From f4b3ff3c40fac32f395b83a6c753ff8f7d2ded8b Mon Sep 17 00:00:00 2001
From: Steve Baker <sbaker@redhat.com>
Date: Fri, 22 Apr 2022 14:29:53 +1200
Subject: [PATCH] Add chroot support to tripleo-mount-image

This change adds support for immediately starting a chroot when an
image has been mounted.

This is convenient since many uses of tripleo-mount-image will require
running commands inside the image (such as dnf install). Starting a
useful chroot is slightly involved since it requires bind-mounting
/dev and copying in /etc/resolve.conf. This change handles that, as
well as cleanup and automatic unmount on exit.

This change also makes the -m <directory> command optional, when not
specified a temp directory will be created and used as the mount
directory.

Change-Id: I533ce13833bbfaab0ede3a11b6c22e45fe767939
---
 scripts/tripleo-mount-image | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/scripts/tripleo-mount-image b/scripts/tripleo-mount-image
index 1128b441d..c4266d410 100755
--- a/scripts/tripleo-mount-image
+++ b/scripts/tripleo-mount-image
@@ -24,6 +24,7 @@ SCRIPT_NAME=$(basename $0)
 NBD_DEVICE=""
 IMAGE_FILE=""
 MOUNT_DIR=""
+CHROOT=""
 if [ ! -a "/dev/nbd0" ]; then
     modprobe nbd
 fi
@@ -55,6 +56,8 @@ mount_show_options() {
     echo "    -m <directory>              -- Directory to mount image to."
     echo "    -n <nbd device>             -- NBD device to use (example, /dev/nbd0)."
     echo "                                   Defaults to first available"
+    echo "    --chroot                    -- Start a working chroot which is active until exit."
+    echo "                                   Directory will be unmounted on chroot exit"
     echo
     echo "Mount an overcloud image to a directory"
     echo
@@ -96,6 +99,28 @@ remove_device () {
     fi
 }
 
+start_chroot () {
+    EACTION="echo Exited chroot, unmounting $MOUNT_DIR ; unmount_image"
+    trap "$EACTION" EXIT
+
+    mount -o bind /dev $MOUNT_DIR/dev/
+    EACTION="umount $MOUNT_DIR/dev/; $EACTION"
+    trap "$EACTION" EXIT
+
+    if [ -a $MOUNT_DIR/etc/resolv.conf ]; then
+        mv $MOUNT_DIR/etc/resolv.conf $MOUNT_DIR/etc/resolv.conf.tmi
+        EACTION="mv $MOUNT_DIR/etc/resolv.conf.tmi $MOUNT_DIR/etc/resolv.conf; $EACTION"
+        trap "$EACTION" EXIT
+    fi
+
+    cp /etc/resolv.conf $MOUNT_DIR/etc/resolv.conf
+    EACTION="rm $MOUNT_DIR/etc/resolv.conf; $EACTION"
+    trap "$EACTION" EXIT
+
+    echo "Starting chroot in $MOUNT_DIR, exit will also unmount"
+    PS1="[\u@chroot \W]\$ " chroot $MOUNT_DIR /bin/bash -l
+}
+
 mount_image() {
     set -x
 
@@ -266,7 +291,7 @@ if [ $SCRIPT_NAME == "tripleo-unmount-image" ]; then
     fi
     unmount_image
 else
-    TEMP=`getopt -o ha:m:n: -l help -n $SCRIPT_NAME -- "$@"`
+    TEMP=`getopt -o ha:m:n: -l help,chroot -n $SCRIPT_NAME -- "$@"`
     if [ $? != 0 ]; then
         echo "Terminating..." >&2
         exit 1
@@ -280,11 +305,15 @@ else
             -a) IMAGE_FILE=$2 ; shift 2;;
             -m) MOUNT_DIR=$2 ; shift 2;;
             -n) NBD_DEVICE=$2 ; shift 2;;
+            --chroot) CHROOT=yes ; shift;;
             --) shift ; break;;
             *) echo "Error: unsupported option $1." ; exit 1;;
         esac
     done
-    if [ -z "${MOUNT_DIR}" ] || [ -z "${IMAGE_FILE}" ]; then
+    if [ -z "${MOUNT_DIR}" ]; then
+        MOUNT_DIR=$(mktemp -d)
+    fi
+    if [ -z "${IMAGE_FILE}" ]; then
         mount_show_options 1
     fi
     MOUNT_DIR=$(realpath ${MOUNT_DIR})
@@ -307,4 +336,7 @@ else
         fi
     fi
     mount_image
+    if [ -n $CHROOT ]; then
+        start_chroot
+    fi
 fi
\ No newline at end of file