Re: Block alignment of qcow2 compress driver

[Richard W.M. Jones]

On Fri, Jan 28, 2022 at 12:39:11PM +0100, Hanna Reitz wrote:
> So I actually don’t know why it works for you.  OTOH, I don’t
> understand why the block size affects you over NBD, because I would
> have expected qemu to internally auto-align requests when they are
> not aligned (in bdrv_co_pwritev_part()).

I checked it again and my hack definitely fixes nbdcopy.  But maybe
that's expected if qemu-nbd is auto-aligning requests?  (I'm only
accessing the block layer through qemu-nbd, not with qemu-io)

> Like, when I set the NBD
> block driver’s alignment to 512[2], the following still succeeds:

Did you just patch that line in the code or is there a qemu-nbd
option/image-opts to do this?

Rich.

> [1] https://gitlab.com/qemu-project/qemu/-/blob/master/block/qcow2.c#L4662
> [2] https://gitlab.com/qemu-project/qemu/-/blob/master/block/nbd.c#L1918

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