server: Fix .zero fallback path

resolves: RHEL-101635

0044-server-Fix-.zero-fallback-path.patch

@@ -0,0 +1,39 @@
+From e947a2a55cb018711b7f4ede5b5cec291ed5cf24 Mon Sep 17 00:00:00 2001
+From: "Richard W.M. Jones" <rjones@redhat.com>
+Date: Wed, 2 Jul 2025 16:18:19 +0100
+Subject: [PATCH] server: Fix .zero fallback path
+
+When no efficient zero method is supported, we fall back to writing a
+buffer of actual zeroes.  However because of an omitted update to
+'offset' we would only zero out (up to) the first 64M of each range.
+nbdcopy defaults to working on blocks of 128M, leaving the second 64M
+unzeroed.
+
+This affects only backing filesystems which do not support fallocate
+FALLOC_FL_PUNCH_HOLE or FALLOC_FL_ZERO_RANGE, which turns out to be
+rare, but it does include some NFS-mounted filesystems which is where
+I saw this problem.
+
+Fixes: commit 19184d3eb6356ae3b14da0fbaa9c9bdc7743a448
+Thanks: Alex Kalenyuk
+(cherry picked from commit 20b23fc9838faeddfd42664a7f497a9b29dc5921)
+(cherry picked from commit 3c8d0812e7a7b6a1f9e5cceab7bee6e25b9cd7cd)
+---
+ server/plugins.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/server/plugins.c b/server/plugins.c
+index 3c7df0d2..db36ce42 100644
+--- a/server/plugins.c
++++ b/server/plugins.c
+@@ -807,6 +807,7 @@ plugin_zero (struct context *c,
+     if (r == -1)
+       break;
+     count -= limit;
++    offset += limit;
+   }
+ 
+  done:
+-- 
+2.47.1
+

nbdkit.spec

@@ -56,7 +56,7 @@
 
 Name:           nbdkit
 Version:        1.38.5
-Release:        11%{?dist}
+Release:        12%{?dist}
 Summary:        NBD server
 
 License:        BSD-3-Clause
@@ -124,6 +124,7 @@ Patch0040:     0040-vddk-stats-Collect-elapsed-time-for-ReadAsync-and-Wr.patch
 Patch0041:     0041-server-Fix-off-by-one-for-maximum-block_status-lengt.patch
 Patch0042:     0042-blocksize-Fix-32-bit-overflow-in-.extents-CVE-2025-4.patch
 Patch0043:     0043-vddk-Add-support-for-VDDK-9.0.0.0.patch
+Patch0044:     0044-server-Fix-.zero-fallback-path.patch
 
 # For automatic RPM Provides generation.
 # See: https://rpm-software-management.github.io/rpm/manual/dependency_generators.html
@@ -1542,6 +1543,10 @@ fi
 
 
 %changelog
+* Sat Jul 05 2025 Richard W.M. Jones <rjones@redhat.com> - 1.38.5-12
+- server: Fix .zero fallback path
+  resolves: RHEL-101635
+
 * Mon Jun 23 2025 Richard W.M. Jones <rjones@redhat.com> - 1.38.5-11
 - Add support for VDDK 9.0.0.0
   resolves: RHEL-99466