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Re: [Qemu-block] Broken aarch64 by qcow2: skip writing zero buffers to e

From: Anton Nefedov
Subject: Re: [Qemu-block] Broken aarch64 by qcow2: skip writing zero buffers to empty COW areas [v2]
Date: Wed, 21 Aug 2019 15:49:23 +0000

On 21/8/2019 5:14 PM, Lukáš Doktor wrote:
> Hello guys,
> First attempt was rejected due to zip attachment, let's try it again with 
> just Avocado-vt debug.log and serial console log files attached.
> I bisected a regression on aarch64 all the way to this commit: "qcow2: skip 
> writing zero buffers to empty COW areas" 
> c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a. Would you please have a look at it?
> My reproducer is running kickstart installation of RHEL-8 from DVD on aarch64 
> gicv3 machine, which never finishes since this commit, where anaconda 
> complains about package installation, occasionally there are also XFS 
> metadata corruption messages on serial console:


this looks scary :( I doubt that it can have anything to do with aarch64
but rather a really tricky timing (or, possibly, a broken environment
like broken fallocate() on a host? who knows..)

Is it always the same machine you observe this issue on? Did you try

I just wonder if it's worth to try to reproduce it on my machine
(and I don't have aarch64 on hand now). I can probably come up with
some torture test that will continuously write to qcow2 with random
offsets/sizes and verify the result.

If you could kindly reproduce it again then we can probably start with
enabling qemu traces by appending
  " -trace bdrv* -trace qcow2* -trace file=/some_huge_partition/qemu.log"
to the command line.

Beware that it's going to produce a huge amount of logs.

Also, the corrupted image and the serial log will be required for



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