On Thu, Apr 07, 2022 at 03:36:54PM +0200, Kevin Wolf wrote:
> While implementing a vhost-user-blk driver for libblkio, I found some
> problems with VHOST_USER_ADD/REM_MEM_REG both in the spec and in the
> implementations in QEMU and libvhost-user that this series addresses.
>
> I also noticed that you can use REM_MEM_REG or SET_MEM_TABLE to unmap a
> memory region that is still in use (e.g. a block I/O request using
> addresses from the region has been started, but not completed yet),
> which is not great. I'm not sure how to fix this best, though.
>
> We would have to wait for these requests to complete (maybe introduce a
> refcount and wait for it to drop to zero), but waiting seems impossible
> in libvhost-user because it doesn't have any main loop integration. Just
> failing the memory region removal would be safe, but potentially a
> rather awkward interface because clients would have to implement some
> retry logic.
>
> Kevin Wolf (3):
> docs/vhost-user: Clarifications for VHOST_USER_ADD/REM_MEM_REG
> libvhost-user: Fix extra vu_add/rem_mem_reg reply
> vhost-user: Don't pass file descriptor for VHOST_USER_REM_MEM_REG
>
> docs/interop/vhost-user.rst | 17 +++++++++++++++++
> hw/virtio/vhost-user.c | 2 +-
> subprojects/libvhost-user/libvhost-user.c | 17 +++++++----------
> 3 files changed, 25 insertions(+), 11 deletions(-)
>
> --
> 2.35.1
>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>