On Thu, Oct 05, 2023 at 01:08:52PM -0400, Stefan Hajnoczi wrote: > On Wed, Oct 04, 2023 at 02:58:57PM +0200, Hanna Czenczek wrote: > > There is no clearly defined purpose for the virtio status byte in > > vhost-user: For resetting, we already have RESET_DEVICE; and for virtio > > feature negotiation, we have [GS]ET_FEATURES. With the REPLY_ACK > > protocol extension, it is possible for SET_FEATURES to return errors > > (SET_PROTOCOL_FEATURES may be called before SET_FEATURES). > > > > As for implementations, SET_STATUS is not widely implemented. dpdk does > > implement it, but only uses it to signal feature negotiation failure. > > While it does log reset requests (SET_STATUS 0) as such, it effectively > > ignores them, in contrast to RESET_OWNER (which is deprecated, and today > > means the same thing as RESET_DEVICE). > > > > While qemu superficially has support for [GS]ET_STATUS, it does not > > forward the guest-set status byte, but instead just makes it up > > internally, and actually completely ignores what the back-end returns, > > only using it as the template for a subsequent SET_STATUS to add single > > bits to it. Notably, after setting FEATURES_OK, it never reads it back > > to see whether the flag is still set, which is the only way in which > > dpdk uses the status byte. > > > > As-is, no front-end or back-end can rely on the other side handling this > > field in a useful manner, and it also provides no practical use over > > other mechanisms the vhost-user protocol has, which are more clearly > > defined. Deprecate it. > > > > Suggested-by: Stefan Hajnoczi <stefa...@redhat.com> > > Signed-off-by: Hanna Czenczek <hre...@redhat.com> > > --- > > docs/interop/vhost-user.rst | 28 +++++++++++++++++++++------- > > 1 file changed, 21 insertions(+), 7 deletions(-) > > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
SET_STATUS is the only way to signal failure to acknowledge FEATURES_OK. The fact current backends never check errors does not mean they never will. So no, not applying this. -- MST