From c390570e95a6457ae6af794db7fd6d49e7a4d6d2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vin=C3=ADcius=20Ferr=C3=A3o?=
 <2031761+viniciusferrao@users.noreply.github.com>
Date: Sun, 23 Aug 2026 20:59:34 -0300
Subject: [PATCH] fix(mknb): compress the genesis image with xz when lzma is
 absent

The genesis image goes into a file whose name ends with .lzma. The plugin
writes that file only when /usr/bin/lzma is there, and it falls back to gzip
when it is not.

Red Hat ships no lzma binary. On AlmaLinux 9 and on AlmaLinux 10 that test
fails, the plugin falls back to gzip, and it gives no message that says why.
The image is larger on each run of mknb. Debian and Ubuntu ship lzma as a
second name for xz, so those systems still get the smaller image.

Ask xz for the same container when lzma is absent. The command
"xz --format=lzma" writes the same bytes as "lzma", so the file keeps its
name, its container and its size. Keep the gzip fallback for a system that
has neither program.

Recovered from the lenovobuild branch, which asked xz for the xz container.
That container is not the lzma container, and the name of the file says lzma.
---
 xCAT-server/lib/xcat/plugins/mknb.pm | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/xCAT-server/lib/xcat/plugins/mknb.pm b/xCAT-server/lib/xcat/plugins/mknb.pm
index 21253dd49..b385f0698 100644
--- a/xCAT-server/lib/xcat/plugins/mknb.pm
+++ b/xCAT-server/lib/xcat/plugins/mknb.pm
@@ -246,6 +246,13 @@ sub _install_prebuilt_genesis {
     return ("$destination_dir/genesis.fs.$arch.gz", undef);
 }
 
+sub genesis_lzma_command {
+    my ($have_lzma, $have_xz) = @_;
+    return 'lzma -C crc32 -9'             if $have_lzma;
+    return 'xz --format=lzma -C crc32 -9' if $have_xz;
+    return;
+}
+
 sub process_request {
     my $request  = shift;
     my $callback = shift;
@@ -484,9 +491,10 @@ sub process_request {
         # place, so concurrent mknb runs sharing $tftpdir cannot read or clobber
         # a half-written genesis.fs.
         my $suffix = xCAT::Utils::genpassword(24);
-        if (-x "/usr/bin/lzma") {    #let's reclaim some of that size...
+        my $lzma_command = genesis_lzma_command(-x "/usr/bin/lzma", -x "/usr/bin/xz");
+        if ($lzma_command) {    #let's reclaim some of that size...
             $callback->({ data => ["Creating genesis.fs.$arch.lzma in $tftpdir/xcat"] });
-            system("cd $tempdir; find . | cpio -o -H newc | lzma -C crc32 -9 > $tftpdir/xcat/genesis.fs.$arch.lzma.$suffix");
+            system("cd $tempdir; find . | cpio -o -H newc | $lzma_command > $tftpdir/xcat/genesis.fs.$arch.lzma.$suffix");
             $lzma_exit_value = $? >> 8;
             if ($lzma_exit_value) {
                 $callback->({ data => ["Creating genesis.fs.$arch.lzma in $tftpdir/xcat failed, falling back to gzip"] });