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Re: [Qemu-devel] [Nbd] [PATCH v2] doc: Add NBD_CMD_BLOCK_STATUS extensio

From: Alex Bligh
Subject: Re: [Qemu-devel] [Nbd] [PATCH v2] doc: Add NBD_CMD_BLOCK_STATUS extension
Date: Mon, 4 Apr 2016 22:12:03 +0100

On 4 Apr 2016, at 21:34, Eric Blake <address@hidden> wrote:

> The original design abused the 16-bit 'flags' field of each command to
> instead try and treat that value as a bitmap number, instead of a
> bitwise-or'd set of flags.  That was one of the complaints against v1,
> and was fixed in v2 by having a single boolean flag, NBD_CMD_FLAG_DIRTY,
> which was off for (default) allocation queries, and set for dirtiness
> queries.  We can add other flags for any other type of queries, and the
> principle of each query being a run-length-encoded listing still applies.

Well abusing flags is pretty gross.

You're multiplexing on a single flag and I didn't like that.

So I suggested multiplexing on the command and you didn't like that.

Eventually as you point out we really want to expand the command field,
and ...

> As it is, we don't have structured writes - right now, you can write a

... I agree this is almost inventing 'structured writes' :-)

Alex Bligh

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