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Re: [Qemu-devel] Fwd: qemu drive mirror assert fault

From: Kevin Wolf
Subject: Re: [Qemu-devel] Fwd: qemu drive mirror assert fault
Date: Tue, 5 May 2015 13:48:25 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 05.05.2015 um 12:27 hat Fam Zheng geschrieben:
> On Tue, 05/05 12:13, Paolo Bonzini wrote:
> > 
> > 
> > On 05/05/2015 09:36, Fam Zheng wrote:
> > I don't think this commit is relevant.  The bug is caused by
> > bdrv_co_discard clearing the bitmap (which is not supported during
> > iteration, and is caught by the assertion).  That bdrv_reset_dirty is
> > not removed by the commit you pointed out.
> You are right, I think the bug is the bdrv_reset_dirty in bdrv_co_discard. The
> discard may zero out the src area (depending on the backend), we should
> probably replicate this to dest (actual data or the discard operation), rather
> than forgetting the change.

It depends. In its basic form, bdrv_discard() just means "I don't care
about the data any more". Then clearing the dirty bitmap is correct.

The content is only important if the caller used discard to write zeros
because can_write_zeroes_with_unmap = true. Do we have any such callers
apart from qemu-img convert?


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