Strip down to just bsnap

[monosys] / bsnap

diff --git a/bsnap b/bsnap
new file mode 100755 (executable)
index 0000000..1f36d8e
--- /dev/null
+++ b/bsnap
@@ -0,0 +1,124 @@
+#!/bin/bash
+
+set -eu
+
+function snap {
+    unsnap
+
+    mkdir -p /a
+
+    dispatch snap < /etc/fstab
+}
+
+function unsnap {
+    tac /etc/fstab | dispatch unsnap
+
+    if [ -d "/a" ]; then
+        rmdir /a
+    fi
+}
+
+function dispatch {
+    local action="" snaptype=""
+    local dev="" mnt="" fstype="" opts="" dump=""
+
+    while read -r dev mnt fstype opts dump pass; do
+        snaptype="$(get_snaptype "$fstype" "$dump")"
+        if [ -z "$snaptype" ]; then
+            continue
+        fi
+        action="${1}_${snaptype}"
+        echo "$action $mnt"
+        "$action" "$dev" "$mnt" "$opts"
+    done
+}
+
+function get_snaptype {
+    local fstype="$1" dump="$2"
+    if [ "$dump" = "1" ]; then
+        echo bind
+    elif [ "$dump" = "2" ] && [ "$fstype" = "btrfs" ]; then
+        echo btrfs
+    elif [ "$dump" = "2" ]; then
+        echo lvm
+    fi
+}
+
+function snap_bind {
+    local mnt="$2"
+    mount --bind "${mnt}" "/a${mnt}"
+}
+
+function unsnap_bind {
+    local snapmnt="/a$2"
+    if mountpoint -q "$snapmnt"; then
+        umount "$snapmnt"
+    fi
+}
+
+function snap_lvm {
+    local dev="$1" mnt="$2"
+    local lvname="" vgname=""
+    read -r lvname vgname _ < <(lvdisplay --noheadings -C "$dev")
+    echo "snapshot ${vgname}/${lvname}"
+    lvcreate -L1G --snapshot --name "${lvname}snap" "${vgname}/${lvname}"
+    mount -o ro "${dev}snap" "/a${mnt}"
+}
+
+function unsnap_lvm {
+    local snapdev="${1}snap"
+    local snapmnt="/a$2"
+    if mountpoint -q "$snapmnt"; then
+        umount "$snapmnt"
+    fi
+    if [ -b "$(readlink -f "$snapdev")" ]; then
+        lvremove -f "${dev}snap"
+    fi
+}
+
+function snap_btrfs {
+    local mnt="$2" opts="$3" snapdir=""
+
+    snapdir="$(get_btrfs_snapshot_dir "$opts" "$mnt")"
+    btrfs subvolume snapshot "$mnt" "$snapdir"
+
+    mount --bind "$snapdir" "/a${mnt}"
+}
+
+function unsnap_btrfs {
+    local mnt="$2" opts="$3" snapdir=""
+
+    local snapmnt="/a$2"
+    if mountpoint -q "$snapmnt"; then
+        umount "$snapmnt"
+    fi
+
+    snapdir="$(get_btrfs_snapshot_dir "$opts" "$mnt")"
+    if [ -d "$snapdir" ]; then
+        btrfs subvolume delete "$snapdir"
+    fi
+}
+
+function get_btrfs_snapshot_dir {
+    local opts="$1" mnt="$2" subvol=""
+    subvol="$(echo "$opts" | sed -nE 's/^.*\bsubvol=([^,]+)\b.*$/\1/p')"
+    if [ -z "$subvol" ]; then
+        echo "Unknown subvol for mountpoint: $mnt"
+        exit 1
+    fi
+    echo "/$(hostname -s)/${subvol}-snap"
+}
+
+if [ "$(id -u)" -ne 0 ]; then
+    echo "Must be root"
+    exit 1
+fi
+
+if [ "${1:-}" = "off" ]; then
+    unsnap
+elif [ "${1:-}" = "on" ]; then
+    snap
+else
+    echo "Usage: $0 on|off"
+    exit 1
+fi