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

[liu ping fan]

On Wed, Mar 27, 2013 at 12:07 AM, Stefan Hajnoczi <address@hidden> 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

If in future, we push more backend on their dedicated thread, will the
related fd be block?
> 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
>
>