Document background noise of RX packets from bridges (RHBZ#647987).

For more information see:
https://bugzilla.redhat.com/show_bug.cgi?id=647987#c9

3 files changed, 42 insertions, 0 deletions

diff --git a/virt-top/virt-top.1 b/virt-top/virt-top.1
index 1cd5843..2665e27 100755
--- a/virt-top/virt-top.1
+++ b/virt-top/virt-top.1
@@ -437,6 +437,20 @@ init file.
 Note that in the current implementation, options specified in
 the init file override options specified on the command line.
 This is a bug and this behaviour may change in the future.
+.SH "NOTES"
+.IX Header "NOTES"
+.SS "\s-1NETWORK\s0 \s-1RX\s0 \s-1BYTES\s0 \s-1AND\s0 \s-1PACKETS\s0"
+.IX Subsection "NETWORK RX BYTES AND PACKETS"
+Libvirt/virt\-top has no way to know that a packet transmitted to a
+guest was received (eg. if the guest is not listening).  In the
+network \s-1RX\s0 stats, virt-top reports the packets transmitted to the
+guest, on the basis that the guest might receive them.
+.PP
+In particular this includes broadcast packets.  Because of the way
+that Linux bridges work, if the guest is connected to a bridge, it
+will probably see a steady \*(L"background noise\*(R" of \s-1RX\s0 packets even when
+the network interface is idle or down.  These are caused by \s-1STP\s0
+packets generated by the bridge.
 .SH "SEE ALSO"
 .IX Header "SEE ALSO"
 \&\fItop\fR\|(1),
diff --git a/virt-top/virt-top.pod b/virt-top/virt-top.pod
index e11e814..4d7df4e 100755
--- a/virt-top/virt-top.pod
+++ b/virt-top/virt-top.pod
@@ -369,6 +369,21 @@ Note that in the current implementation, options specified in
 the init file override options specified on the command line.
 This is a bug and this behaviour may change in the future.
 
+=head1 NOTES
+
+=head2 NETWORK RX BYTES AND PACKETS
+
+Libvirt/virt-top has no way to know that a packet transmitted to a
+guest was received (eg. if the guest is not listening).  In the
+network RX stats, virt-top reports the packets transmitted to the
+guest, on the basis that the guest might receive them.
+
+In particular this includes broadcast packets.  Because of the way
+that Linux bridges work, if the guest is connected to a bridge, it
+will probably see a steady "background noise" of RX packets even when
+the network interface is idle or down.  These are caused by STP
+packets generated by the bridge.
+
 =head1 SEE ALSO
 
 L<top(1)>,
diff --git a/virt-top/virt-top.txt b/virt-top/virt-top.txt
index da737b8..de0681e 100644
--- a/virt-top/virt-top.txt
+++ b/virt-top/virt-top.txt
@@ -269,6 +269,19 @@ INIT FILE
     file override options specified on the command line. This is a bug and
     this behaviour may change in the future.
 
+NOTES
+  NETWORK RX BYTES AND PACKETS
+    Libvirt/virt-top has no way to know that a packet transmitted to a guest
+    was received (eg. if the guest is not listening). In the network RX
+    stats, virt-top reports the packets transmitted to the guest, on the
+    basis that the guest might receive them.
+
+    In particular this includes broadcast packets. Because of the way that
+    Linux bridges work, if the guest is connected to a bridge, it will
+    probably see a steady "background noise" of RX packets even when the
+    network interface is idle or down. These are caused by STP packets
+    generated by the bridge.
+
 SEE ALSO
     top(1), virsh(1), <http://www.libvirt.org/ocaml/>,
     <http://www.libvirt.org/>, <http://people.redhat.com/~rjones/>,