arm: qmp: add query-gic-capabilities interface

This patch add "query-gic-capabilities" but does not implement it. The
command is ARM-only. The command will return a list of GICCapability
structs that describes all GIC versions that current QEMU and system
support.

Libvirt is possibly the first consumer of this new command.

Before this patch, a libvirt user can successfully configure all kinds
of GIC devices for ARM guests, no matter whether current QEMU/kernel
supports them. If the specified GIC version/type is not supported, the
user will get an ambiguous "QEMU boot failure" error when trying to start
the VM. This is not user-friendly.

With this patch, libvirt should be able to query which type (and which
version) of GIC device is supported. Using this information, libvirt
can warn the user during configuration of guests when specified GIC
device type is not supported. Or better, we can just list those versions
that we support, and filter out the unsupported ones.

For example, if we got the query result:

{"return": [{"emulated": false, "version": 3, "kernel": true},
            {"emulated": true, "version": 2, "kernel": false}]}

then it means that we support emulated GIC version 2 using:

  qemu-system-aarch64 -M virt,accel=tcg,gic-version=2 ...

or KVM-accelerated GIC version 3 using:

  qemu-system-aarch64 -M virt,accel=kvm,gic-version=3 ...

If we specify other explicit GIC versions rather than the above, QEMU
will not be able to boot.

The community is working on a more generic way to query these kinds of
information about valid values of machine properties. However, due to
the importance of supporting this specific use case, weecided to first
implement this ad-hoc one; then when the generic method is ready, we
can move on to that one smoothly.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1458788142-17509-2-git-send-email-peterx@redhat.com
[PMM: tweaked commit message a bit; monitor.o is CONFIG_SOFTMMU only]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 29 insertions, 1 deletions

diff --git a/target-arm/Makefile.objs b/target-arm/Makefile.objs
index a80eb39..82cbe6b 100644
--- a/target-arm/Makefile.objs
+++ b/target-arm/Makefile.objs
@@ -1,5 +1,5 @@
 obj-y += arm-semi.o
-obj-$(CONFIG_SOFTMMU) += machine.o psci.o arch_dump.o
+obj-$(CONFIG_SOFTMMU) += machine.o psci.o arch_dump.o monitor.o
 obj-$(CONFIG_KVM) += kvm.o
 obj-$(call land,$(CONFIG_KVM),$(call lnot,$(TARGET_AARCH64))) += kvm32.o
 obj-$(call land,$(CONFIG_KVM),$(TARGET_AARCH64)) += kvm64.o
diff --git a/target-arm/monitor.c b/target-arm/monitor.c
new file mode 100644
index 0000000..4c9bef3
--- /dev/null
+++ b/target-arm/monitor.c
@@ -0,0 +1,28 @@
+/*
+ * QEMU monitor.c for ARM.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include "qemu/osdep.h"
+#include "qmp-commands.h"
+
+GICCapabilityList *qmp_query_gic_capabilities(Error **errp)
+{
+    return NULL;
+}