gnu: spice-vdagent: Apply a patch fixing the monitor size calculation.

This fixes errors like:

   spice-vdagentd[870]: invalid message size for VDAgentMonitorsConfig

See: <https://github.com/utmapp/UTM/issues/5832#issuecomment-3194879161>

* gnu/packages/patches/spice-vdagent-monitor-size-calculation.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/spice.scm (spice-vdagent) [source] <patches>: New field.

Change-Id: I4bc0f8e207bef65c8f2fcd64928315825d520ad1

gnu/local.mk

@@ -2331,6 +2331,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/softhsm-fix-openssl3-tests.patch		\
   %D%/packages/patches/spectre-meltdown-checker-externalize-fwdb.patch \
   %D%/packages/patches/sphinxbase-fix-doxygen.patch		\
+  %D%/packages/patches/spice-vdagent-monitor-size-calculation.patch     \
   %D%/packages/patches/guile-srfi-125-fix-r7rs-rename-clause.patch \
   %D%/packages/patches/sssd-system-directories.patch		\
   %D%/packages/patches/steghide-fixes.patch			\

gnu/packages/patches/spice-vdagent-monitor-size-calculation.patch

@@ -0,0 +1,29 @@
+From 3660acfcbaaca9c66dca5ef09205bd7c1d70b98c Mon Sep 17 00:00:00 2001
+From: Lukas Joeressen <lukas@joeressen.net>
+Date: Sat, 12 Apr 2025 10:42:02 +0200
+Subject: [PATCH] Fix VDAGentMonitorConfig size calculation
+
+The VDAgentMonitorsConfig struct has the VD_AGENT_CONFIG_MONITORS_FLAG_PHYSICAL_SIZE flag that
+indicates if physical monitor sizes are included in the data. If this flag is set there is one
+instance of VDAgentMonitorMM for each monitor following the other data.
+---
+ src/vdagentd/vdagentd.c | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/src/vdagentd/vdagentd.c b/src/vdagentd/vdagentd.c
+index 3e59331..27a6f15 100644
+--- a/src/vdagentd/vdagentd.c
++++ b/src/vdagentd/vdagentd.c
+@@ -208,6 +208,9 @@ static void do_client_monitors(VirtioPort *vport, int port_nr,
+     /* Store monitor config to send to agents when they connect */
+     size = sizeof(VDAgentMonitorsConfig) +
+            new_monitors->num_of_monitors * sizeof(VDAgentMonConfig);
++    if (new_monitors->flags & VD_AGENT_CONFIG_MONITORS_FLAG_PHYSICAL_SIZE) {
++        size += new_monitors->num_of_monitors * sizeof(VDAgentMonitorMM);
++    }
+     if (message_header->size != size) {
+         syslog(LOG_ERR, "invalid message size for VDAgentMonitorsConfig");
+         return;
+-- 
+GitLab
+

gnu/packages/spice.scm

@@ -293,7 +293,10 @@ Internet and from a wide variety of machine architectures.")
                     "spice-vdagent-" version ".tar.bz2"))
               (sha256
                (base32
-                "18472sqr0gibzgzi48dpcbnvm78l05qrl5wv6xywqqj7r9dd3c4k"))))
+                "18472sqr0gibzgzi48dpcbnvm78l05qrl5wv6xywqqj7r9dd3c4k"))
+              (patches
+               (search-patches
+                "spice-vdagent-monitor-size-calculation.patch"))))
     (build-system gnu-build-system)
     (arguments
      `(#:configure-flags