Thank you for reminding me of this socket short read issue! It seems we still need customized vu_message_read because libvhost-user assumes we will always get a full-size VhostUserMsg and hasn't taken care of this short read case. I will improve libvhost-user's vu_message_read by making it keep reading from socket util getting enough bytes. I assume short read is a rare case thus introduced performance penalty would be negligible.
On Thu, Feb 27, 2020 at 3:41 PM Stefan Hajnoczi <stefa...@redhat.com> wrote: > > On Wed, Feb 26, 2020 at 11:18:41PM +0800, Coiby Xu wrote: > > Hi Stefan, > > > > Thank you for reviewing my code! > > > > I tried to reach you on IRC. But somehow either you missed my message > > or I missed your reply. So I will reply by email instead. > > > > If we use qio_channel_set_aio_fd_handler to monitor G_IO_IN event, > > i.e. use vu_dispatch as the read handler, then we can re-use > > vu_message_read. And "removing the blocking recv from libvhost-user" > > isn't necessary because "the operation of poll() and ppoll() is not > > affected by the O_NONBLOCK flag" despite that we use > > qio_channel_set_blocking before calling qio_channel_set_aio_fd_handler > > to make recv non-blocking. > > I'm not sure I understand. poll() just says whether the file descriptor > is readable. It does not say whether enough bytes are readable :). So > our callback will be invoked if there is 1 byte ready, but when we try > to read 20 bytes either it will block (without O_NONBLOCK) or return > only 1 byte (with O_NONBLOCK). Neither case is okay, so I expect that > code changes will be necessary. > > But please go ahead and send the next revision and I'll take a look. > > Stefan -- Best regards, Coiby
