[libvirt] [PATCH] qemu: use default machine type if missing it in qemu command line

[Guannan Ren]

BZ:https://bugzilla.redhat.com/show_bug.cgi?id=871273
when using virsh qemu-attach to attach an existing qemu process,
if it misses the -M option in qemu command line, libvirtd crashed
because the NULL value of def->os.machine in later use.

Example:
/usr/libexec/qemu-kvm -name foo \
                      -cdrom /var/lib/libvirt/images/boot.img \
                      -monitor unix:/tmp/demo,server,nowait \

error: End of file while reading data: Input/output error
error: Failed to reconnect to the hypervisor

This patch tries to set default machine type if the value of
def->os.machine is still NULL after qemu command line parsing.
---
 src/qemu/qemu_command.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index fe99f5d..0b6d2f8 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -8768,6 +8768,17 @@ virDomainDefPtr qemuParseCommandLine(virCapsPtr caps,
         }
     }
 
+    if (!def->os.machine) {
+        const char *defaultMachine =
+                        virCapabilitiesDefaultGuestMachine(caps,
+                                                           def->os.type,
+                                                           def->os.arch,
+                                                           virDomainVirtTypeToString(def->virtType));
+        if (defaultMachine != NULL)
+            if (!(def->os.machine = strdup(defaultMachine)))
+                goto no_memory;
+    }
+
     if (!nographics && def->ngraphics == 0) {
         virDomainGraphicsDefPtr sdl;
         const char *display = qemuFindEnv(progenv, "DISPLAY");
-- 
1.7.1