Re: Get a vm fd using kvm API's ioctls

[Vincent KHERBACHE <vincent.kherbache@inria.fr>]

Le 05/02/2014 17:52, Paolo Bonzini a écrit :
> Il 05/02/2014 17:30, Vincent KHERBACHE ha scritto:
>> Hi all,
>>
>> I'm trying to get the dirty bitmap of a specific VM, using
>> KVM_GET_DIRTY_LOG ioctl.
>>
>> For this purpose, I should be able to get the file descriptor of an
>> existing VM by doing something like :
>>
>> kvm_fd = open("/dev/kvm")
>> ...
>> b = ioctl(KVM_GET_DIRTY_LOG, vm_fd)
>>
>>
>> I also can see, from the API documentation
>> (https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt), that
>> there is the following restriction concerning VM ioctls :
>>
>> "Only run VM ioctls from the same process (address space) that was used
>> to create the VM."
>>
>>
>> Is there a way to get the fd of a running VM (created from an other
>> process), or maybe a better/easier manner to get the dirty bitmap ?
> 
> You can get ask the other process to retrieve the dirty bitmap and place
> it in a shared memory segment.
> 
> However, note that KVM_GET_DIRTY_LOG retrieves _and clears_ the dirty
> bitmap.  So if the "owner" of the running VM is already using the dirty
> bitmap, calling KVM_GET_DIRTY_LOG will likely break that usage.


Thank you for your reply !

I take note of your remark about the bitmap clearing, it could be an
effective issue.

But I really have no idea of how can I 'ask' something the other process ?


Regards.
-- 
Vincent KHERBACHE