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Re: [PATCH] hw/block/nvme: add block utilization tracking

From: Keith Busch
Subject: Re: [PATCH] hw/block/nvme: add block utilization tracking
Date: Wed, 14 Oct 2020 10:05:13 -0700

On Wed, Oct 14, 2020 at 10:47:21AM +0200, Klaus Jensen wrote:
> On Oct 13 14:06, Keith Busch wrote:
> > If we were going to support it here, wouldn't it make more sense to
> > tie it to the filesystem's ability to support fallocate hole punch for
> > the backing namespace, and check if the range is allocated with
> > SEEK_HOLE?  Then you don't even need to track persistent state, and
> > we're actually getting the genuine capability.
> > 
> Yes, this would be optimal, definitely. I think we have to rely on what
> we can do with the QEMU block layer, so please see my v2 that uses
> bdrv_block_status. I did do something like this initially, but was
> unsure if we could live with the fact that block drivers such as qcow2
> cannot honor a discard unless an entire cluster is discard/zeroed.
> But see my commit message, I think we can work with it and still be in
> compliance with the spec.

Yes, I think that's better, though I'm not familiar with that particular
API. I definitely prefer implementing spec features in useful ways that
work with other layers rather than faking it.

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