Re: [Qemu-devel] [PATCH v2 0/4] monitor: do not rely on O_NONBLOCK for passed file descriptors

[mdroth <mdroth@linux.vnet.ibm.com>]

On Wed, Mar 27, 2013 at 09:17:30AM -0400, Luiz Capitulino wrote:
> On Wed, 27 Mar 2013 10:10:42 +0100
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> > There are several places where QEMU accidentally relies on the O_NONBLOCK state
> > of passed file descriptors.  Exposing O_NONBLOCK state makes it part of the QMP
> > API whenever getfd or fdset_add_fd are used!
> > 
> > Whether or not QEMU will use O_NONBLOCK is an implementation detail and should
> > be hidden from QMP clients.
> > 
> > This patch series addresses this in 3 steps:
> 
> Nice series:
> 
> Applied to the qmp branch, thanks.

Hi Luiz,

Eric/mjt have noted that this series fixes a number of issues in 1.4.0
and have requested it for 1.4.1

http://thread.gmane.org/gmane.comp.emulators.qemu/203851

The cut-off for 1.4.1 is Tuesday. Do you plan to send a pull for these soon?

> 
> > 
> > 1. Fix callers of monitor_handle_fd_param(), monitor_fdset_get_fd(), and
> >    monitor_get_fd() that depend on O_NONBLOCK being set.  Luckily there are
> >    only two instances and they are fixed in Patches 1 & 2.
> > 
> > 2. Rename socket_set_nonblock() to qemu_set_nonblock() just like
> >    qemu_set_cloexec().  This makes code cleaner when working with arbitrary
> >    file descriptors that may not be sockets.  See Patch 3.
> > 
> > 3. Clear O_NONBLOCK when a chardev receives file descriptors.  From now on QEMU
> >    can assume that passed file descriptors are in blocking mode.  Simply use
> >    qemu_set_nonblock(fd) if you want to enable O_NONBLOCK.  See Patch 4.
> > 
> > This fixes live migration with recent libvirt.  Libvirt checks if QEMU supports
> > file descriptor passing and, if yes, hands QEMU a socket with O_NONBLOCK set.
> > The migrate fd:<foo> code assumes the socket is in blocking mode.  The result
> > is a corrupted migration stream.  For more info on this bug, see:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=923124
> > 
> > Note that Michal Privoznik <mprivozn@redhat.com> also sent a libvirt patch so
> > that old QEMUs work with new libvirts:
> > 
> > https://www.redhat.com/archives/libvir-list/2013-March/msg01486.html
> > 
> > My patch series fixes the QMP API and allows old libvirts to work again with
> > new QEMUs.
> > 
> > v2:
> >  * Rename socket_set_nonblock() in Patch 1 to avoid code churn [eblake]
> >  * Avoid qemu_set_block(-1) calls that clobber errno [quintela]
> > 
> > Stefan Hajnoczi (4):
> >   oslib-posix: rename socket_set_nonblock() to qemu_set_nonblock()
> >   net: ensure "socket" backend uses non-blocking fds
> >   qemu-socket: set passed fd non-blocking in socket_connect()
> >   chardev: clear O_NONBLOCK on SCM_RIGHTS file descriptors
> > 
> >  block/nbd.c            |  2 +-
> >  block/sheepdog.c       |  2 +-
> >  include/qemu/sockets.h |  4 ++--
> >  migration.c            |  2 +-
> >  nbd.c                  |  8 ++++----
> >  net/socket.c           | 13 +++++++++----
> >  qemu-char.c            | 11 +++++++----
> >  savevm.c               |  2 +-
> >  slirp/misc.c           |  2 +-
> >  slirp/tcp_subr.c       |  4 ++--
> >  ui/vnc.c               |  2 +-
> >  util/oslib-posix.c     |  4 ++--
> >  util/oslib-win32.c     |  4 ++--
> >  util/qemu-sockets.c    |  5 +++--
> >  14 files changed, 37 insertions(+), 28 deletions(-)
> > 
> 
>