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Re: [Qemu-devel] [PATCH 06/12] nbd: support NBD_CMD_TRIM in the server

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH 06/12] nbd: support NBD_CMD_TRIM in the server
Date: Wed, 14 Sep 2011 18:25:59 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2

On 09/14/2011 05:44 PM, Christoph Hellwig wrote:
Map it to bdrv_discard.  The server can now expose NBD_FLAG_SEND_TRIM.

Note that discard support without a way to communicate the alignment/size

Yep, especially because alignment can be as small as 512 for sparse raw, and as high as 65536 for qcow2...

and without the discard_zeroes_data flag is pretty much

... but right now in QEMU it is most useful with qcow2, so !discard_zeroes_data is pretty much the best you can do.

In general, QEMU's block layer does not really do much to pass information on discard features, which is why I didn't think much about these bits. I'm interested in making NBD as featureful as the QEMU block layer, but beyond that not much. :)

Still you're obviously right, I'll talk to upstream.


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