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

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] hostmem: fix reference to uninit mr
Date: Fri, 10 Mar 2017 11:06:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

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


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