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Re: [Qemu-devel] about correctness of IDE emulation

From: Fam Zheng
Subject: Re: [Qemu-devel] about correctness of IDE emulation
Date: Mon, 14 Mar 2016 09:42:48 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Sun, 03/13 14:37, Huaicheng Li (coperd) wrote:
> Hi all, 
> What I’m confused about is that:
> If one I/O is too large and may need several rounds (say 2) of DMA transfers,
> it seems the second round transfer begins only after the completion of the
> first part, by reading data from **IDEState**. But the IDEState info may have
> been changed by VCPU threads (by writing new I/Os to it) when the first
> transfer finishes. From the code, I see that IDE r/w call back function will
> continue the second transfer by referencing IDEState’s information. Wouldn’t
> this be problematic? Am I missing anything here?

Can you give an concrete example? I/O in VCPU threads that changes IDEState
must also take care of the DMA transfers, for example ide_reset() has
blk_aio_cancel and clears s->nsectors. If an I/O handler fails to do so, it is
a bug.


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