[PATCH 2/2] libxl: Fix up VRAM to minimum requirements

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

This is a bit debatable. On one side it hides configuration errors
in a way that makes them hard to spot. On the other side there is
at least one issue with (maybe some older versions) virt-manager.
Virt-manager sets VRAM directly, not using the default memory setting
but uses too small values for libxl. Worse, those versions do not seem
to allow to change VRAM from the GUI. So switching the video type to
VGA makes the guest fail to start until one manually adapts the VRAM
size in the XML definition.
With this change this would not happen but VRAM will be bigger than
the GUI says. This would not be that different from current Cirrus
behaviour. Only that in that case qemu seems to ignore the provided
size.

Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
---
 src/libxl/libxl_conf.c |   27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
index 2b5c469..9af8abe 100644
--- a/src/libxl/libxl_conf.c
+++ b/src/libxl/libxl_conf.c
@@ -1316,13 +1316,38 @@ libxlSetBuildGraphics(virDomainDefPtr def, libxl_domain_config *d_config)
      * type xen and vga is mapped to cirrus.
      */
     if (def->nvideos) {
+        unsigned int min_vram = 8 * 1024;
+
         switch (def->videos[0]->type) {
             case VIR_DOMAIN_VIDEO_TYPE_VGA:
             case VIR_DOMAIN_VIDEO_TYPE_XEN:
                 b_info->u.hvm.vga.kind = LIBXL_VGA_INTERFACE_TYPE_STD;
+                /*
+                 * Libxl enforces a minimal VRAM size of 8M when using
+                 * LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL or
+                 * 16M for LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN.
+                 * Avoid build failures and go with the minimum if less
+                 * is specified.
+                 */
+                switch (b_info->device_model_version) {
+                    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+                        min_vram = 8 * 1024;
+                        break;
+                    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+                    default:
+                        min_vram = 16 * 1024;
+                }
                 break;
             case VIR_DOMAIN_VIDEO_TYPE_CIRRUS:
                 b_info->u.hvm.vga.kind = LIBXL_VGA_INTERFACE_TYPE_CIRRUS;
+                switch (b_info->device_model_version) {
+                    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+                        min_vram = 4 * 1024; /* Actually the max, too */
+                        break;
+                    case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+                    default:
+                        min_vram = 8 * 1024;
+                }
                 break;
             default:
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
@@ -1330,7 +1355,7 @@ libxlSetBuildGraphics(virDomainDefPtr def, libxl_domain_config *d_config)
                                _("video type not supported by libxl"));
                 return -1;
         }
-        b_info->video_memkb = def->videos[0]->vram ?
+        b_info->video_memkb = (def->videos[0]->vram >= min_vram) ?
                               def->videos[0]->vram :
                               LIBXL_MEMKB_DEFAULT;
     } else {
-- 
1.7.9.5

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