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

[Luiz Capitulino <lcapitulino@redhat.com>]

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.

> 
> 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(-)
>