(like reading or writing VM snapshots or disk image cluster tables). In this
case bottom halves are not marked as "replayable" and do not saved
into the log.
+
+Block devices
+-------------
+
+Block devices record/replay module intercepts calls of
+bdrv coroutine functions at the top of block drivers stack.
+To record and replay block operations the drive must be configured
+as following:
+ -drive file=disk.qcow,if=none,id=img-direct
+ -drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
+ -device ide-hd,drive=img-blkreplay
+
+blkreplay driver should be inserted between disk image and virtual driver
+controller. Therefore all disk requests may be recorded and replayed.
+
+All block completion operations are added to the queue in the coroutines.
+Queue is flushed at checkpoints and information about processed requests
+is recorded to the log. In replay phase the queue is matched with
+events read from the log. Therefore block devices requests are processed
+deterministically.
+
+Snapshotting
+------------
+
+New VM snapshots may be created in replay mode. They can be used later
+to recover the desired VM state. All VM states created in replay mode
+are associated with the moment of time in the replay scenario.
+After recovering the VM state replay will start from that position.
+
+Default starting snapshot name may be specified with icount field
+rrsnapshot as follows:
+ -icount shift=7,rr=record,rrfile=replay.bin,rrsnapshot=snapshot_name
+
+This snapshot is created at start of recording and restored at start
+of replaying. It also can be loaded while replaying to roll back
+the execution.
+
+Network devices
+---------------
+
+Record and replay for network interactions is performed with the network filter.
+Each backend must have its own instance of the replay filter as follows:
+ -netdev user,id=net1 -device rtl8139,netdev=net1
+ -object filter-replay,id=replay,netdev=net1
+
+Replay network filter is used to record and replay network packets. While
+recording the virtual machine this filter puts all packets coming from
+the outer world into the log. In replay mode packets from the log are
+injected into the network device. All interactions with network backend
+in replay mode are disabled.
+
+Audio devices
+-------------
+
+Audio data is recorded and replay automatically. The command line for recording
+and replaying must contain identical specifications of audio hardware, e.g.:
+ -soundhw ac97