Back in the day when I was implementing QoS for networks there
were no self inflating virBitmaps. Only the static ones.
Therefore, I had to allocate the whole 8KB of memory in order to
keep track of used/unused class IDs. This is rather wasteful
because nobody is ever gonna use that much classes (kernel
overhead would drastically lower the bandwidth). Anyway, now that
we have self inflating bitmaps we can start small and allocate
more if there's need for it.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 src/conf/virnetworkobj.c    | 18 ++++++++++--------
 src/network/bridge_driver.c |  5 +++--
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/src/conf/virnetworkobj.c b/src/conf/virnetworkobj.c
index 918ef44ea..455b604bb 100644
--- a/src/conf/virnetworkobj.c
+++ b/src/conf/virnetworkobj.c
@@ -34,8 +34,10 @@
 
 VIR_LOG_INIT("conf.virnetworkobj");
 
-/* currently, /sbin/tc implementation allows up to 16 bits for minor class size */
-#define CLASS_ID_BITMAP_SIZE (1<<16)
+/* Currently, /sbin/tc implementation allows up to 16 bits for
+ * minor class size. But the initial bitmap doesn't have to be
+ * that big. */
+#define INIT_CLASS_ID_BITMAP_SIZE (1<<4)
 
 struct _virNetworkObj {
     virObjectLockable parent;
@@ -100,13 +102,14 @@ virNetworkObjNew(void)
     if (!(obj = virObjectLockableNew(virNetworkObjClass)))
         return NULL;
 
-    if (!(obj->classIdMap = virBitmapNew(CLASS_ID_BITMAP_SIZE)))
+    if (!(obj->classIdMap = virBitmapNew(INIT_CLASS_ID_BITMAP_SIZE)))
         goto error;
 
     /* The first three class IDs are already taken */
-    ignore_value(virBitmapSetBit(obj->classIdMap, 0));
-    ignore_value(virBitmapSetBit(obj->classIdMap, 1));
-    ignore_value(virBitmapSetBit(obj->classIdMap, 2));
+    if (virBitmapSetBitExpand(obj->classIdMap, 0) < 0 ||
+        virBitmapSetBitExpand(obj->classIdMap, 1) < 0 ||
+        virBitmapSetBitExpand(obj->classIdMap, 2) < 0)
+        goto error;
 
     virObjectLock(obj);
 
@@ -909,8 +912,7 @@ virNetworkLoadState(virNetworkObjListPtr nets,
         ctxt->node = node;
         if ((classIdStr = virXPathString("string(./class_id[1]/@bitmap)",
                                          ctxt))) {
-            if (virBitmapParse(classIdStr, &classIdMap,
-                               CLASS_ID_BITMAP_SIZE) < 0) {
+            if (!(classIdMap = virBitmapParseUnlimited(classIdStr))) {
                 VIR_FREE(classIdStr);
                 goto error;
             }
diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 74ce92e43..e8d093a31 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -5395,9 +5395,10 @@ networkNextClassID(virNetworkObjPtr obj)
     ssize_t ret = 0;
     virBitmapPtr classIdMap = virNetworkObjGetClassIdMap(obj);
 
-    ret = virBitmapNextClearBit(classIdMap, -1);
+    if ((ret = virBitmapNextClearBit(classIdMap, -1)) < 0)
+        ret = virBitmapSize(classIdMap);
 
-    if (ret < 0 || virBitmapSetBit(classIdMap, ret) < 0)
+    if (virBitmapSetBitExpand(classIdMap, ret) < 0)
         return -1;
 
     return ret;
-- 
2.13.0

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On 08/17/2017 03:32 AM, Michal Privoznik wrote:
> Back in the day when I was implementing QoS for networks there
> were no self inflating virBitmaps. Only the static ones.
> Therefore, I had to allocate the whole 8KB of memory in order to
> keep track of used/unused class IDs. This is rather wasteful
> because nobody is ever gonna use that much classes (kernel
> overhead would drastically lower the bandwidth). Anyway, now that
> we have self inflating bitmaps we can start small and allocate
> more if there's need for it.
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  src/conf/virnetworkobj.c    | 18 ++++++++++--------
>  src/network/bridge_driver.c |  5 +++--
>  2 files changed, 13 insertions(+), 10 deletions(-)
> 

Reviewed-by: John Ferlan <jferlan@redhat.com>

John

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