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docs: Expand the "BIOS bootloader" documentation for domainCaps 

Rewrite some parts for clarity, elaborate the meaning of some of the XML
attributes.  And where necessary, distinguish that we're dealing with
two different XML documents here:

  - the domainCapabilities XML, to detect the host "hypervisor"
    (QEMU/KVM) capabilities, and what libvirt knows about them.

  - the guest XML definition, i.e. what features a guest can use, based
    on the capabilities (of QEMU and libvirt and the host) reported in
    the domainCapabilities XML.

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Kashyap Chamarthy 2019-09-11 16:34:54 +02:00 committed by Michal Privoznik
parent 37942e8567
commit c5f690be75
1 changed files with 31 additions and 18 deletions
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49
docs/formatdomaincaps.html.in
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@ -143,38 +143,51 @@
&lt;domainCapabilities&gt;
</pre>
<p>The <code>firmware</code> enum corresponds to
<code>firmware</code> attribute of the <code>os</code> element.
Plain presence of this enum means that libvirt is capable of so
called firmware auto selection. The listed values then represent
accepted values for the domain attribute. Only values for which
there exists a firmware descriptor that matches machine type and
architecture are listed, i.e. those which won't cause a failure
on domain startup.
<p>The <code>firmware</code> enum corresponds to the
<code>firmware</code> attribute of the <code>os</code> element in
the domain XML. The presence of this enum means libvirt is capable
of the so-called firmware auto-selection feature. And the listed
firmware values represent the accepted input in the domain
XML. Note that the <code>firmware</code> enum reports only those
values for which a firmware "descriptor file" exists on the host.
Firmware descriptor file is a small JSON document that describes
details about a given BIOS or UEFI binary on the host, e.g. the
fimware binary path, its architecture, supported machine types,
NVRAM template, etc. This ensures that the reported values won't
cause a failure on guest boot.
</p>
<p>For the <code>loader</code> element, the following can occur:</p>
<dl>
<dt><code>value</code></dt>
<dd>List of known loader paths. Currently this is only used
to advertise known locations of OVMF binaries for qemu. Binaries
will only be listed if they actually exist on disk.</dd>
<dd>List of known firmware binary paths. Currently this is used
only to advertise the known location of OVMF binaries for
QEMU. OVMF binaries will only be listed if they actually exist on
host.</dd>
<dt><code>type</code></dt>
<dd>Whether loader is a typical BIOS (<code>rom</code>) or
an UEFI binary (<code>pflash</code>). This refers to
<code>type</code> attribute of the &lt;loader/&gt;
element.</dd>
<dd>Whether the boot loader is a typical BIOS (<code>rom</code>)
or a UEFI firmware (<code>pflash</code>). Each <code>value</code>
sub-element under the <code>type</code> enum represents a possible
value for the <code>type</code> attribute for the &lt;loader/&gt;
element in the domain XML. E.g. the presence
of <code>pfalsh</code> under the <code>type</code> enum means that
a domain XML can use UEFI firmware via: &lt;loader/&gt;
type="pflash" ...&gt;/path/to/the/firmware/binary/&lt;/loader&gt;.
</dd>
<dt><code>readonly</code></dt>
<dd>Options for the <code>readonly</code> attribute of the
&lt;loader/&gt; element.</dd>
&lt;loader/&gt; element in the domain XML.</dd>
<dt><code>secure</code></dt>
<dd>Options for the <code>secure</code> attribute of the
&lt;loader/&gt; element. Note, that <code>yes</code> is listed
only if there is a firmware that supports it.</dd>
&lt;loader/&gt; element in the domain XML. Note that the
value <code>yes</code> is listed only if libvirt detects a
firmware descriptor file that has path to an OVMF binary that
supports Secure boot, and lists its architecture and supported
machine type.</dd>
</dl>
<h3><a id="elementsCPU">CPU configuration</a></h3>