virNetDevBandwidthSet() adds a queue discipline (qdisc) for each
interface that it will need to add tc transmit filters to, and the
filters are then attached to the qdisc.

There are other circumstances where some other function will need to
add tc transmit filters to an interface (in particular an upcoming
patch to the network driver nftables backend that will use a tc tx
filter to fix the checksum of dhcp packets), so that function will
also need a qdisc for the tx filter. To assure both always use exactly
the same qdisc, this patch puts the command that adds the tx filter
qdisc into a separate helper function that can (and will) be called
from either place

Signed-off-by: Laine Stump <laine@redhat.com>
---
 src/libvirt_private.syms      |  1 +
 src/util/virnetdevbandwidth.c | 30 +++++++++++++++++++++++++-----
 src/util/virnetdevbandwidth.h |  3 +++
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 5b9b44ef96..90a7c6fa01 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -2874,6 +2874,7 @@ virNetDevVFInterfaceStats;
 
 
 # util/virnetdevbandwidth.h
+virNetDevBandWidthAddTxFilterParentQdisc;
 virNetDevBandwidthClear;
 virNetDevBandwidthCopy;
 virNetDevBandwidthEqual;
diff --git a/src/util/virnetdevbandwidth.c b/src/util/virnetdevbandwidth.c
index 9c48844c5d..90eebe6576 100644
--- a/src/util/virnetdevbandwidth.c
+++ b/src/util/virnetdevbandwidth.c
@@ -266,11 +266,7 @@ virNetDevBandwidthSet(const char *ifname,
         if (tx->burst)
             burst = g_strdup_printf("%llukb", tx->burst);
 
-        cmd = virCommandNew(TC);
-        virCommandAddArgList(cmd, "qdisc", "add", "dev", ifname, "root",
-                             "handle", "1:", "htb", "default",
-                             hierarchical_class ? "2" : "1", NULL);
-        if (virCommandRun(cmd, NULL) < 0)
+        if (virNetDevBandWidthAddTxFilterParentQdisc(ifname, hierarchical_class) < 0)
             goto cleanup;
 
         /* If we are creating a hierarchical class, all non guaranteed traffic
@@ -794,3 +790,27 @@ virNetDevBandwidthSetRootQDisc(const char *ifname,
 
     return 0;
 }
+
+/**
+ * virNetDevBandwidthAddTxFilterParentQdisc:
+ * @ifname: name of interface that needs a qdisc to attach tx filters to
+ * @hierarchical_class: true if hierarchical classes will be used on this interface
+ *
+ * Add a root Qdisc (Queueing Discipline) for attaching Tx filters to
+ * @ifname.
+ *
+ * returns 0 on success, -1 on failure
+ */
+int
+virNetDevBandWidthAddTxFilterParentQdisc(const char *ifname,
+                                         bool hierarchical_class)
+{
+    g_autoptr(virCommand) cmd = NULL;
+
+    cmd = virCommandNew(TC);
+    virCommandAddArgList(cmd, "qdisc", "add", "dev", ifname, "root",
+                         "handle", "1:", "htb", "default",
+                         hierarchical_class ? "2" : "1", NULL);
+
+    return virCommandRun(cmd, NULL);
+}
diff --git a/src/util/virnetdevbandwidth.h b/src/util/virnetdevbandwidth.h
index 69c204389c..080d509d6e 100644
--- a/src/util/virnetdevbandwidth.h
+++ b/src/util/virnetdevbandwidth.h
@@ -84,3 +84,6 @@ int virNetDevBandwidthUpdateFilter(const char *ifname,
 int virNetDevBandwidthSetRootQDisc(const char *ifname,
                                    const char *qdisc)
     G_NO_INLINE;
+
+int virNetDevBandWidthAddTxFilterParentQdisc(const char *ifname,
+                                             bool hierarchical_class);
-- 
2.47.0