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Re: [Qemu-devel] [PATCH v5 0/7] Deterministic replay extensions

From: Igor R
Subject: Re: [Qemu-devel] [PATCH v5 0/7] Deterministic replay extensions
Date: Tue, 15 Mar 2016 22:04:04 +0200

> This set of patches is related to the reverse execution and deterministic
> replay of qemu execution. It includes recording and replaying of serial 
> devices
> and block devices operations.
> With these patches one can record and deterministically replay behavior
> of the system with connected disk drives and serial communication ports
> (e.g., telnet terminal).
> Patches for deterministic replay of the block devices intercept 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

Thanks for the great feature.

A couple of questions:
* Is it possible to enable/disable recording when QEMU is already
running? I.e. is it ok to call replay_configure() or replay_enable()
from the monitor? Would it be possible to replay such a log?
* Currently, when running QEMU with the above drive configuration
(even w/o icount), savevm command doesn't seem to work correctly, and
subsequent loavm crashes QEMU. Is it just a bug or this feature
doesn't support snapshots?
* The replaying is much slower than the original scenario. Is it
affected by icount shift? What shift values would allow "real time"


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