A perl script that outputs excludes for all mount points that affect

the supplied source dir (or all mount points if the arg is omitted).
The excludes are appropriately anchored relative to the supplied dir,
and honor rsync's trailing-slash idiom.

diff --git a/support/mnt-excl b/support/mnt-excl
new file mode 100755 (executable)
index 0000000..7597f63
--- /dev/null
+++ b/support/mnt-excl
@@ -0,0 +1,35 @@
+#!/usr/bin/perl -w
+# This script takes a command-line arg of a source directory
+# that will be passed to rsync, and generates a set of excludes
+# that will exclude all mount points from the list.  This is
+# useful if you have "bind" mounts since the --one-file-system
+# option won't notice the transition to a different spot on
+# the same disk.  For example:
+#
+# mnt-excl /dir | rsync --exclude-from=- ... /dir /dest/
+# mnt-excl /dir/ | rsync --exclude-from=- ... /dir/ /dest/
+#
+# Imagine that /dir/foo is a mount point: the first invocation of
+# mnt-excl would have output /dir/foo, while the second would have
+# output /foo (which are the properly anchored excludes).
+#
+# NOTE:  This script expects /proc/mounts to exist, but could be
+# easily adapted to read /etc/mtab or similar.
+
+use strict;
+use Cwd 'abs_path';
+
+my $dir = shift || '/';
+$dir = abs_path($dir);
+$dir =~ s#([^/]*)$##;
+my $trailing = $1;
+$trailing = '' if $trailing eq '.' || !-d "$dir$trailing";
+$trailing .= '/' if $trailing ne '';
+
+open(IN, '/proc/mounts') or die $!;
+while (<IN>) {
+    $_ = (split)[1];
+    next unless s#^\Q$dir$trailing\E##o && $_ ne '';
+    print "- /$trailing$_\n";
+}
+close IN;