[libvirt] [PATCH 02/12] qemu: command: spice: Pick the first available DRM render node

[Erik Skultety]

Up until now, we formatted 'rendernode=' onto QEMU cmdline only if the
user specified it in the XML, otherwise we let QEMU do it for us. This
causes permission issues because by default the /dev/dri/renderDX
permissions are as follows:

crw-rw----. 1 root video

There's literally no reason why it shouldn't be libvirt picking the DRM
render node instead of QEMU, that way (and because we're using
namespaces by default), we can safely relabel the device within the
namespace.

Signed-off-by: Erik Skultety <eskultet at redhat.com>
---
 src/qemu/qemu_command.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 23a6661c10..f6bee10d5c 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -8235,6 +8235,8 @@ qemuBuildGraphicsSPICECommandLine(virQEMUDriverConfigPtr cfg,
     }
 
     if (graphics->data.spice.gl == VIR_TRISTATE_BOOL_YES) {
+        char **rendernode = &graphics->data.spice.rendernode;
+
         if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_SPICE_GL)) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                            _("This QEMU doesn't support spice OpenGL"));
@@ -8246,17 +8248,20 @@ qemuBuildGraphicsSPICECommandLine(virQEMUDriverConfigPtr cfg,
         virBufferAsprintf(&opt, "gl=%s,",
                           virTristateSwitchTypeToString(graphics->data.spice.gl));
 
-        if (graphics->data.spice.rendernode) {
-            if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_SPICE_RENDERNODE)) {
-                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                               _("This QEMU doesn't support spice OpenGL rendernode"));
-                goto error;
-            }
-
-            virBufferAddLit(&opt, "rendernode=");
-            virQEMUBuildBufferEscapeComma(&opt, graphics->data.spice.rendernode);
-            virBufferAddLit(&opt, ",");
+        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_SPICE_RENDERNODE)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("This QEMU doesn't support spice OpenGL rendernode"));
+            goto error;
         }
+
+        /* pick the first DRM render node if none was specified */
+        if (!*rendernode &&
+            !(*rendernode = virHostGetDRMRenderNode()))
+            goto error;
+
+        virBufferAddLit(&opt, "rendernode=");
+        virQEMUBuildBufferEscapeComma(&opt, graphics->data.spice.rendernode);
+        virBufferAddLit(&opt, ",");
     }
 
     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_SEAMLESS_MIGRATION)) {
-- 
2.19.1