1 files changed, 52 insertions, 0 deletions

diff --git a/src/btrfs-utils/btrfs-shrink b/src/btrfs-utils/btrfs-shrink
new file mode 100755
index 0000000..f3dbbb0
--- /dev/null
+++ b/src/btrfs-utils/btrfs-shrink
@@ -0,0 +1,52 @@
+#!/bin/sh
+
+die() { printf "%s: Error: %s\n" "$0" "$*" >&2; exit 1; }
+
+[ "$(id -u)" = 0 ] || die 'you are not root'
+
+shrink()
+{
+    shrinkmegs=100
+    while true; do
+        while ! btrfs filesystem resize -${shrinkmegs}M "$mountpoint"/; do
+            shrinkmegs=$((shrinkmegs - 10 ))
+            if [ $shrinkmegs -lt 10 ]; then
+                return
+            fi
+        done
+    done
+}
+
+btrfs_truncate()
+{
+    local img="$1" bytes
+    bytes=$(file "$img" | sed -ne 's?.*/\([0-9]*\)/[0-9]* bytes used.*?\1?p')
+#   548044800/1176715264 bytes used
+    if [ "$bytes" ]; then
+        truncate -s "$bytes" "$img"
+    fi
+}
+
+main()
+{
+    if [ -d "$1" ]; then
+        mountpoint -q "$1" || die "not a mountpoint: $1"
+        shrink "$1"
+    elif [ -f "$1" ]; then
+        mkdir "$1".mnt.tmp
+        mount -t btrfs "$1" "$1".mnt.tmp
+        result=$?
+        if [ $result = 0 ]; then
+            shrink "$1".mnt.tmp
+            result=$?
+        fi
+        umount "$1".mnt.tmp
+        rmdir "$1".mnt.tmp
+        btrfs_truncate "$1"
+        return $result
+    else
+        die "not a file or directory: $1"
+    fi
+}
+
+main "$@"