selftest: Add helper scripts for accessing the testenv namespace

This patch adds some helper scripts that make talking to a given
testenv's namespace slightly easier.

One of the really cool things about namespaces is you can run multiple
different programs that can all talk to the testenv DC. However, the
command to do this is a bit unweildly, it's based on PID so it changes
everytime you start up a testenv, and you loose all the environment
variables that selftest normally sets up.

This patch adds a couple of helper scripts:
- nsenter-helper.sh: this takes the variables defined in an exports_file
  and exports them all. It prints some basic help and then starts a new
  shell session (this whole script gets run in the new namespace).
  Essentially this achieves something similar to the legacy
  selftest-vars.sh script (except this one actually works).
- mk_nsenter.sh: this generates a simple wrapper script that'll run
  nsenter and then call nsenter-helper.sh. A separate wrapper script
  gets created for each testenv. E.g. to run it, just go:
    ./st/ad_dc/nsenter.sh

  This is a wrapper for a more complicated command underneath like:
    nsenter -t 437353 --net --user --preserve-credentials \
      /home/timbeale/code/samba/selftest/ns/nsenter-helper.sh \
      /home/timbeale/code/samba/st/ad_dc/exports.sh

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

selftest/ns/mk_nsenter.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+#
+# Helper script. If you want a 2nd shell that communicates with the testenv DC
+# you can use the nsenter command to change the namespace you're in. However,
+# this command is a bit unwieldly and changes depending on the testenv PID.
+# We can generate a helper script on the fly that abstracts all this
+# complexity, allowing you to use the same, simple command to change the
+# namespace that you're in, e.g.
+#   st/ad_dc/nsenter.sh
+
+pid=$1
+exports_file=$2
+
+# The basic command to enter the testenv's network namespace.
+# We enter the user namespace as well (as ourself, which is really the root
+# user for the namespace), otherwise we need sudo to make this work.
+nsenter_cmd="nsenter -t $pid --net --user --preserve-credentials"
+
+# By default, the nsenter command will just start a new shell in the namespace.
+# we use a wrapper helper script, which first loads all the environment
+# variables that are usually defined in selftest (and prints some basic help).
+helper_script="$(dirname $0)/nsenter-helper.sh $exports_file"
+
+# generate the dynamic script
+dyn_script="$(dirname $2)/nsenter.sh"
+echo "#!/bin/sh" > $dyn_script
+echo "$nsenter_cmd $helper_script" >> $dyn_script
+chmod 755 $dyn_script
+
+# return the script we created
+echo "$dyn_script"
+

selftest/ns/nsenter-helper.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+# Helper script that gets run with nsenter to manually setup a secondary shell
+# session to a given namespace testenv. This basically just sets up the same
+# environment variables as you normally get with selftest, for convenience.
+
+if [ $# -lt 1 ] ; then
+    echo "Usage: $0 <exports-file>"
+    exit 1
+fi
+
+# we get passed a exports file with all the environment variables defined
+exports_file=$1
+
+# read the exports file so the new shell has appropriate variables setup
+# (we export rather than sourcing here so they get inherited by the subshell)
+while read -r line ; do
+    export $line
+    # dump them for the user too
+    echo $line
+done < $exports_file
+
+echo ""
+echo "Entered $NETBIOSNAME namespace, with above variables defined."
+echo "Use CTRL+D or exit to leave the namespace."
+echo ""
+
+# start a shell session in the new namespace
+$SHELL
+
+

selftest/ns/start_in_ns.sh

@@ -17,9 +17,14 @@ parent_pid=$3
 # The namespaces we use are anonymous, which means other processes would need
 # to use our PID to access the new namespace
 echo "-------------------------------------------------------------"
-echo "Created namespace for $NETBIOSNAME"
-echo "To communicate with this testenv, use: nsenter -t $$ --net sh"
-echo "To copy its environment variables, use: . $exports_file"
+echo "Created namespace for $NETBIOSNAME ($ENVNAME) PID $$"
+
+# generate a helper script if the developer wants to talk to this namespace
+# in another shell
+mk_nsenter_script="$(dirname $0)/mk_nsenter.sh"
+helper_script=$($mk_nsenter_script $$ $exports_file)
+
+echo "To communicate with this testenv, use: $helper_script"
 echo "-------------------------------------------------------------"
 
 # the rest of the args are the samba command to run