Re: [PATCH v5 4/5] Inter-VM shared memory PCI device

[Avi Kivity <avi@redhat.com>]

On 05/10/2010 08:25 PM, Anthony Liguori wrote:
> On 05/10/2010 11:59 AM, Avi Kivity wrote:
>> On 05/10/2010 06:38 PM, Anthony Liguori wrote:
>>>
>>>>> Otherwise, if the BAR is allocated during initialization, I would 
>>>>> have
>>>>> to use MAP_FIXED to mmap the memory.  This is what I did before the
>>>>> qemu_ram_mmap() function was added.
>>>>
>>>> What would happen to any data written to the BAR before the the 
>>>> handshake completed?  I think it would disappear.
>>>
>>> You don't have to do MAP_FIXED.  You can allocate a ram area and map 
>>> that in when disconnected.  When you connect, you create another ram 
>>> area and memcpy() the previous ram area to the new one.  You then 
>>> map the second ram area in.
>>
>> But it's a shared memory area.  Other peers could have connected and 
>> written some data in.  The memcpy() would destroy their data.
>
> Why try to attempt to support multi-master shared memory?  What's the 
> use-case?

(presuming you mean multiple writers?)

This is a surprising take.  What's the use of a single master shared 
memory area?

Most uses of shared memory among processes or threads are multi-master.  
One use case can be a shared cache among the various guests.

-- 
error compiling committee.c: too many arguments to function