[Libguestfs] [PATCH v3 libguestfs] launch: libvirt, direct: Add force_kvm backend setting.

[Sam Eiderman]

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/guestfs-internal.h |  3 +++
 lib/guestfs.pod        |  9 +++++++++
 lib/launch-direct.c    | 42 ++++++++++++++++++++++++++++++++++++------
 lib/launch-libvirt.c   | 29 ++++++++++++++++++++++++-----
 4 files changed, 72 insertions(+), 11 deletions(-)

diff --git a/lib/guestfs-internal.h b/lib/guestfs-internal.h
index 43509c6db..97dacc2b8 100644
--- a/lib/guestfs-internal.h
+++ b/lib/guestfs-internal.h
@@ -157,6 +157,9 @@ guestfs_int_cleanup_gl_recursive_lock_unlock (void *ptr)
 #define VIRTIO_DEVICE_NAME(type) type "-pci"
 #endif
 
+/* Guestfs accel options. */
+enum accel { BEST_ACCEL, FORCE_TCG, FORCE_KVM };
+
 /* Guestfs handle and associated structures. */
 
 /* State. */
diff --git a/lib/guestfs.pod b/lib/guestfs.pod
index bce9eb79f..ff58aa0bb 100644
--- a/lib/guestfs.pod
+++ b/lib/guestfs.pod
@@ -1530,6 +1530,15 @@ Using:
 will force the direct and libvirt backends to use TCG (software
 emulation) instead of KVM (hardware accelerated virtualization).
 
+=head3 force_kvm
+
+Using:
+
+ export LIBGUESTFS_BACKEND_SETTINGS=force_kvm
+
+will force the direct and libvirt backends to use KVM (hardware
+accelerated virtualization) instead of TCG (software emulation).
+
 =head3 gdb
 
 The direct backend supports:
diff --git a/lib/launch-direct.c b/lib/launch-direct.c
index b6ed9766f..416a87fa0 100644
--- a/lib/launch-direct.c
+++ b/lib/launch-direct.c
@@ -385,6 +385,9 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   struct hv_param *hp;
   bool has_kvm;
   int force_tcg;
+  int force_kvm;
+  enum accel accel;
+  const char *accel_val;
   const char *cpu_model;
   CLEANUP_FREE char *append = NULL;
   CLEANUP_FREE_STRING_LIST char **argv = NULL;
@@ -434,8 +437,35 @@ 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;
+  }
+  else if (force_tcg) {
+    accel = FORCE_TCG;
+    accel_val = "tcg";
+  }
+  else if (force_kvm) {
+    accel = FORCE_KVM;
+    accel_val = "kvm"
+  }
+  else {
+    accel = BEST_ACCEL;
+    accel_val = "kvm:tcg";
+  }
+
+  if (!has_kvm) {
+    if (accel != FORCE_TCG)
+      debian_kvm_warning (g);
+    if (accel == 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.
@@ -527,13 +557,13 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
     append_list (MACHINE_TYPE);
 #endif
 #ifdef __aarch64__
-    if (has_kvm && !force_tcg)
+    if (has_kvm && accel != FORCE_TCG)
       append_list ("gic-version=host");
 #endif
-    append_list_format ("accel=%s", !force_tcg ? "kvm:tcg" : "tcg");
+    append_list_format ("accel=%s", accel_val);
   } end_list ();
 
-  cpu_model = guestfs_int_get_cpu_model (has_kvm && !force_tcg);
+  cpu_model = guestfs_int_get_cpu_model (has_kvm && accel != FORCE_TCG);
   if (cpu_model)
     arg ("-cpu", cpu_model);
 
@@ -690,7 +720,7 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
   }
 
   flags = 0;
-  if (!has_kvm || force_tcg)
+  if (!has_kvm || accel == FORCE_TCG)
     flags |= APPLIANCE_COMMAND_LINE_IS_TCG;
   append = guestfs_int_appliance_command_line (g, appliance, flags);
   arg ("-append", append);
diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c
index eff1c8f7e..b8ad8d265 100644
--- a/lib/launch-libvirt.c
+++ b/lib/launch-libvirt.c
@@ -772,6 +772,8 @@ parse_capabilities (guestfs_h *g, const char *capabilities_xml,
   xmlAttrPtr attr;
   size_t seen_qemu, seen_kvm;
   int force_tcg;
+  int force_kvm;
+  enum accel accel;
 
   doc = xmlReadMemory (capabilities_xml, strlen (capabilities_xml),
                        NULL, NULL, XML_PARSE_NONET);
@@ -819,11 +821,30 @@ parse_capabilities (guestfs_h *g, const char *capabilities_xml,
     }
   }
 
+  force_tcg = guestfs_int_get_backend_setting_bool (g, "force_tcg");
+  if (force_tcg == -1)
+    return -1;
+
+  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;
+  }
+  else if (force_tcg)
+    accel = FORCE_TCG;
+  else if (force_kvm)
+    accel = FORCE_KVM;
+  else
+    accel = BEST_ACCEL;
+
   /* 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 || accel == FORCE_KVM) && !seen_kvm) {
     CLEANUP_FREE char *backend = guestfs_get_backend (g);
 
     error (g,
@@ -841,11 +862,9 @@ parse_capabilities (guestfs_h *g, const char *capabilities_xml,
     return -1;
   }
 
-  force_tcg = guestfs_int_get_backend_setting_bool (g, "force_tcg");
-  if (force_tcg == -1)
-    return -1;
+  assert((accel != FORCE_KVM) || seen_kvm);
 
-  if (!force_tcg)
+  if (accel != FORCE_TCG)
     data->is_kvm = seen_kvm;
   else
     data->is_kvm = 0;
-- 
2.31.0.rc2.261.g7f71774620-goog