Libguestfs - Mar 2021 - [PATCH libguestfs 0/1] Introduce force_kvm backend

When we want to make sure that libguestfs runs in a performant
environemnt, it is useful to have such flag - otherwise we can't rely on
libguestfs not to fall back to use tcg.

Sam Eiderman (1):
  launch: libvirt,direct: Add force_tcg backend setting.

 lib/launch-direct.c  | 22 +++++++++++++++++++---
 lib/launch-libvirt.c | 12 +++++++++++-
 2 files changed, 30 insertions(+), 4 deletions(-)

-- 
2.31.0.rc2.261.g7f71774620-goog

By using:

  export LIBGUESTFS_BACKEND_SETTINGS=force_kvm

you can force the backend to use KVM and never fall back to
TCG (software emulation).
---
 lib/launch-direct.c  | 22 +++++++++++++++++++---
 lib/launch-libvirt.c | 12 +++++++++++-
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/lib/launch-direct.c b/lib/launch-direct.c
index b6ed9766f..79e6ef2fd 100644
--- a/lib/launch-direct.c
+++ b/lib/launch-direct.c
@@ -385,6 +385,7 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   struct hv_param *hp;
   bool has_kvm;
   int force_tcg;
+  int force_kvm;
   const char *cpu_model;
   CLEANUP_FREE char *append = NULL;
   CLEANUP_FREE_STRING_LIST char **argv = NULL;
@@ -434,8 +435,22 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   if (force_tcg == -1)
     return -1;
 
-  if (!has_kvm && !force_tcg)
-    debian_kvm_warning (g);
+  force_kvm = guestfs_int_get_backend_setting_bool (g, "force_kvm");
+  if (force_kvm == -1)
+    return -1;
+
+  if (force_kvm && force_tcg) {
+    error (g, "Both force_kvm and force_tcg backend settings
supplied.");
+    return -1;
+  }
+  if (!has_kvm) {
+    if (!force_tcg)
+      debian_kvm_warning (g);
+    if (force_kvm) {
+      error (g, "force_kvm supplied but kvm not available.");
+      return -1;
+    }
+  }
 
   /* Using virtio-serial, we need to create a local Unix domain socket
    * for qemu to connect to.
@@ -530,7 +545,8 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
     if (has_kvm && !force_tcg)
       append_list ("gic-version=host");
 #endif
-    append_list_format ("accel=%s", !force_tcg ? "kvm:tcg"
: "tcg");
+    append_list_format ("accel=%s", force_kvm ? "kvm" :
+                                    (!force_tcg ? "kvm:tcg" :
"tcg"));
   } end_list ();
 
   cpu_model = guestfs_int_get_cpu_model (has_kvm && !force_tcg);
diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c
index 6c0cfe937..a56afbdd4 100644
--- a/lib/launch-libvirt.c
+++ b/lib/launch-libvirt.c
@@ -773,6 +773,7 @@ parse_capabilities (guestfs_h *g, const char
*capabilities_xml,
   xmlAttrPtr attr;
   size_t seen_qemu, seen_kvm;
   int force_tcg;
+  int force_kvm;
 
   doc = xmlReadMemory (capabilities_xml, strlen (capabilities_xml),
                        NULL, NULL, XML_PARSE_NONET);
@@ -820,11 +821,15 @@ parse_capabilities (guestfs_h *g, const char
*capabilities_xml,
     }
   }
 
+  force_kvm = guestfs_int_get_backend_setting_bool (g, "force_kvm");
+  if (force_kvm == -1)
+    return -1;
+
   /* This was RHBZ#886915: in that case the default libvirt URI
    * pointed to a Xen hypervisor, and so could not create the
    * appliance VM.
    */
-  if (!seen_qemu && !seen_kvm) {
+  if ((!seen_qemu || force_kvm) && !seen_kvm) {
     CLEANUP_FREE char *backend = guestfs_get_backend (g);
 
     error (g,
@@ -846,6 +851,11 @@ parse_capabilities (guestfs_h *g, const char
*capabilities_xml,
   if (force_tcg == -1)
     return -1;
 
+  if (force_kvm && force_tcg) {
+    error (g, "Both force_kvm and force_tcg backend settings
supplied.");
+    return -1;
+  }
+
   if (!force_tcg)
     data->is_kvm = seen_kvm;
   else
-- 
2.31.0.rc2.261.g7f71774620-goog