Re: [PATCH v2 4/8] qemu-pr-helper: add PR_HELPER_CLEANUP for live migration

[Eric Blake <eblake@redhat.com>]

On Tue, Oct 13, 2026 at 02:17:48PM -0400, Stefan Hajnoczi wrote:
> Introduce a new vendor-specific SCSI command that acts similar to
> REGISTER AND IGNORE EXISTING KEY but also discards multipathd's state
> (including /etc/multipath/prkeys). This command will be used on the
> source after live migration completes successfully.
> 
> This cleanup step is necessary because multipathd will register the key
> it has stored when the path comes up again. This is undesirable when the
> guest has migrated to another host and can interfere with the migration
> process or the application running inside the guest.
> 
> Add a qemu-pr-manager protocol feature bit indicating that the new
> PR_HELPER_CLEANUP command is available. The command has no CDB fields
> other than OPCODE and the response contains no data aside from the usual
> result and sense data.
> 
> Note that the linker needs an explicit libmpathcmd dependency for
> mpath_disconnect() even though qemu-pr-helper.c already #included the
> mpath_cmd.h header before.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
> - Explicitly reject PR_HELPER_CLEAN commands in scsi_req_new() because
>   this is an internal command that guests cannot send
> - Add missing "forget" in comment (typo)
> ---
>  meson.build              |   2 +
>  include/scsi/constants.h |   1 +
>  scsi/pr-helper.h         |   3 +
>  hw/scsi/scsi-bus.c       |  10 +++
>  scsi/qemu-pr-helper.c    | 146 ++++++++++++++++++++++++++++++++++++---
>  5 files changed, 153 insertions(+), 9 deletions(-)
> 

> +++ b/scsi/qemu-pr-helper.c

> @@ -667,7 +786,8 @@ static int coroutine_fn prh_read_request(PRHelperClient *client,
>      }
>  
>      if (req->cdb[0] != PERSISTENT_RESERVE_OUT &&
> -        req->cdb[0] != PERSISTENT_RESERVE_IN) {
> +        req->cdb[0] != PERSISTENT_RESERVE_IN &&
> +        req->cdb[0] != PR_HELPER_CLEANUP) {
>          error_setg(errp, "Invalid CDB, closing socket.");

Worth removing the trailing . while you are in the neighborhood?

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org