From 51e1865d25f971b38a492e55d6b37f7ef141c141 Mon Sep 17 00:00:00 2001
From: Andrew Cady <d@jerkface.net>
Date: Thu, 4 Mar 2021 15:50:41 -0500
Subject: initial commit

---
 Makefile    |  6 +++++
 btrfs_mount | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 Makefile
 create mode 100755 btrfs_mount

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..645e09a
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,6 @@
+all:
+
+sudo = $(shell [ $$(id -u) = 0 ] || echo sudo)
+
+install:
+	$(sudo) install btrfs_mount -t /sbin
diff --git a/btrfs_mount b/btrfs_mount
new file mode 100755
index 0000000..50303d1
--- /dev/null
+++ b/btrfs_mount
@@ -0,0 +1,74 @@
+#!/bin/dash
+
+usage()
+{
+    echo "usage: $0 [--unscan] [btrfs options] <btrfs filesystem> <mountpoint>"
+}
+
+get_prop()
+{
+    local prop="$1"
+    btrfs inspect-internal dump-super "$2" | sed -E -ne "s/^${prop}	+//p"
+}
+
+device_count()
+{
+    btrfs inspect-internal dump-super "$1" | grep -c '^dev_item.devid	'
+}
+
+competing_devices()
+{
+    local uuid
+    uuid=$1
+    btrfs filesystem show "$uuid" | sed -E -ne 's/^    devid.* //p'
+}
+
+remove_competition()
+{
+    competing_devices "$1" | while read dev
+    do
+        [ "$dev" = "$source" ] || btrfs device scan -u "$dev" || true
+    done
+}
+
+getend()
+{
+    eval "echo \${$(($#-$1))}"
+}
+
+btrfs_mount()
+{
+    [ $# -ge 2 ] || { usage; exit 1; }
+
+    destdir=$(getend 0 "$@")
+    source=$(getend 1 "$@")
+
+    [ -e "$source" ]
+    [ -r "$source" ]
+    [ -d "$destdir" ]
+
+    for args
+    do
+        case "$1" in
+                --unscan) unscan=y;;
+                *) set -- "$@" "$1";;
+        esac
+        shift
+    done
+
+    if [ "$unscan" ]
+    then
+        device_count=$(device_count "$source")
+        if [ $device_count -eq 1 ]
+        then
+            source_uuid=$(get_prop fsid "$source")
+            remove_competition "$source_uuid"
+        fi
+    fi
+
+    mount "$@"
+}
+
+set -e
+
+btrfs_mount "$@"
-- 
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