replay: update documentation
This patch clarifies the description of the record/replay feature in docs/replay.txt Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru> Message-Id: <20180227095333.1060.1331.stgit@pasha-VirtualBox> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
This commit is contained in:
Pavel Dovgalyuk
Paolo Bonzini
parent
0b30dc0164
commit
7273db9d28
@ -7,14 +7,10 @@ See the COPYING file in the top-level directory.
|
||||
Record/replay
|
||||
-------------
|
||||
|
||||
Record/replay functions are used for the reverse execution and deterministic
|
||||
replay of qemu execution. This implementation of deterministic replay can
|
||||
be used for deterministic debugging of guest code through a gdb remote
|
||||
interface.
|
||||
|
||||
Record/replay functions are used for the deterministic replay of qemu execution.
|
||||
Execution recording writes a non-deterministic events log, which can be later
|
||||
used for replaying the execution anywhere and for unlimited number of times.
|
||||
It also supports checkpointing for faster rewinding during reverse debugging.
|
||||
It also supports checkpointing for faster rewind to the specific replay moment.
|
||||
Execution replaying reads the log and replays all non-deterministic events
|
||||
including external input, hardware clocks, and interrupts.
|
||||
|
||||
@ -28,16 +24,36 @@ Deterministic replay has the following features:
|
||||
input devices.
|
||||
|
||||
Usage of the record/replay:
|
||||
* First, record the execution, by adding the following arguments to the command line:
|
||||
'-icount shift=7,rr=record,rrfile=replay.bin -net none'.
|
||||
Block devices' images are not actually changed in the recording mode,
|
||||
* First, record the execution with the following command line:
|
||||
qemu-system-i386 \
|
||||
-icount shift=7,rr=record,rrfile=replay.bin \
|
||||
-drive file=disk.qcow2,if=none,id=img-direct \
|
||||
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay \
|
||||
-device ide-hd,drive=img-blkreplay \
|
||||
-netdev user,id=net1 -device rtl8139,netdev=net1 \
|
||||
-object filter-replay,id=replay,netdev=net1
|
||||
* After recording, you can replay it by using another command line:
|
||||
qemu-system-i386 \
|
||||
-icount shift=7,rr=replay,rrfile=replay.bin \
|
||||
-drive file=disk.qcow2,if=none,id=img-direct \
|
||||
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay \
|
||||
-device ide-hd,drive=img-blkreplay \
|
||||
-netdev user,id=net1 -device rtl8139,netdev=net1 \
|
||||
-object filter-replay,id=replay,netdev=net1
|
||||
The only difference with recording is changing the rr option
|
||||
from record to replay.
|
||||
* Block device images are not actually changed in the recording mode,
|
||||
because all of the changes are written to the temporary overlay file.
|
||||
* Then you can replay it by using another command
|
||||
line option: '-icount shift=7,rr=replay,rrfile=replay.bin -net none'
|
||||
* '-net none' option should also be specified if network replay patches
|
||||
are not applied.
|
||||
This behavior is enabled by using blkreplay driver. It should be used
|
||||
for every enabled block device, as described in 'Block devices' section.
|
||||
* '-net none' option should be specified when network is not used,
|
||||
because QEMU adds network card by default. When network is needed,
|
||||
it should be configured explicitly with replay filter, as described
|
||||
in 'Network devices' section.
|
||||
* Interaction with audio devices and serial ports are recorded and replayed
|
||||
automatically when such devices are enabled.
|
||||
|
||||
Papers with description of deterministic replay implementation:
|
||||
Academic papers with description of deterministic replay implementation:
|
||||
http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.html
|
||||
http://dl.acm.org/citation.cfm?id=2786805.2803179
|
||||
|
||||
@ -46,8 +62,11 @@ Modifications of qemu include:
|
||||
* saving different asynchronous events (e.g. system shutdown) into the log
|
||||
* synchronization of the bottom halves execution
|
||||
* synchronization of the threads from thread pool
|
||||
* recording/replaying user input (mouse and keyboard)
|
||||
* recording/replaying user input (mouse, keyboard, and microphone)
|
||||
* adding internal checkpoints for cpu and io synchronization
|
||||
* network filter for recording and replaying the packets
|
||||
* block driver for making block layer deterministic
|
||||
* serial port input record and replay
|
||||
|
||||
Locking and thread synchronisation
|
||||
----------------------------------
|
||||
@ -77,12 +96,11 @@ Non-deterministic events
|
||||
Our record/replay system is based on saving and replaying non-deterministic
|
||||
events (e.g. keyboard input) and simulating deterministic ones (e.g. reading
|
||||
from HDD or memory of the VM). Saving only non-deterministic events makes
|
||||
log file smaller, simulation faster, and allows using reverse debugging even
|
||||
for realtime applications.
|
||||
log file smaller and simulation faster.
|
||||
|
||||
The following non-deterministic data from peripheral devices is saved into
|
||||
the log: mouse and keyboard input, network packets, audio controller input,
|
||||
USB packets, serial port input, and hardware clocks (they are non-deterministic
|
||||
serial port input, and hardware clocks (they are non-deterministic
|
||||
too, because their values are taken from the host machine). Inputs from
|
||||
simulated hardware, memory of VM, software interrupts, and execution of
|
||||
instructions are not saved into the log, because they are deterministic and
|
||||
@ -205,7 +223,7 @@ 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 file=disk.qcow2,if=none,id=img-direct
|
||||
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
|
||||
-device ide-hd,drive=img-blkreplay
|
||||
|
||||
@ -234,6 +252,12 @@ 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.
|
||||
|
||||
Use QEMU monitor to create additional snapshots. 'savevm <name>' command
|
||||
created the snapshot and 'loadvm <name>' restores it. To prevent corruption
|
||||
of the original disk image, use overlay files linked to the original images.
|
||||
Therefore all new snapshots (including the starting one) will be saved in
|
||||
overlays and the original image remains unchanged.
|
||||
|
||||
Network devices
|
||||
---------------
|
||||
|
||||
@ -255,6 +279,14 @@ 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
|
||||
|
||||
Serial ports
|
||||
------------
|
||||
|
||||
Serial ports input is recorded and replay automatically. The command lines
|
||||
for recording and replaying must contain identical number of ports in record
|
||||
and replay modes, but their backends may differ.
|
||||
E.g., '-serial stdio' in record mode, and '-serial null' in replay mode.
|
||||
|
||||
Replay log format
|
||||
-----------------
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user