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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 21.12.10 at 17:58, Owen Smith <owen.smith@xxxxxxxxxx> wrote:
> --- a/xen/include/public/io/blkif.h   Tue Dec 21 13:28:48 2010 +0000
> +++ b/xen/include/public/io/blkif.h   Tue Dec 21 13:30:16 2010 +0000
> @@ -76,6 +76,17 @@
>   * "feature-flush-cache" node!
>   */
>  #define BLKIF_OP_FLUSH_DISKCACHE   3
> +/*
> + * 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

I wonder if it would be possible to skip 4 here. We've been carrying
a patch to support packet commands (for CD-ROM support) for
quite a while, using 4 for BLKIF_OP_PACKET. I realize this should
have been presented on the list long ago, but unfortunately the
author never did and is no longer with the company. While I could
submit the kernel side patches, I wouldn't be able to advocate for
them, partly because I don't know all of the details, partly because
there are some rough edges (Linux-isms introduced into
xen/include/public/io/), and partly because backend support exists
only for blktap1 so far.

An alternative to submitting the full patch set would be to just
submit a patch adding the necessary definition here - given that
BLKIF_OP_FLUSH_DISKCACHE too looks like a half-baked thing
only (used exclusively in mini-os' blkfront and qemu's block-vbd;
I wasn't able to locate what backend might actually handle it),
would this be acceptable?

Thanks, Jan


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