Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Pull request

This pull request contains a virtio-blk/scsi performance optimization, event
loop scalability improvements, and a qtest-based device fuzzing framework.  I
am including the fuzzing patches because I have reviewed them and Thomas Huth
is currently away on leave.

# gpg: Signature made Sat 22 Feb 2020 08:50:05 GMT
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request: (31 commits)
  fuzz: add documentation to docs/devel/
  fuzz: add virtio-scsi fuzz target
  fuzz: add virtio-net fuzz target
  fuzz: add i440fx fuzz targets
  fuzz: add configure flag --enable-fuzzing
  fuzz: add target/fuzz makefile rules
  fuzz: add support for qos-assisted fuzz targets
  fuzz: support for fork-based fuzzing.
  main: keep rcu_atfork callback enabled for qtest
  exec: keep ram block across fork when using qtest
  fuzz: add fuzzer skeleton
  libqos: move useful qos-test funcs to qos_external
  libqos: split qos-test and libqos makefile vars
  libqos: rename i2c_send and i2c_recv
  qtest: add in-process incoming command handler
  libqtest: make bufwrite rely on the TransportOps
  libqtest: add a layer of abstraction to send/recv
  qtest: add qtest_server_send abstraction
  fuzz: add FUZZ_TARGET module type
  module: check module wasn't already initialized
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>