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

[Sam Eiderman]

Hi Richard,

I added both the v2 (slightly enhanced v1) and v3 (which uses the enum).

I have to say that I prefer v2 a lot more than v3 - the enum just
makes it worse in my opinion (maybe I just "implemented it wrong") -
tell me what you think.

Thanks!

On Tue, Mar 16, 2021 at 12:36 PM Sam Eiderman <sameid at google.com> wrote:
>
> 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
>