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Re: [Xen-devel] [PATCH 2/2] Add trim operation to xen block devices

To: Owen Smith <owen.smith@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/2] Add trim operation to xen block devices
From: Keir Fraser <keir@xxxxxxx>
Date: Tue, 21 Dec 2010 18:05:57 +0000
Cc:
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Thread-topic: [Xen-devel] [PATCH 2/2] Add trim operation to xen block devices
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On 21/12/2010 16:58, "Owen Smith" <owen.smith@xxxxxxxxxx> wrote:

> +/*
> + * Recognised only if "feature-trim" is present in backend xenbus info.
> + * The "feature-trim" node contains a boolean indicating whether trim
> + * requests are likely to succeed or fail. Either way, a trim request
> + * may fail at any time with BLKIF_RSP_EOPNOTSUPP if it is unsupported by
> + * the underlying block-device hardware. The boolean simply indicates whether
> + * or not it is worthwhile for the frontend to attempt trim requests.
> + * If a backend does not recognise BLKIF_OP_TRIM, it should *not*
> + * create the "feature-trim" node!
> + */
> +#define BLKIF_OP_TRIM              4

What is a 'trim operation'? It's not documented in the patch description(s)
or in the protocol-defining header file.

 -- Keir



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