From 9a884151852eafa00889e414b381b3defbf1be16 Mon Sep 17 00:00:00 2001
From: Andrew Cady <d@cryptonomic.net>
Date: Thu, 29 Oct 2020 22:52:19 -0400
Subject: btrfs-shrink: support shrinking the .patch.btrfs

---
 btrfs-shrink | 37 ++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/btrfs-shrink b/btrfs-shrink
index 1d059ff..a9bbee7 100755
--- a/btrfs-shrink
+++ b/btrfs-shrink
@@ -6,7 +6,7 @@ shrink()
 {
     local shrinkmegs=100 mountpoint="$1"
     while true; do
-        while ! btrfs filesystem resize -${shrinkmegs}M "$mountpoint"/; do
+        while ! btrfs filesystem resize "${DEVICE_ID}:-${shrinkmegs}M" "$mountpoint"/; do
             shrinkmegs=$((shrinkmegs - 10 ))
             if [ $shrinkmegs -lt 10 ]; then
                 return
@@ -18,47 +18,42 @@ shrink()
 smart_shrink()
 {
     local min_dev_size mountpoint="$1"
-    if min_dev_size=$(btrfs inspect-internal min-dev-size --id 1 "$mountpoint") && [ "$min_dev_size" ]
+    if min_dev_size=$(btrfs inspect-internal min-dev-size --id "$DEVICE_ID" "$mountpoint") && [ "$min_dev_size" ]
     then
         set -- $min_dev_size
         [ "$2" = bytes ] || die "Unexpected output from btrfs inspect-internal min-dev-size: '$min_dev_size'"
-        btrfs filesystem resize "$1" "$mountpoint" && return
+        btrfs filesystem resize "$DEVICE_ID:$1" "$mountpoint" && return
     fi
     shrink "$mountpoint"
 }
 
-btrfs_truncate()
-{
-    local img="$1" bytes
-#   548044800/1176715264 bytes used
-    bytes=$(file "$img" | sed -ne 's?.*/\([0-9]*\) bytes used.*?\1?p')
-    if [ "$bytes" ]; then
-        truncate -s "$bytes" "$img"
-    fi
-}
-
-parse_btrfs_dev_size()
+parse_btrfs_dev()
 {
     local dev="$1"
-    sed -n 's?.* size \([0-9]*\) .* path \([^ ]*\)$?\1 \2? p' |
-        while read size name
+    sed -n 's?^	devid *\([0-9]*\) size \([0-9]*\) .* path \([^ ]*\)$?\1 \2 \3? p' |
+        while read devid size name
         do [ "$name" = "$dev" ] || continue
-           echo $size
+           echo "$devid $size"
            break
         done
 }
 
-get_truncate_size()
+get_btrfs_dev()
 {
     local imgfile="$1" mountpoint="$2" loop_dev dev_size
+    losetup -nj "$imgfile" >&2
     loop_dev=$(losetup -ONAME --raw -nj "$imgfile")
-    btrfs fi sh --raw "$mountpoint" | parse_btrfs_dev_size "$loop_dev"
+    ds=$(btrfs fi sh --raw "$mountpoint" | parse_btrfs_dev "$loop_dev")
+    [ "$ds" ] || return
+    DEVICE_ID=${ds% *}
+    DEVICE_SIZE=${ds#* }
 }
 
 main()
 {
     [ "$(id -u)" = 0 ] || die 'you are not root'
     if [ -d "$1" ]; then
+        exit 1
         mountpoint=$1
         mountpoint -q "$mountpoint" || die "not a mountpoint: $1"
         smart_shrink "$mountpoint"
@@ -70,11 +65,11 @@ main()
         result=$?
 
         if [ $result = 0 ]; then
-            smart_shrink "$mountpoint"
+            get_btrfs_dev "$1" "$mountpoint" && smart_shrink "$mountpoint"
             result=$?
             if [ $result = 0 ]
             then
-                truncate=$(get_truncate_size "$1" "$mountpoint")
+                get_btrfs_dev "$1" "$mountpoint" && truncate=$DEVICE_SIZE
             fi
             umount "$mountpoint"
         fi
-- 
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