From 3a1a19b39bb79cb76483538c1acbb7aa94a9064a Mon Sep 17 00:00:00 2001
From: Christoph Klaffl <christoph@phreaker.eu>
Date: Wed, 18 Feb 2026 14:57:38 +0100
Subject: [PATCH] fix replication with '0' named bookmarks

---
 syncoid                                       |  8 ++--
 .../013_bookmark_replication_0_named/run.sh   | 48 +++++++++++++++++++
 2 files changed, 52 insertions(+), 4 deletions(-)
 create mode 100755 tests/syncoid/013_bookmark_replication_0_named/run.sh

diff --git a/syncoid b/syncoid
index 8c9c2f2..945e095 100755
--- a/syncoid
+++ b/syncoid
@@ -575,7 +575,7 @@ sub syncdataset {
 
 		my $targetsize = getzfsvalue($targethost,$targetfs,$targetisroot,'-p used');
 
-		my $bookmark = 0;
+		my $bookmark = '';
 		my $bookmarkcreation = 0;
 
 		$matchingsnap = getmatchingsnapshot($sourcefs, $targetfs, \%snaps);
@@ -596,7 +596,7 @@ sub syncdataset {
 				}
 			}
 
-			if (! $bookmark) {
+			if ($bookmark eq '') {
 				# force delete is not possible for the root dataset
 				if ($args{'force-delete'} && index($targetfs, '/') != -1) {
 					writelog('INFO', "Removing $targetfs because no matching snapshots were found");
@@ -669,7 +669,7 @@ sub syncdataset {
 
 			my $nextsnapshot = 0;
 
-			if ($bookmark) {
+			if ($bookmark ne '') {
 				my $bookmarkescaped = escapeshellparam($bookmark);
 
 				if (!defined $args{'no-stream'}) {
@@ -727,7 +727,7 @@ sub syncdataset {
 			# do a normal replication if bookmarks aren't used or if previous
 			# bookmark replication was only done to the next oldest snapshot
 			# edge case: skip repilcation if bookmark replication used the latest snapshot
-			if ((!$bookmark || $nextsnapshot) && !($matchingsnap eq $newsyncsnap)) {
+			if (($bookmark eq '' || $nextsnapshot) && !($matchingsnap eq $newsyncsnap)) {
 
 				($exit, $stdout) = syncincremental($sourcehost, $sourcefs, $targethost, $targetfs, $matchingsnap, $newsyncsnap, defined($args{'no-stream'}));
 
diff --git a/tests/syncoid/013_bookmark_replication_0_named/run.sh b/tests/syncoid/013_bookmark_replication_0_named/run.sh
new file mode 100755
index 0000000..f811e56
--- /dev/null
+++ b/tests/syncoid/013_bookmark_replication_0_named/run.sh
@@ -0,0 +1,48 @@
+#!/bin/bash
+
+# test replication with fallback to bookmarks and special named snapshot/bookmark '0'
+
+set -x
+set -e
+
+. ../../common/lib.sh
+
+POOL_IMAGE="/tmp/syncoid-test-013.zpool"
+POOL_SIZE="200M"
+POOL_NAME="syncoid-test-013"
+TARGET_CHECKSUM="b927125d2113c8da1a7f0181516e8f57fee5d268bdd5386d6ff7ddf31d6d6a35  -"
+
+truncate -s "${POOL_SIZE}" "${POOL_IMAGE}"
+
+zpool create -m none -f "${POOL_NAME}" "${POOL_IMAGE}"
+
+function cleanUp {
+  zpool export "${POOL_NAME}"
+}
+
+# export pool in any case
+trap cleanUp EXIT
+
+zfs create "${POOL_NAME}"/src
+zfs snapshot "${POOL_NAME}"/src@0
+
+# initial replication
+../../../syncoid --no-sync-snap --create-bookmark --debug --compress=none "${POOL_NAME}"/src "${POOL_NAME}"/dst
+
+# destroy last common snapshot on source
+zfs destroy "${POOL_NAME}"/src@0
+
+zfs snapshot "${POOL_NAME}"/src@1
+
+# replicate which should fallback to bookmarks
+../../../syncoid --no-sync-snap --create-bookmark --debug --compress=none "${POOL_NAME}"/src "${POOL_NAME}"/dst
+
+# verify
+output=$(zfs list -t snapshot -r -H -o name "${POOL_NAME}"; zfs list -t bookmark -r -H -o name "${POOL_NAME}")
+checksum=$(echo "${output}" | grep -v syncoid_ | shasum -a 256)
+
+if [ "${checksum}" != "${TARGET_CHECKSUM}" ]; then
+	exit 1
+fi
+
+exit 0