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[Qemu-devel] [PATCH v14 21/25] replay: document development rules
From: |
Pavel Dovgalyuk |
Subject: |
[Qemu-devel] [PATCH v14 21/25] replay: document development rules |
Date: |
Fri, 15 Mar 2019 15:10:18 +0300 |
User-agent: |
StGit/0.17.1-dirty |
This patch introduces docs/devel/replay.txt which describes the rules
that should be followed to make virtual devices usable in record/replay mode.
Signed-off-by: Pavel Dovgalyuk <address@hidden>
--
v9: fixed external virtual clock description (reported by Artem Pisarenko)
---
docs/devel/replay.txt | 46 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
create mode 100644 docs/devel/replay.txt
diff --git a/docs/devel/replay.txt b/docs/devel/replay.txt
new file mode 100644
index 0000000000..e641c35add
--- /dev/null
+++ b/docs/devel/replay.txt
@@ -0,0 +1,46 @@
+Record/replay mechanism, that could be enabled through icount mode, expects
+the virtual devices to satisfy the following requirements.
+
+The main idea behind this document is that everything that affects
+the guest state during execution in icount mode should be deterministic.
+
+Timers
+======
+
+All virtual devices should use virtual clock for timers that change the guest
+state. Virtual clock is deterministic, therefore such timers are deterministic
+too.
+
+Virtual devices can also use realtime clock for the events that do not change
+the guest state directly. When the clock ticking should depend on VM execution
+speed, use virtual clock with EXTERNAL attribute. It is not deterministic,
+but its speed depends on the guest execution. This clock is used by
+the virtual devices (e.g., slirp routing device) that lie outside the
+replayed guest.
+
+Bottom halves
+=============
+
+Bottom half callbacks, that affect the guest state, should be invoked through
+replay_bh_schedule_event or replay_bh_schedule_oneshot_event functions.
+Their invocations are saved in record mode and synchronized with the existing
+log in replay mode.
+
+Saving/restoring the VM state
+=============================
+
+All fields in the device state structure (including virtual timers)
+should be restored by loadvm to the same values they had before savevm.
+
+Avoid accessing other devices' state, because the order of saving/restoring
+is not defined. It means that you should not call functions like
+'update_irq' in post_load callback. Save everything explicitly to avoid
+the dependencies that may make restoring the VM state non-deterministic.
+
+Stopping the VM
+===============
+
+Stopping the guest should not interfere with its state (with the exception
+of the network connections, that could be broken by the remote timeouts).
+VM can be stopped at any moment of replay by the user. Restarting the VM
+after that stop should not break the replay by the unneeded guest state change.
- [Qemu-devel] [PATCH v14 00/25] Fixing record/replay and adding reverse debugging, Pavel Dovgalyuk, 2019/03/15
- Re: [Qemu-devel] [PATCH v14 00/25] Fixing record/replay and adding reverse debugging, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 22/25] util/qemu-timer: refactor deadline calculation for external timers, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 23/25] replay: fix replay shutdown, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 25/25] icount: clean up cpu_can_io before jumping to the next block, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 13/25] replay: implement replay-seek command, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 14/25] replay: refine replay-time module, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 06/25] replay: finish record/replay before closing the disks, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 21/25] replay: document development rules,
Pavel Dovgalyuk <=
- [Qemu-devel] [PATCH v14 10/25] qapi: introduce replay.json for record/replay-related stuff, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 09/25] replay: provide an accessor for rr filename, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 18/25] replay: describe reverse debugging in docs/replay.txt, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 15/25] replay: flush rr queue before loading the vmstate, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 04/25] replay: update docs for record/replay with block devices, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 11/25] replay: introduce info hmp/qmp command, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 19/25] replay: add BH oneshot event for block layer, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 01/25] replay: add missing fix for internal function, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 24/25] replay: rename step-related variables and functions, Pavel Dovgalyuk, 2019/03/15
- [Qemu-devel] [PATCH v14 03/25] replay: disable default snapshot for record/replay, Pavel Dovgalyuk, 2019/03/15