On 08/22/2017 08:18 AM, Paolo Bonzini wrote:
> Introduce a privileged helper to run persistent reservation commands.
> This lets virtual machines send persistent reservations without using
> CAP_SYS_RAWIO or out-of-tree patches.  The helper uses Unix permissions
> and SCM_RIGHTS to restrict access to processes that can access its socket
> and prove that they have an open file descriptor for a raw SCSI device.
> 
> The next patch will also correct the usage of persistent reservations
> with multipath devices.
> 
> It would also be possible to support for Linux's IOC_PR_* ioctls in
> the future, to support NVMe devices.  For now, however, only SCSI is
> supported.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

> +++ b/docs/interop/pr-helper.rst
> @@ -0,0 +1,78 @@
> +..
> +
> +======================================
> +Persistent reservation helper protocol
> +======================================
> +
> +QEMU's SCSI passthrough devices, ``scsi-block`` and ``scsi-generic``,
> +can delegate implementation of persistent reservations to an external
> +(and typically privilege) program.  Persistent Reservations allow

s/privilege/privileged/


> +
> +If a bit is 1 in ``requested_features`` and 0 in ``supported_features``,
> +the corresponding feature is not supported by the helper and the connection
> +is closed.  On the other hand, it is acceptable for a bit to be 0 in
> +``requested_features`` and 1 in ``supported_features``; in this case,
> +he helper will not enable the feature.

s/^he/the/

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org