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From: Lutz Vieweg <lvml@5t9.de>
Date: Fri, 22 Apr 2016 12:47:32 +0200
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References: <nf5r01$klb$1@ger.gmane.org>	<20160420021101.GC8684@ad-mail.usersys.redhat.com>	<20160420115036.GG6517@noname.str.redhat.com>	<nf848r$jfe$1@ger.gmane.org>
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Subject: Re: [Qemu-devel] I/O errors reported to guest for raw-image-file
 backed /dev/vda - but host sees no I/O errors
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To: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org

On 04/21/2016 05:54 PM, Lutz Vieweg wrote:
> And indeed, the errors occured exactly at the time a backup procedure
> was preparing a read-only snapshot with "btrfs subvolume snapshot -r" -
> so until I can upgrade to a mainline kernel including the fix, I'll
> pause the qemu process while the "btrfs subvolume snapshot -r" runs.

Alas, this seems not to be sufficient to get rid of the symptom easily -
I guess that some of the "pwrite"s are executed asynchronously, at
a time when the qemu emulation is already in "pause" mode.

Will retry with some safeguard sleep time between the "stop" to
the monitor and the creation of the snapshot.

Regards,

Lutz Vieweg