[Qemu-devel] [qemu devel] disable shared memory is not available with this QEMU binary

[Tony Krowiak <akrowiak@linux.vnet.ibm.com>]

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Commit 49d2e648e8087d154d8bf8b91f27c8e05e79d5a6 removed the QemuOptDesc 
elements from the
*desc* field of the *qemu_machine_opts *array defined in vl.c.  Since 
applying that patch to qemu
on my system, I can not start a guest from libvirt when certain machine 
options are configured
for the guest domain.  For example, if I configure the following for my 
guest domain:

     <memoryBacking>
         ...
         <nosharepages>
         ...
     </memoryBacking>

I get the following libvirt error when I try to start the guest:

     error: unsupported configuration: disable shared memory is not 
available with this QEMU binary

The *nosharepages *element generates the *-machine* option 
*mem-merge=off* on the QEMU command line.  The error is
thrown by libvirt because the QMP *query-command-line-options* command 
does not return *mem-merge* in the machine
options parameter list.  In fact, if I issue the 
*query-command-line-options* command via virsh as follows:

     virsh qemu-monitor-command guest_c2aa '{ "execute": 
"query-command-line-options", "arguments": { "option": "machine" } }'

No machine option parameters are returned:

{"return":[{"parameters":[],"option":"machine"}],"id":"libvirt-11"}


I took a look at the *qmp_query_command_line_options* function in 
*util/qemu-config.c*.  The function derives the
option parameters to return with the the query response from the 
QemuOptDesc elements contained in the
*desc* field of the *qemu_machine_opts *array defined in vl.c.  It 
appears that removing the
QemuOptDesc elements broke the *qmp_query_command_line_options* 
function.  If I restore the QemuOptDesc
elements removed by commit 49d2e648e8087d154d8bf8b91f27c8e05e79d5a6, I 
can start the guest with
*nosharepages* configured.

It would appear that a bug was introduced with commit 
49d2e648e8087d154d8bf8b91f27c8e05e79d5a6,
what say you?

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