From b8ae251afe10eac2f195fd71cb5f3efa358e213c Mon Sep 17 00:00:00 2001
From: Michal Fox <me@dualfroz.com>
Date: Fri, 2 Oct 2026 16:11:58 +0200
Subject: [PATCH] fix #7173: write config: drop empty tag list

When the last tag of a VM gets removed, for example in the web UI, the
API gets an empty 'tags' value, which then ends up as an empty 'tags:'
line in the config and in the output of 'qm config'. As the config
parser reads that line back as a single space, it also gets written out
again on every following config change.

Skip a tag list without any tag when writing the config, which also
cleans up existing configs with such a line on their next change. The
pending section still needs to keep it, otherwise the removal of all
tags would get lost between writing the pending change and applying it.

Signed-off-by: Michal Fox <me@dualfroz.com>
---
 src/PVE/QemuServer.pm                          | 2 ++
 src/test/parse-config-expected/empty-tags.conf | 8 ++++++++
 src/test/parse-config-input/empty-tags.conf    | 9 +++++++++
 src/test/run_parse_config_tests.pl             | 2 +-
 4 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 src/test/parse-config-expected/empty-tags.conf
 create mode 100644 src/test/parse-config-input/empty-tags.conf

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index f199371..3b9a86a 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -2167,6 +2167,8 @@ sub write_vm_config {
 
         foreach my $key (sort keys %$conf) {
             next if $key =~ /^(digest|description|pending|snapshots|special-sections)$/;
+            # an empty tag list is only needed as pending change for removing all tags
+            next if $key eq 'tags' && !$pending && $conf->{$key} =~ m/^\s*$/;
             $raw .= "$key: $conf->{$key}\n";
         }
         return $raw;
diff --git a/src/test/parse-config-expected/empty-tags.conf b/src/test/parse-config-expected/empty-tags.conf
new file mode 100644
index 0000000..13e82c4
--- /dev/null
+++ b/src/test/parse-config-expected/empty-tags.conf
@@ -0,0 +1,8 @@
+# empty tag list
+boot: order=scsi0
+cores: 1
+memory: 512
+name: notags
+ostype: l26
+scsi0: local-lvm:vm-100-disk-0,size=4G
+scsihw: virtio-scsi-single
diff --git a/src/test/parse-config-input/empty-tags.conf b/src/test/parse-config-input/empty-tags.conf
new file mode 100644
index 0000000..e3e09d6
--- /dev/null
+++ b/src/test/parse-config-input/empty-tags.conf
@@ -0,0 +1,9 @@
+# empty tag list
+boot: order=scsi0
+cores: 1
+memory: 512
+name: notags
+ostype: l26
+scsi0: local-lvm:vm-100-disk-0,size=4G
+scsihw: virtio-scsi-single
+tags: 
diff --git a/src/test/run_parse_config_tests.pl b/src/test/run_parse_config_tests.pl
index 62e36ee..84602e4 100644
--- a/src/test/run_parse_config_tests.pl
+++ b/src/test/run_parse_config_tests.pl
@@ -26,7 +26,7 @@ my $OUTPUT_DIR = './parse-config-output';
 my $EXPECTED_DIR = './parse-config-expected';
 
 # NOTE update when you add/remove tests
-plan tests => 2 * 10;
+plan tests => 2 * 11;
 
 sub run_tests {
     my ($strict) = @_;