Simon Josefsson]

Hi!

I'm porting some software to Debian GNU/Hurd and I think the issues I
found are bugs in the Hurd.  I haven't reported bugs about the Hurd
before, and I'm unsure whether this is an issue with the kernel or libc
or some translator, but I'm hoping someone here will know what code to
patch.

As diagnosed under 1) here:

https://lists.gnu.org/archive/html/bug-gnulib/2011-08/msg00027.html

it seems that the linkat function returns EISDIR when the target file
exists.

I don't see EISDIR as a documented return code of linkat in POSIX:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/link.html

instead I see the seemingly appropriate EEXIST documented like this:

[EEXIST]
    The path2 argument resolves to an existing directory entry or refers
    to a symbolic link.

Maybe just a s/EISDIR/EEXIST/ at the appropriate place?

/Simon