bandwidth: Adjust documentation

Recent autotest/virt-test testing on f20 discovered an anomaly in how
the bandwidth options are documented and used. This was discovered due
to a bug fix in the /sbin/tc utility found in iproute-3.11.0.1 (on f20)
in which overflow was actually caught and returned as an error. The fix
was first introduced in iproute-3.10 (search on iproute2 commit 'a303853e').

The autotest/virt-test test for virsh domiftune was attempting to send
the largest unsigned integer value (4294967295) for maximum value
testing. The libvirt xml implementation was designed to manage values
in kilobytes thus when this value was passed to /sbin/tc, it (now)
properly rejected the 4294967295kbps value.

Investigation of the problem discovered that formatdomain.html.in and
formatnetwork.html.in described the elements and property types slightly
differently, although they use the same code - virNetDevBandwidthParseRate()
(shared by portgroups, domains, and networks xml parsers). Rather than
have the descriptions in two places, this patch will combine and reword
the description under formatnetwork.html.in and have formatdomain.html.in
link to that description.

This documentation faux pas was continued into the virsh man page where
the bandwidth description for both 'attach-interface' and 'domiftune'
did not indicate the format of each value, thus leading to the test using
largest unsigned integer value assuming "bps" rather than "kbps", which
ultimately was wrong.

docs/formatdomain.html.in

@@ -3750,37 +3750,10 @@ qemu-kvm -net nic,model=? /dev/null
 
     <p>
       This part of interface XML provides setting quality of service. Incoming
-      and outgoing traffic can be shaped independently. The
+      and outgoing traffic can be shaped independently.
-      <code>bandwidth</code> element can have at most one <code>inbound</code>
+      The <code>bandwidth</code> element and its child elements are described
-      and at most one <code>outbound</code> child elements. Leaving any of these
+      in the <a href="formatnetwork.html#elementQoS">QoS</a> section of
-      children element out result in no QoS applied on that traffic direction.
+      the Network XML.
-      So, when you want to shape only domain's incoming traffic, use
-      <code>inbound</code> only, and vice versa. Each of these elements have one
-      mandatory attribute <code>average</code> (or <code>floor</code> as
-      described below). <code>average</code> specifies average bit rate on
-      the interface being shaped. Then there are two optional attributes:
-      <code>peak</code>, which specifies maximum rate at which interface can send
-      data, and <code>burst</code>, amount of bytes that can be burst at
-      <code>peak</code> speed. Accepted values for attributes are integer
-      numbers. The units for <code>average</code> and <code>peak</code> attributes
-      are kilobytes per second, and for the <code>burst</code> just kilobytes.
-      Note the limitation of implementation: the <code>peak</code> attribute in
-      <code>outbound</code> element is ignored (as linux ingress filters don't
-      know it yet). <span class="since">Since 0.9.4</span> The <code>inbound</code> can
-      optionally have <code>floor</code> attribute. This is there for
-      guaranteeing minimal throughput for shaped interfaces. This, however,
-      requires that all traffic goes through one point where QoS decisions can
-      take place. That's why this attribute works only for virtual networks for
-      now (that is <code>&lt;interface type='network'/&gt;</code> with a
-      forward type of route, nat, or no forward at all). Moreover, the
-      virtual network the interface is connected to is required to have at least
-      inbound QoS set (<code>average</code> at least). Moreover, with
-      <code>floor</code> attribute users don't need to specify
-      <code>average</code>. However, <code>peak</code> and <code>burst</code>
-      attributes still require <code>average</code>. Currently, linux kernel
-      doesn't allow ingress qdiscs to have any classes therefore
-      <code>floor</code> can be applied only on <code>inbound</code> and not
-      <code>outbound</code>. <span class="since">Since 1.0.1</span>
     </p>
 
     <h5><a name="elementVlanTag">Setting VLAN tag (on supported network types only)</a></h5>

docs/formatnetwork.html.in

@@ -412,49 +412,111 @@
 
       <p>
         The <code>&lt;bandwidth&gt;</code> element allows setting
-        quality of service for a particular network.
+        quality of service for a particular network
-        <span class="since">Since 0.9.4</span> The limits specified
+        (<span class="since">since 0.9.4</span>). Setting
-        are applied to the aggregate of all traffic to/from all guest
+        <code>bandwidth</code> for a network is supported only
-        interfaces attached to that network, <b>not</b> to each guest
+        for networks with a <code>&lt;forward&gt;</code> mode
-        interface individually.  Setting <code>bandwidth</code> for a
-        network is supported only for networks with
-        a <code>&lt;forward&gt;</code> mode
         of <code>route</code>, <code>nat</code>, or no mode at all
-        (i.e. an "isolated" network). <code>bandwidth</code> setting
+        (i.e. an "isolated" network). Setting <code>bandwidth</code>
         is <b>not</b> supported for forward modes
         of <code>bridge</code>, <code>passthrough</code>, <code>private</code>,
-        or <code>hostdev</code>, and attempts to do this will lead to
+        or <code>hostdev</code>. Attempts to do this will lead to
-        a failure to define the network (or to create a transient
+        a failure to define the network or to create a transient network.
-        network).
+      </p>
+      <p>
+        The <code>&lt;bandwidth&gt;</code> element can only be a
+        subelement of a domain's <code>&lt;interface&gt;</code>, a
+        subelement of a <code>&lt;network&gt;</code>, or a subelement of
+        a <code>&lt;portgroup&gt;</code> in a <code>&lt;network&gt;</code>.
+      </p>
+      <p>
+        As a subelement of a domain's <code>&lt;interface&gt;</code>,
+        the bandwidth only applies to that one interface of the domain.
+        As a subelement of a <code>&lt;network&gt;</code>, the bandwidth
+        is a total aggregate bandwidth to/from all guest interfaces attached
+        to that network, <b>not</b> to each guest interface individually.
+        If a domain's <code>&lt;interface&gt;</code> has
+        <code>&lt;bandwidth&gt;</code> element values higher
+        than the aggregate for the entire network, then the aggregate
+        bandwidth for the <code>&lt;network&gt;</code> takes precedence.
+        This is because the two choke points are independent of each other
+        where the domain's <code>&lt;interface&gt;</code> bandwidth control
+        is applied on the interface's tap device, while the
+        <code>&lt;network&gt;</code> bandwidth control is applied on the
+        interface part of the bridge device created for that network.
+      </p>
+      <p>
+        As a subelement of a
+        <code>&lt;portgroup&gt;</code> in a <code>&lt;network&gt;</code>,
+        if a domain's <code>&lt;interface&gt;</code> has a
+        <code>portgroup</code> attribute in its
+        <code>&lt;source&gt;</code> element <b>and</b> if the
+        <code>&lt;interface&gt;</code>
+        itself has no <code>&lt;bandwidth&gt;</code> element, then the
+        <code>&lt;bandwidth&gt;</code> element of the portgroup will be
+        applied individually to each guest interface defined to be a
+        member of that portgroup. Any <code>&lt;bandwidth&gt;</code>
+        element in the domain's <code>&lt;interface&gt;</code> definition
+        will override the setting in the portgroup
+        (<span class="since">since 1.0.1</span>).
       </p>
       <p>
         Incoming and outgoing traffic can be shaped independently. The
-        <code>bandwidth</code> element can have at most
+        <code>bandwidth</code> element can have at most one
-        one <code>inbound</code> and at most one <code>outbound</code>
+        <code>inbound</code> and at most one <code>outbound</code>
         child element. Leaving either of these children elements out
         results in no QoS applied for that traffic direction.  So,
-        when you want to shape only a network's incoming traffic, use
+        when you want to shape only incoming traffic, use
         <code>inbound</code> only, and vice versa. Each of these
-        elements have one mandatory attribute - <code>average</code>,
+        elements have one mandatory attribute - <code>average</code> (or
-        which specifies the desired average bit rate for the interface
+        <code>floor</code> as described below). The attributes are as follows,
-        being shaped (in kibibytes/second). There are also two
+        where accepted values for each attribute is an integer number.
-        optional attributes: <code>peak</code>, which specifies the
-        maximum rate at which the bridge can send data (again in
-        kibibytes/second), and <code>burst</code> - the amount of
-        bytes that can be transmitted in a single burst at
-        <code>peak</code> speed (in kibibytes). Accepted values for
-        attributes are integer numbers. The allotted bandwidth is
-        shared equally between domains connected to the network.
       </p>
+        <dl>
+          <dt><code>average</code></dt>
+          <dd>
+          Specifies the desired average bit rate for the interface
+          being shaped (in kilobytes/second).
+          </dd>
+          <dt><code>peak</code></dt>
+          <dd>
+          Optional attribute which specifies the maximum rate at
+          which the bridge can send data (in kilobytes/second).
+          Note the limitation of implementation: this attribute in the
+          <code>outbound</code> element is ignored (as Linux ingress
+          filters don't know it yet).
+          </dd>
+          <dt><code>burst</code></dt>
+          <dd>
+          Optional attribute which specifies the amount of kilobytes that
+          can be transmitted in a single burst at <code>peak</code> speed.
+          </dd>
+          <dt><code>floor</code></dt>
+          <dd>
+          Optional attribute available only for the <code>inbound</code>
+          element. This attribute guarantees minimal throughput for
+          shaped interfaces. This, however, requires that all traffic
+          goes through one point where QoS decisions can take place, hence
+          why this attribute works only for virtual networks for now
+          (that is <code>&lt;interface type='network'/&gt;</code> with a
+          forward type of route, nat, or no forward at all). Moreover, the
+          virtual network the interface is connected to is required to have
+          at least inbound QoS set (<code>average</code> at least). If
+          using the <code>floor</code> attribute users don't need to specify
+          <code>average</code>. However, <code>peak</code> and
+          <code>burst</code> attributes still require <code>average</code>.
+          Currently, the Linux kernel doesn't allow ingress qdiscs to have
+          any classes therefore <code>floor</code> can be applied only
+          on <code>inbound</code> and not <code>outbound</code>.
+          </dd>
+        </dl>
+
       <p>
-        A <code>&lt;portgroup&gt;</code> element can also include
+        Attributes <code>average</code>, <code>peak</code>, and
-        a <code>&lt;bandwidth&gt;</code> element. In that case, the
+        <code>burst</code> are available
-        specified bandwidth will be applied individually to each guest
+        <span class="since">since 0.9.4</span>, while the
-        interface defined to be a member of that portgroup.
+        <code>floor</code> attribute is available
-        Any <code>&lt;bandwidth&gt;</code> element in the guest's
+        <span class="since">since 1.0.1</span>.
-        interface definition will override the setting in the
-        portgroup.
-        <span class="since">Since 1.0.1</span>
       </p>
 
     <h5><a name="elementVlanTag">Setting VLAN tag (on supported network types only)</a></h5>
@@ -561,7 +623,7 @@
       network), and each portgroup has a name, as well as various
       subelements associated with it. The currently supported
       subelements are <code>&lt;bandwidth&gt;</code>
-      (documented <a href="formatdomain.html#elementQoS">here</a>)
+      (described <a href="formatnetwork.html#elementQoS">here</a>)
       and <code>&lt;virtualport&gt;</code>
       (documented <a href="formatdomain.html#elementsNICSDirect">here</a>).
       If a domain interface definition specifies a portgroup (by

tools/virsh.pod

@@ -681,7 +681,10 @@ or the MAC address.
 If no I<--inbound> or I<--outbound> is specified, this command will
 query and show the bandwidth settings. Otherwise, it will set the
 inbound or outbound bandwidth. I<average,peak,burst> is the same as
-in command I<attach-interface>.
+in command I<attach-interface>.  Values for I<average> and I<peak> are
+expressed in kilobytes per second, while I<burst> is expressed in kilobytes
+in a single burst at -I<peak> speed as described in the Network XML
+documentation at L<http://libvirt.org/formatnetwork.html#elementQoS>.
 
 If I<--live> is specified, affect a running guest.
 If I<--config> is specified, affect the next boot of a persistent guest.
@@ -2020,7 +2023,10 @@ of the network interface.  I<script> allows to specify a path to a script
 handling a bridge instead of the default one.  I<model> allows to specify the
 model type.  I<inbound> and I<outbound> control the bandwidth of the interface.
 I<peak> and I<burst> are optional, so "average,peak", "average,,burst" and
-"average" are also legal.
+"average" are also legal. Values for I<average> and I<peak> are
+expressed in kilobytes per second, while I<burst> is expressed in kilobytes
+in a single burst at -I<peak> speed as described in the Network XML
+documentation at L<http://libvirt.org/formatnetwork.html#elementQoS>.
 
 If I<--live> is specified, affect a running domain.
 If I<--config> is specified, affect the next startup of a persistent domain.