On Mon, 2019-09-09 at 11:45 -0400, Michael S. Tsirkin wrote: > On Mon, Sep 09, 2019 at 05:34:13PM +0200, Johannes Berg wrote: > > On Mon, 2019-09-09 at 17:26 +0200, Johannes Berg wrote: > > > Maybe instead we should just add a "VHOST_USER_REPLY_ERROR" bit (e.g. > > > bit 4 after NEED_REPLY). Qemu in vhost_user_read_header() validates that > > > it received REPLY_MASK | VERSION, so it would reject the message at that > > > point. > > > > > > Another possibility would be to define the highest bit of the 'request' > > > field to indicate an error, so for GET_FEATURES we'd return the value > > > 0x80000000 | GET_FEATURES. > > > > However, one way or another, that basically leaves us with three > > different ways of indicating an error: > > > > 1) already defined errors in existing messages - we can't change them > > since those are handled at runtime now, e.g. VHOST_USER_POSTCOPY_END > > returns a u64 value with an error status, and current code cannot > > deal with an error flag in the 'request' or 'flags' field > > 2) F_REPLY_ACK errors to messages that do not specify a response at all > > 3) this new way of indicating an error back from messages that specify > > a response, but the response has no inherent way of returning an > > error > > > > To me that really feels a bit too complex from the spec POV. But I don't > > see a way to generalize this without another extension, and again the > > device cannot choose which extensions it supports since the master > > chooses them and just sets them. > > > > Perhaps I really should just stick a "g_assert()" into the code at that > > point, > > There's the old way: close the socket. > This will make reads fail gracefully. > If we don't want complexity right now, I'd go with that.
D'oh, good point. OK, I'll do that. Though it's almost equivalent in libvhost-user to just asserting, since it's mostly set up to just handle a single connection and then quit. Alright, thanks. Like I said, I'll send some more patches all around once I get it working, right now I'm crashing in some weird ways that I need to debug :) johannes
