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>
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