chroot: don't chdir() if not changing root

This allows chroot to be used as a light weight tool
to change user identification for a command,
while not changing the current working directory.
It also makes `chroot / true` consistently succeed on
all platforms for non root users.

* src/chroot.c (main): If the same root is specified. i.e. '/'
then don't change the current working directory, and avoid the
overhead of the other redundant calls.
* tests/misc/chroot-fail.sh: Remove failure guard previously
needed on some systems.  Also add an explicit case to ensure
we don't change directory.
* NEWS: Mention the change in behavior.

1 files changed, 3 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index c204b680d..93e3a0980 100644
--- a/NEWS
+++ b/NEWS
@@ -82,6 +82,9 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 ** Changes in behavior
 
+  chroot with an argument of "/" no longer implicitly changes the current
+  directory to "/", allowing changing only user credentials for a command.
+
   ls with none of LS_COLORS or COLORTERM environment variables set,
   will now honor an empty or unknown TERM environment variable,
   and not output colors even with --colors=always.