[Xen-devel] Re: [PATCH 1 of 1] interface: BLKIF_OP_TRIM -> BLKIF_OP_DISCARD

[Li Dongyang <lidongyang@xxxxxxxxxx>]

On Wed, Aug 31, 2011 at 11:40 AM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> # HG changeset patch
> # User Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> # Date 1314761891 14400
> # Node ID d2538ec1df2b9f4c39978d96ebe3bccccb068ad0
> # Parent  ac9aa65050e9abc8f1c12c8603acf3b99e22cddc
> interface: BLKIF_OP_TRIM -> BLKIF_OP_DISCARD
>
> The name 'trim' is specific to the ATA discard implementation.
> The name 'scsi unmap' is specific to the SCSI discard implementation.
>
> We should really use a generic name - and the name 'discard'
> looks to be the most generic of them all.
>
> CC: lidongyang@xxxxxxxxxx
> CC: owen.smith@xxxxxxxxxx
> CC: Pasi Kärkkäinen <pasik@xxxxxx>
> CC: JBeulich@xxxxxxxxxx
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>
> diff -r ac9aa65050e9 -r d2538ec1df2b xen/include/public/io/blkif.h
> --- a/xen/include/public/io/blkif.h     Tue Aug 30 11:46:58 2011 +0100
> +++ b/xen/include/public/io/blkif.h     Tue Aug 30 23:38:11 2011 -0400
> @@ -82,25 +82,29 @@
>  */
>  #define BLKIF_OP_RESERVED_1        4
>  /*
> - * 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
> + * Recognised only if "feature-discard" is present in backend xenbus info.
> + * The "feature-discard" node contains a boolean indicating whether trim
> + * (ATA) or unmap (SCSI) - conviently called discard requests are likely
> + * to succeed or fail. Either way, a discard 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!
> - *
> - * Trim operation is a request for the underlying block device to mark
> - * extents to be erased. Trim operations are passed with sector_number as the
> - * sector index to begin trim operations at and nr_sectors as the number of
> - * sectors to be trimmed. The specified sectors should be trimmed if the
> - * underlying block device supports trim operations, or a 
> BLKIF_RSP_EOPNOTSUPP
> - * should be returned. More information about trim operations at:
> + * or not it is worthwhile for the frontend to attempt discard requests.
> + * If a backend does not recognise BLKIF_OP_DISCARD, it should *not*
> + * create the "feature-discard" node!
> + *
> + * Discard operation is a request for the underlying block device to mark
> + * extents to be erased. Discard operations are passed with sector_number as 
> the
well I think we need to change the comments here, discard doesn't
guarantee the blocks
will be erased from the device, it's just a hint to the device
controller these blocks are no longer
used, and what to do with these blocks are left to the device
controller, on an SSD the controller
might erase them and use the blank blocks to do some optimization like
gc and better wear leveling.

and for the novell driver, we are free to change to BLKIF_OP_DISCARD,
cause we have nothing depend
on BLKIF_OP_TRIM, and Jan should know better than me on this, correct
me if am wrong, Thanks.
> + * sector index to begin discard operations at and nr_sectors as the number 
> of
> + * sectors to be discarded. The specified sectors should be discarded if the
> + * underlying block device supports trim (ATA) or unmap (SCSI) operations,
> + * or a BLKIF_RSP_EOPNOTSUPP  should be returned.
> + * More information about trim/unmap operations at:
>  * http://t13.org/Documents/UploadedDocuments/docs2008/
>  *     e07154r6-Data_Set_Management_Proposal_for_ATA-ACS2.doc
> + * http://www.seagate.com/staticfiles/support/disc/manuals/
> + *     Interface%20manuals/100293068c.pdf
>  */
> -#define BLKIF_OP_TRIM              5
> +#define BLKIF_OP_DISCARD          5
>
>  /*
>  * Maximum scatter/gather segments per request.
>

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