From ce4bfa5d0800660a8593593d73e2b626563e4cfe Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Tue, 17 Mar 2026 14:44:53 +0000
Subject: [PATCH] lib: Add get_default_hv to backend operations

Add a generic way for backends to report the default hypervisor
(ie. QEMU) back to the main code.

The direct implemention reflects the current way that the hypervisor
is chosen at configure time (see m4/guestfs-qemu.m4).

For the libvirt backend, we are already getting this from libvirt
domcapabilities, so we can just return that field.

Note this may return NULL (roughly "no data"), particularly in the
libvirt case because that requires us to have launched the appliance
already.
---
 lib/guestfs-internal.h |  5 +++++
 lib/launch-direct.c    | 18 ++++++++++++++++++
 lib/launch-libvirt.c   |  8 ++++++++
 3 files changed, 31 insertions(+)

diff --git a/lib/guestfs-internal.h b/lib/guestfs-internal.h
index c20564e98..7c5bf4dd7 100644
--- a/lib/guestfs-internal.h
+++ b/lib/guestfs-internal.h
@@ -331,6 +331,11 @@ struct backend_ops {
    */
   char *(*create_cow_overlay) (guestfs_h *g, void *data, struct drive *drv);
 
+  /* Get the default hypervisor (qemu), if the user does not override
+   * this by calling guestfs_set_hv or setting LIBGUESTFS_HV.
+   */
+  const char *(*get_default_hv) (guestfs_h *g, void *data);
+
   /* Launch and shut down. */
   int (*launch) (guestfs_h *g, void *data, const char *arg);
   int (*shutdown) (guestfs_h *g, void *data, int check_for_errors);
diff --git a/lib/launch-direct.c b/lib/launch-direct.c
index caaadd420..d56127f98 100644
--- a/lib/launch-direct.c
+++ b/lib/launch-direct.c
@@ -441,6 +441,23 @@ free_pid_path:
   return rc;
 }
 
+/* Pick a default, arch-specific qemu. */
+static const char *
+get_default_hv_direct (guestfs_h *g, void *datav)
+{
+  if (host_cpu[0] == 'i' && strchr ("3456", host_cpu[1]) &&
+      host_cpu[2] == '8' && host_cpu[3] == '6' && host_cpu[4] == '\0')
+    return "qemu-system-i386";
+  else if (STRPREFIX (host_cpu, "arm"))
+    return "qemu-system-arm";
+  else if (STREQ (host_cpu, "powerpc64") ||
+           STREQ (host_cpu, "powerpc64le") ||
+           STREQ (host_cpu, "ppc64le"))
+    return "qemu-system-ppc64";
+  else
+    return "qemu-system-" host_cpu;
+}
+
 static int
 launch_direct (guestfs_h *g, void *datav, const char *arg)
 {
@@ -1105,6 +1122,7 @@ max_disks_direct (guestfs_h *g, void *datav)
 static struct backend_ops backend_direct_ops = {
   .data_size = sizeof (struct backend_direct_data),
   .create_cow_overlay = create_cow_overlay_direct,
+  .get_default_hv = get_default_hv_direct,
   .launch = launch_direct,
   .shutdown = shutdown_direct,
   .get_pid = get_pid_direct,
diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c
index d12fc24c7..eb28b86c7 100644
--- a/lib/launch-libvirt.c
+++ b/lib/launch-libvirt.c
@@ -305,6 +305,13 @@ create_cow_overlay_libvirt (guestfs_h *g, void *datav, struct drive *drv)
   return overlay;
 }
 
+static const char *
+get_default_hv_libvirt (guestfs_h *g, void *datav)
+{
+  struct backend_libvirt_data *data = datav;
+  return data->default_qemu;
+}
+
 static int
 launch_libvirt (guestfs_h *g, void *datav, const char *libvirt_uri)
 {
@@ -2211,6 +2218,7 @@ max_disks_libvirt (guestfs_h *g, void *datav)
 static struct backend_ops backend_libvirt_ops = {
   .data_size = sizeof (struct backend_libvirt_data),
   .create_cow_overlay = create_cow_overlay_libvirt,
+  .get_default_hv = get_default_hv_libvirt,
   .launch = launch_libvirt,
   .shutdown = shutdown_libvirt,
   .max_disks = max_disks_libvirt,