Re: [Qemu-devel] [PATCH] hostmem: fix reference to uninit mr

[Paolo Bonzini]

On 10/03/2017 10:36, Peter Xu wrote:
> On Fri, Mar 10, 2017 at 10:17:30AM +0100, Peter Maydell wrote:
>> On 10 March 2017 at 09:59, Peter Xu <address@hidden> wrote:
>>> On Fri, Mar 10, 2017 at 09:33:57AM +0100, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 10/03/2017 05:13, Peter Xu wrote:
>>>>> Trying to get memory region size of an uninitialized memory region is
>>>>> probably not a good idea. Let's just do the alloc no matter what.
>>>>>
>>>>> Signed-off-by: Peter Xu <address@hidden>
>>>>
>>>> What is the effect of the bug? The idea was to do the initialization
>>>> once only (memory_region_size ought to be 0 when the MR is
>>>> uninitialized; now it is ugly but it made more sense when MemoryRegion
>>>> was just a C struct and not a QOM object).
>>>
>>> It's not really a bug. I just saw it, thought it was something not
>>> quite right, so posted a patch.
>>
>> We could reasonably abstract out the test into a function
>> bool backend_mr_initialized(HostMemoryBackend *backend)
>> {
>>     /* We forbid zero-length in file_backend_memory_alloc,
>>      * so zero always means "we haven't allocated the backend
>>      * MR yet".
>>      */
>>     return memory_region_size(&backend->mr) != 0;
>> }
>>
>> and use it in file_backend_memory_alloc(), set_mem_path()
>> and file_memory_backend_set_share(). That would make the intent
>> clearer here I think.
> 
> Agree, maybe use it in hostmem.c as well where capable?
> 
> (Paolo: I wasn't planning to add anything there, but if any of you
>  like me to do this cleanup, I would be glad to :)

Yes, please (to name things more consistently it should be
host_memory_backend_initialized).

Paolo