Precheck to avoid overwriting installed systems during prestaging

When booting the system with the prestaging ISO, check for the
presence of a valid installation.

Avoid overwriting an existing installation with a message to the
user.

Test Plan:

PASS: Verify that an existing installation is not overwritten by
      the prestaging operation

PASS: Verify failure handling of the prestaging operation with
      a message to the user, when an installation already exists
      on the subcloud.

PASS: Verify successful prestaging operation when there is no
      existing installation on the subcloud.

Story: 2009948
Task: 44872

Change-Id: I47e4f67f001da208f4e823ac699473c89b638ce5
Signed-off-by: Shrikumar Sharma <shrikumar.sharma@windriver.com>

bsp-files/centos-ks-gen.pl

@@ -87,6 +87,7 @@ write_config_file("controller-worker-lowlatency",
 #
 write_config_file("controller",
                   "${output_dir}/prestaged_installer_ks.cfg",
+                  "pre_prestaging_install_check.cfg",
                   "pre_common_head.cfg",
                   "pre_pkglist_prestage.cfg",
                   "pre_disk_setup_common.cfg",

bsp-files/kickstarts/pre_prestaging_install_check.cfg

@@ -0,0 +1,66 @@
+%pre --erroronfail
+
+# Get the FD used by subshells to log output
+exec {stdout}>&1
+
+# Source common functions
+. /tmp/ks-functions.sh
+
+wlog "pre prestaging install check"
+
+# First, parse /proc/cmdline to find the boot args
+set -- `cat /proc/cmdline`
+for I in $*; do case "$I" in *=*) eval $I 2>/dev/null;; esac; done
+
+if [ -z "$rootfs_device" ]; then
+    rootfs_device=$(get_disk_dev)
+fi
+
+orig_rootfs_device=$rootfs_device
+by_path_rootfs_device=$(get_by_path $rootfs_device)
+rootfs_device=$(get_disk $by_path_rootfs_device)
+wlog "Found rootfs $orig_rootfs_device on: $by_path_rootfs_device->$rootfs_device."
+
+part_numbers=( $(parted -s ${rootfs_device} print | awk '$1 == "Number" {i=1; next}; i {print $1}') )
+# print the partnumber info for informational purposes
+for i in ${part_numbers[@]}; do
+    wlog "partnumber: ${i}"
+done
+
+# Get the correct rootfs prefix
+ROOTFS_PART_PREFIX=${rootfs_device}
+# check if rootfs part is nvme (eg. /dev/nvme0n1). The partitions have a "p" in the part prefix.
+# for example, /dev/nvme0n1p1
+# so we need to add the letter "p" to get the prefix.
+# The part numbers will be used later in the code.
+case $rootfs_device in
+    *"nvme"*)
+        ROOTFS_PART_PREFIX=${ROOTFS_PART_PREFIX}p
+    ;;
+esac
+
+# temporary mount directory
+temp_mount=/mnt
+
+wlog "Searching for existing installation..."
+for part in "${part_numbers[@]}"; do
+    device=${ROOTFS_PART_PREFIX}${part}
+    wlog "Searching on ${device}"
+    # mount this part at a temporary mount point
+    mount ${device} ${temp_mount}
+    if [ $? -ne 0 ]; then
+        wlog "unable to mount ${device}"
+        continue
+    fi
+    # Check for the presence of install_uuid in one of the partitions on
+    # the root device
+    if [ -e ${temp_mount}/var/www/pages/feed/rel-xxxPLATFORM_RELEASExxx/install_uuid ]; then
+        wlog "Found valid installation on ${device}"
+        umount ${temp_mount}
+        # do not modify the system in any way
+        report_pre_failure_with_msg "Prestage rejected. Existing installation detected. Please eject the media before rebooting."
+    fi
+    wlog "Unmounting ${device}"
+    umount ${temp_mount}
+done
+%end