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✏️ Editing: 490_fix_broken_links.sh

# build/default/490_fix_broken_links.sh
#
# Check for broken symbolic links inside the recovery system in ROOTFS_DIR
# and add missing symlink targets to the recovery system
# when the symlink target is a file (and not a directory)
# see https://github.com/rear/rear/issues/1638
# and https://github.com/rear/rear/pull/1734

# Some broken symlinks are expected. The 'build' and 'source' symlinks in kernel modules point to kernel sources
# and are broken untol one installs the kernel-debug-devel or kernel-devel packages (on Fedora) and even then
# the targets are jot included in the rescue system by default.
# Do not warn about those, it is just noise.
local irrelevant_symlinks=( '*/lib/modules/*/build' '*/lib/modules/*/source' )
function symlink_is_irrelevant () {
    for i in "${irrelevant_symlinks[@]}"; do
        # do not quote $i, it is a glob pattern, matching will be performed by [[ ... == ... ]]
        # quoting inside [[ ]] prevents pattern matching
        if [[ "$1" == $i ]]; then
            return 0
        fi
    done
    return 1
}

# FIXME: The following code fails if symlinks or their targets contain characters from IFS (e.g. blanks),
# cf. the same kind of comments in build/default/990_verify_rootfs.sh
# and layout/prepare/GNU/Linux/130_include_mount_subvolumes_code.sh
# see https://github.com/rear/rear/pull/1514#discussion_r141031975
# and for the general issue see https://github.com/rear/rear/issues/1372

# Find broken symbolic links inside the recovery system via 'chroot $ROOTFS_DIR find / -xtype l'
# (but exclude the special proc sys dev directories inside the recovery system)
# because 'pushd $ROOTFS_DIR ; find . -xtype l ; popd' would not find symlinks that are broken
# within the recovery system because the symlink target is outside of the recovery system,
# for example $ROOTFS_DIR/etc/localtime -> /usr/share/zoneinfo/Europe/Berlin is broken
# and should be $ROOTFS_DIR/etc/localtime -> $ROOTFS_DIR/usr/share/zoneinfo/Europe/Berlin
# cf. https://github.com/rear/rear/pull/1734#issuecomment-434635175
# Eveny broken symlink has the form of an absolute path inside ROOTFS_DIR, for example:
#   /etc/localtime                       (e.g. with link target /usr/share/zoneinfo/Europe/Berlin)
#   /etc/mtab                            (e.g. with link target /proc/1234/mounts)
#   /etc/termcap                         (e.g. with link target /usr/share/misc/termcap)
#   /dir1/dir2/relative_symlink_to_file  (e.g. with link target ../../path/to/file)
#   /dir3/relative_symlink_to_directory  (e.g. with link target ../path/to/directory)
local broken_symlinks=$( chroot $ROOTFS_DIR find / -xdev -path '/proc' -prune -o -path '/sys' -prune -o -path '/dev' -prune -o -xtype l -print )

# Copy missing symlink targets into the recovery system if the symlink target exists
# (except the symlink target is in /proc/ /sys/ /dev/ or /run/).
# Otherwise report that there is something wrong on the original system and
# assume when things work sufficiently on the original system nevertheless
# this is no sufficient reason to abort here (i.e. proceed "bona fide")
# cf. what is done when '$lib is a symbolic link' in build/GNU/Linux/390_copy_binaries_libraries.sh
pushd $ROOTFS_DIR
    local broken_symlink=''
    local link_target=''
    for broken_symlink in $broken_symlinks ; do
        if symlink_is_irrelevant "$broken_symlink" ; then
            DebugPrint "Ignoring irrelevant broken symlink $broken_symlink"
            continue
        fi
        # For each broken symlink absolute path inside ROOTFS_DIR
        # we call "readlink -e" in the original system to get its link target there.
        # If in the original system there was a chain of symbolic links like
        #   /some/path/to/file1 -> /another/path/to/file2 -> /final/path/to/file3
        # where $broken_symlink='/some/path/to/file1' and $link_target='/final/path/to/file3'
        # the chain of symbolic links gets simplified in the recovery system to $broken_symlink -> $link_target like
        #   /some/path/to/file1 -> /final/path/to/file3
        link_target=$( readlink $v -e $broken_symlink )
        # The '-e' option results that every link_target has the form of an absolute path,
        # in particular also link targets of relative symlinks,
        # for example for the above broken symlink examples each link_target could be like:
        #   /usr/share/zoneinfo/Europe/Berlin  (e.g. the link target of /etc/localtime)
        #   /proc/1234/mounts                  (e.g. the link target of /etc/mtab)
        #   /usr/share/misc/termcap            (e.g. the link target of /etc/termcap)
        #   /path/to/file                      (e.g. the link target of /dir1/dir2/relative_symlink_to_file)
        #   /path/to/directory                 (e.g. the link target of /dir3/relative_symlink_to_directory)
        if [[ -d "$link_target" ]]; then
            LogPrintError "Symlink '$broken_symlink' -> '$link_target' refers to a non-existing directory on the recovery system."
            LogPrintError "It will not be copied by default. You can include '$link_target' via the 'COPY_AS_IS' configuration variable."
        elif test "$link_target" ; then
            # Never copy symlink targets in /proc/ /sys/ /dev/ or /run/ into the ReaR recovery system
            # for example the symlink /etc/mtab that points to /proc/self/mounts
            # cf. https://github.com/rear/rear/issues/2111
            # also cf. the scripts
            # finalize/GNU/Linux/250_migrate_disk_devices_layout.sh
            # finalize/GNU/Linux/250_migrate_lun_wwid.sh
            # finalize/GNU/Linux/280_migrate_uuid_tags.sh
            # finalize/GNU/Linux/320_migrate_network_configuration_files.sh
            if echo $link_target | egrep -q '^/(proc|sys|dev|run)/' ; then
                DebugPrint "Skip copying broken symlink '$broken_symlink' target '$link_target' on /proc/ /sys/ /dev/ or /run/"
                continue
            fi
            # The leading '.' is crucial to create the parent directories inside the current working directory ROOTFS_DIR
            # and to copy the symlink target into the current working directory ROOTFS_DIR:
            mkdir $v -p .$( dirname $link_target ) || LogPrintError "Failed to make parent directories for symlink target '$link_target'"
            # Continue even after "Failed to make parent directories for symlink target ..." and let 'cp' also fail
            # to also show the explicit "Failed to copy symlink target ..." message to the user:
            cp $v --preserve=all $link_target .$link_target || LogPrintError "Failed to copy target of symlink '$broken_symlink' -> '$link_target'"
        else
            LogPrintError "Broken symlink '$broken_symlink' in recovery system because 'readlink' cannot determine its link target"
        fi
    done
popd

MR SKB