During vhost-user reconnect functionality we hit several issues, if
vhost-user-blk daemon is "crashed" or made disconnect during vhost
initialization. The general scenario is as follows:
  - vhost start routine is called
  - vhost write failed due to SIGPIPE
  - this call the disconnect routine and vhost_dev_cleanup routine
    which set to 0 all the field of the vhost_dev structure
  - return back to vhost start routine with the error
  - on the fail path vhost start routine tries to rollback the changes
    by using vhost_dev struct fields which were already reset
  - sometimes this leads to SIGSEGV, sometimes to SIGABRT
Before revising the vhost-user initialization code, we suggest adding
the sanity checks to be aware of the possible disconnect event and that
the vhost_dev structure can be in "uninitialized" state.

The vhost-user-blk daemon is updated with the additional
"--simulate-disconnect-stage=CASENUM" argument to simulate disconnect during
VHOST device initialization. For instance:
  1. $ ./vhost-user-blk -s ./vhost.sock -b test-img.raw --simulate-disconnect-stage=1
     This command will simulate disconnect in the SET_VRING_CALL handler.
     In this case the vhost device in QEMU is not set the started field to
     true.
  2. $ ./vhost-user-blk -s ./vhost.sock -b test-img.raw --simulate-disconnect-stage=2
     This command will simulate disconnect in the SET_VRING_NUM handler.
     In this case the started field is set to true.
These two cases test different QEMU parts. Also to trigger different code paths
disconnect should be simulated in two ways:
  - before any successful initialization
  - make successful initialization once and try to simulate disconnects
Also we catch SIGABRT on the migration start if vhost-user daemon disconnected
during vhost-user set log commands communication.

Dima Stepanov (7):
  contrib/vhost-user-blk: add option to simulate disconnect on init
  char-socket: return -1 in case of disconnect during tcp_chr_write
  char-socket: initialize reconnect timer only if close is emitted
  vhost: introduce wrappers to set guest notifiers for virtio device
  vhost-user-blk: add mechanism to track the guest notifiers init state
  vhost: check vring address before calling unmap
  vhost: add device started check in migration set log

 backends/cryptodev-vhost.c              |  26 +++++---
 backends/vhost-user.c                   |  16 ++---
 chardev/char-socket.c                   |  18 ++---
 contrib/libvhost-user/libvhost-user.c   |  30 +++++++++
 contrib/libvhost-user/libvhost-user.h   |  13 ++++
 contrib/vhost-user-blk/vhost-user-blk.c |  14 +++-
 hw/block/vhost-user-blk.c               |  23 +++----
 hw/net/vhost_net.c                      |  30 +++++----
 hw/scsi/vhost-scsi-common.c             |  15 ++---
 hw/virtio/vhost-user-fs.c               |  17 ++---
 hw/virtio/vhost-vsock.c                 |  18 +++--
 hw/virtio/vhost.c                       | 115 +++++++++++++++++++++++++++++---
 hw/virtio/virtio.c                      |  13 ++++
 include/hw/virtio/vhost.h               |   5 ++
 include/hw/virtio/virtio.h              |   1 +
 15 files changed, 256 insertions(+), 98 deletions(-)

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2.7.4