1#!/bin/sh
2#
3# Perform a bind mount, copying existing files as we do so to ensure the
4# overlaid path has the necessary content.
5# If the target is a directory and overlayfs is available (and the environment
6# variable MOUNT_COPYBIND_AVOID_OVERLAYFS=1 is not set), then an overlay mount
7# will be attempted first.
8
9if [ $# -lt 2 ]; then
10    echo >&2 "Usage: $0 spec mountpoint [OPTIONS]"
11    exit 1
12fi
13
14# e.g. /var/volatile/lib
15spec=$1
16
17# e.g. /var/lib
18mountpoint=$2
19
20if [ $# -gt 2 ]; then
21    options=$3
22else
23    options=
24fi
25
26[ -n "$options" ] && options=",$options"
27
28mkdir -p "${spec%/*}"
29
30if [ -d "$mountpoint" ]; then
31
32    if [ -d "$spec" ]; then
33        specdir_existed=yes
34    else
35        specdir_existed=no
36        mkdir "$spec"
37        # If the $spec directory is created we need to take care that
38        # the selinux context is correct
39        if command -v selinuxenabled > /dev/null 2>&1; then
40            if selinuxenabled; then
41                restorecon "$spec"
42            fi
43        fi
44    fi
45
46    # Fast version of calculating `dirname ${spec}`/.`basename ${spec}`-work
47    overlay_workdir="${spec%/*}/.${spec##*/}-work"
48    mkdir "${overlay_workdir}"
49
50    # Try to mount using overlay, which is must faster than copying files.
51    # If that fails, fall back to slower copy.
52    if command -v selinuxenabled > /dev/null 2>&1; then
53        if selinuxenabled; then
54            mountcontext=",rootcontext=$(matchpathcon -n "$mountpoint")"
55        fi
56    fi
57    if [ "$MOUNT_COPYBIND_AVOID_OVERLAYFS" = 1 ] || ! mount -t overlay overlay -olowerdir="$mountpoint",upperdir="$spec",workdir="$overlay_workdir""$mountcontext" "$mountpoint" > /dev/null 2>&1; then
58
59        if [ "$specdir_existed" != "yes" ]; then
60            cp -aPR "$mountpoint"/. "$spec/"
61        fi
62
63        mount -o "bind$options" "$spec" "$mountpoint"
64        # restore the selinux context.
65        if command -v selinuxenabled > /dev/null 2>&1; then
66            if selinuxenabled; then
67                restorecon -R "$mountpoint"
68            fi
69        fi
70    fi
71elif [ -f "$mountpoint" ]; then
72    if [ ! -f "$spec" ]; then
73        cp -aP "$mountpoint" "$spec"
74    fi
75
76    mount -o "bind$options" "$spec" "$mountpoint"
77    # restore the selinux context.
78    if command -v selinuxenabled > /dev/null 2>&1; then
79        if selinuxenabled; then
80            restorecon -R "$mountpoint"
81        fi
82    fi
83fi
84