On Tue, 08/22 15:18, Paolo Bonzini wrote: > diff --git a/docs/pr-manager.rst b/docs/pr-manager.rst
Is docs/interop/persistent-reservation-manager.rst better? (Move to interop/ and de-abbreviate) ... > new file mode 100644 > index 0000000000..b6089fb57c > --- /dev/null > +++ b/docs/pr-manager.rst > @@ -0,0 +1,51 @@ > +====================================== > +Persistent reservation managers > +====================================== > + > +SCSI persistent Reservations allow restricting access to block devices > +to specific initiators in a shared storage setup. When implementing > +clustering of virtual machines, it is a common requirement for virtual > +machines to send persistent reservation SCSI commands. However, > +the operating system restricts sending these commands to unprivileged > +programs because incorrect usage can disrupt regular operation of the > +storage fabric. > + > +For this reason, QEMU's SCSI passthrough devices, ``scsi-block`` > +and ``scsi-generic`` (both are only available on Linux) can delegate > +implementation of persistent reservations to a separate object, > +the "persistent reservation manager". Only PERSISTENT RESERVE OUT and > +PERSISTENT RESERVE IN commands are passed to the persistent reservation > +manager object; other commands are processed by QEMU as usual. > + > +----------------------------------------- > +Defining a persistent reservation manager > +----------------------------------------- > + > +A persistent reservation manager is an instance of a subclass of the > +"pr-manager" QOM class. Or is this abstraction class the reason it is not under interop? Why not just define the protocol? > + > +Right now only one subclass is defined, ``pr-manager-helper``, which > +forwards the commands to an external privileged helper program > +over Unix sockets. The helper program only allows sending persistent > +reservation commands to devices for which QEMU has a file descriptor, > +so that QEMU will not be able to effect persistent reservations > +unless it has access to both the socket and the device. > + > +``pr-manager-helper`` has a single string property, ``path``, which > +accepts the path to the helper program's Unix socket. For example, > +the following command line defines a ``pr-manager-helper`` object and > +attaches it to a SCSI passthrough device:: > + > + $ qemu-system-x86_64 > + -device virtio-scsi \ > + -object > pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock > + -drive > if=none,id=hd,driver=raw,file.filename=/dev/sdb,file.pr-manager=helper0 > + -device scsi-block,drive=hd > + > +Alternatively, using ``-blockdev``:: > + > + $ qemu-system-x86_64 > + -device virtio-scsi \ > + -object > pr-manager-helper,id=helper0,path=/var/run/qemu-pr-helper.sock > + -blockdev > node-name=hd,driver=raw,file.driver=host_device,file.filename=/dev/sdb,file.pr-manager=helper0 > + -device scsi-block,drive=hd Fam
