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

[Stefan Hajnoczi]

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:

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 <address@hidden> 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.

Stefan Hajnoczi (4):
  net: ensure "socket" backend uses non-blocking fds
  qemu-socket: set passed fd non-blocking in socket_connect()
  oslib-posix: rename socket_set_nonblock() to qemu_set_nonblock()
  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           |  8 +++++---
 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, 33 insertions(+), 27 deletions(-)

-- 
1.8.1.4