#!/usr/bin/perl

# This script outputs data for rsyncdb --mounts.  It must output a complete
# list of the mounts for the current host in a strict format -- 2 fields
# with a Tab between:  $MOUNT_UNIQ\t$PATH
#
# The list of mounts MUST NOT contain any entry that has the same devnum
# (st_dev) as any other entry in the list (as checked via its PATH).
#
# MOUNT_UNIQ is a unique string that identifies the mount on this host.
# This cannot be the devnum (st_dev) because that can vary depending on the
# mount order or be reused for different mounts if they are not mounted at
# the same time.  Ideally this would be its UUID value, if that is available
# on this OS.  This script looks in /dev/disk/by-uuid for the current UUID
# mappings).  If the UUID is not found, the fallback default is the string
# "Mount of $devname", which should be adequate for situations that don't
# use removable media (though you may need to take steps to weed-out removable
# mounts).
#
# You can override the MOUNT_UNIQ value by putting a .rsyncdb_mount_uniq
# file in the root directory of any mount, at which point it is up to you
# to make sure that the value stays unique (note that all sequences of
# whitespace are transformed into a single space, and leading/trailing
# whitespace is removed).
#
# MOUNT_UNIQ may never contain a Tab but it would be legal for PATH to have
# a Tab (just really weird).  Neither may have a CR or LF in it.
#
# The maximum size for MOUNT_UNIQ is 256 characters.
#
# If this script doesn't meet your needs, feel free to edit/replace it and
# choose some other method of finding a unique value for each mount.  If you
# come up with a good idiom that might be useful to others, please share it
# with the rsync mailing list.

use strict;
use warnings;
use Cwd 'abs_path';

my @MOUNT_FILES = qw( /proc/mounts /etc/mtab );
my $VALID_DEVICE_REGEX = qr{^/dev|^rootfs$};
my $UUID_DIR = '/dev/disk/by-uuid';
my $OVERRIDE_FILE = '.rsyncdb_mount_uniq';

my (%hash, %uuid);

if (-d $UUID_DIR) {
    foreach my $uuid (glob "$UUID_DIR/*") {
	my $lnk = readlink($uuid);
	if ($lnk !~ m{^/}) {
	    $lnk = abs_path("$UUID_DIR/$lnk");
	}
	$uuid =~ s{.*/}{};
	$uuid{$lnk} = $uuid;
    }
}

foreach my $mount_file (@MOUNT_FILES) {
    if (open MOUNTS, $mount_file) {
	while (<MOUNTS>) {
	    my ($devname, $path) = (split)[0,1];
	    next unless $devname =~ /$VALID_DEVICE_REGEX/;

	    my ($devno) = (stat($path))[0];
	    next unless defined $devno; # Skip if mount is invalid.
	    next if $hash{$devno}++; # SKip if we've seen this devno earlier.

	    my $mount_uniq = $uuid{$devname} ? $uuid{$devname} : "Mount of $devname";
	    if (open UNIQ, '<', "$path/$OVERRIDE_FILE") {
		$mount_uniq = <UNIQ>;
		close UNIQ;
		$mount_uniq =~ s/\s+/ /g; # This ensures no tab, CR, nor LF.
		$mount_uniq =~ s/^ | $//g; # .. and no leading or trailing whitespace.
	    }
	    print $mount_uniq, "\t", $path, "\n";
	}
	close MOUNTS;
	exit;
    }
}

die "Failed to to open any mount files: @MOUNT_FILES\n";