[PATCH 1/4] conf: add loader type 'none'

[Daniel Henrique Barboza <dbarboza@xxxxxxxxxxxxxxxx>]

Today, trying to boot a RISC-V Fedora Rawhide image in a RISC-V QEMU domain
results in the following error:

====
error: Failed to start domain 'riscv-fedora'
error: internal error: process exited while connecting to monitor:
2023-03-20T17:31:02.650862Z qemu-system-riscv64: Some ROM regions are overlapping
These ROM regions might have been loaded by direct user request or by default.
They could be BIOS/firmware images, a guest kernel, initrd or some other file loaded
into guest memory.
Check whether you intended to load all this guest code, and whether it has been built
to load to the correct addresses.
====

This happens because the default RISC-V QEMU firmware, OpenSBI, is
always loaded unless "-bios none" is passed in the command line, and the
Fedora Rawhide guest kernel has its own ROM. Other machines such as
PPC64 'pseries' shows the same behavior: the default firmware is always
loaded unless specified otherwise with the '-bios' option.

At this moment we don't have XML support for '-bios none'. Using
"<qemu:commandline>" works but it will leave the domain in a tainted
state. It'll also have unpredictable consequences with the autoselect
firmware feature libvirt has.

Add a new loader type 'none' that, if no path is specified and we're not
use firmware autoselection,  will tell QEMU that no default firmware
should be used:

<os>
  <loader type='none'/>
   (...)
</os>

Signed-off-by: Daniel Henrique Barboza <dbarboza@xxxxxxxxxxxxxxxx>
---
 src/conf/domain_conf.c            | 5 +++--
 src/conf/domain_validate.c        | 2 +-
 src/conf/schemas/domaincommon.rng | 1 +
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 9ef50c818b..d7a5cd094b 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -16837,7 +16837,7 @@ virDomainLoaderDefParseXMLLoader(virDomainLoaderDef *loader,
         return -1;
 
     if (virXMLPropEnum(loaderNode, "type", virDomainLoaderTypeFromString,
-                       VIR_XML_PROP_NONZERO, &loader->type) < 0)
+                       VIR_XML_PROP_NONE, &loader->type) < 0)
         return -1;
 
     if (!(loader->path = virXMLNodeContentString(loaderNode)))
@@ -26259,7 +26259,8 @@ virDomainLoaderDefFormat(virBuffer *buf,
         virBufferAsprintf(&loaderAttrBuf, " secure='%s'",
                           virTristateBoolTypeToString(loader->secure));
 
-    if (loader->type != VIR_DOMAIN_LOADER_TYPE_NONE)
+    if (loader->type != VIR_DOMAIN_LOADER_TYPE_NONE ||
+        (loader->type == VIR_DOMAIN_LOADER_TYPE_NONE && !loader->path))
         virBufferAsprintf(&loaderAttrBuf, " type='%s'",
                           virDomainLoaderTypeToString(loader->type));
 
diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c
index 5fb2d4971c..1fea9c8e6b 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -1664,7 +1664,7 @@ virDomainDefOSValidate(const virDomainDef *def,
         if (!loader)
             return 0;
 
-        if (!loader->path) {
+        if (loader->type != VIR_DOMAIN_LOADER_TYPE_NONE && !loader->path) {
             virReportError(VIR_ERR_XML_DETAIL, "%s",
                            _("no loader path specified and firmware auto selection disabled"));
             return -1;
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index 6158ed79ac..c96658e3a2 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -341,6 +341,7 @@
                   <choice>
                     <value>rom</value>
                     <value>pflash</value>
+                    <value>none</value>
                   </choice>
                 </attribute>
               </optional>
-- 
2.39.2