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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo