[PATCH v3 01/11] util: Introduce virHostGetDRMRenderNode helper

[Erik Skultety <eskultet@xxxxxxxxxx>]

This is the first step towards libvirt picking the first available
render node instead of QEMU. It also makes sense for us to be able to do
that, since we allow specifying the node directly for SPICE, so if
there's no render node specified by the user, we should pick the first
available one. The algorithm used for that is essentially the same as
the one QEMU uses.

Signed-off-by: Erik Skultety <eskultet@xxxxxxxxxx>
---
 src/libvirt_private.syms |  1 +
 src/util/virutil.c       | 53 ++++++++++++++++++++++++++++++++++++++++
 src/util/virutil.h       |  2 ++
 3 files changed, 56 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 5018a13e9c..c7f08f9620 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -3151,6 +3151,7 @@ virGetUserName;
 virGetUserRuntimeDirectory;
 virGetUserShell;
 virHexToBin;
+virHostGetDRMRenderNode;
 virHostHasIOMMU;
 virIndexToDiskName;
 virIsDevMapperDevice;
diff --git a/src/util/virutil.c b/src/util/virutil.c
index 974cffc2ee..da12a11e04 100644
--- a/src/util/virutil.c
+++ b/src/util/virutil.c
@@ -2145,3 +2145,56 @@ virHostHasIOMMU(void)
     VIR_DIR_CLOSE(iommuDir);
     return ret;
 }
+
+
+/**
+ * virHostGetDRMRenderNode:
+ *
+ * Picks the first DRM render node available. Missing DRI or missing DRM render
+ * nodes in the system results in an error.
+ *
+ * Returns an absolute path to the first render node available or NULL in case
+ * of an error with the error being reported.
+ * Caller is responsible for freeing the result string.
+ *
+ */
+char *
+virHostGetDRMRenderNode(void)
+{
+    char *ret = NULL;
+    DIR *driDir = NULL;
+    const char *driPath = "/dev/dri";
+    struct dirent *ent = NULL;
+    int dirErr = 0;
+    bool have_rendernode = false;
+
+    if (virDirOpen(&driDir, driPath) < 0)
+        return NULL;
+
+    while ((dirErr = virDirRead(driDir, &ent, driPath)) > 0) {
+        if (ent->d_type != DT_CHR)
+            continue;
+
+        if (STRPREFIX(ent->d_name, "renderD")) {
+            have_rendernode = true;
+            break;
+        }
+    }
+
+    if (dirErr < 0)
+        goto cleanup;
+
+    /* even if /dev/dri exists, there might be no renderDX nodes available */
+    if (!have_rendernode) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("No DRM render nodes available"));
+        goto cleanup;
+    }
+
+    if (virAsprintf(&ret, "%s/%s", driPath, ent->d_name) < 0)
+        goto cleanup;
+
+ cleanup:
+    VIR_DIR_CLOSE(driDir);
+    return ret;
+}
diff --git a/src/util/virutil.h b/src/util/virutil.h
index e0ab0da0f2..89bd21b148 100644
--- a/src/util/virutil.h
+++ b/src/util/virutil.h
@@ -222,6 +222,8 @@ unsigned long long virMemoryMaxValue(bool ulong) ATTRIBUTE_NOINLINE;
 
 bool virHostHasIOMMU(void);
 
+char *virHostGetDRMRenderNode(void);
+
 /**
  * VIR_ASSIGN_IS_OVERFLOW:
  * @rvalue: value that is checked (evaluated twice)
-- 
2.19.1

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