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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-10-11 at 19:27 +0100, Konrad Rzeszutek Wilk wrote:
> On Mon, Oct 10, 2011 at 03:58:42PM -0400, Konrad Rzeszutek Wilk wrote:
> > On Mon, Oct 10, 2011 at 01:50:11PM -0400, Konrad Rzeszutek Wilk wrote:
> 
> Per Ian and Jan's suggestion (note, the structure is 4-byte aligned
> so we do not need to pad it):
> 
> # HG changeset patch
> # Parent 72f339bc600d7a9629d3f9eb8a279fbf8be25b12
> 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. Also update the description
> to mention the other parameters that the frontend can query the
> backend for: discard-aligment, discard-granularity, and
> discard-secure. We also utilize per Jan Beulich keen suggestion,
> the 8-bit reserved field to use as a flag value. Currently the only
> flag that can be passed for a discard operation is secure delete:
> BLKIF_OP_DISCARD_FLAG_SECURE.

This change seems to be conflating a large rename with new data fields,
changes to the documentation in the comments and other bits and bobs,
which makes it pretty hard to review it's actual impact. Can we get them
separately?

Ian.

> 
> CC: lidongyang@xxxxxxxxxx
> CC: owen.smith@xxxxxxxxxx
> CC: Pasi KÃrkkÃinen <pasik@xxxxxx>
> CC: JBeulich@xxxxxxxxxx
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> diff -r 72f339bc600d xen/include/public/io/blkif.h
> --- a/xen/include/public/io/blkif.h   Mon Oct 10 11:21:51 2011 +0100
> +++ b/xen/include/public/io/blkif.h   Tue Oct 11 14:10:33 2011 -0400
> @@ -82,26 +82,47 @@
>   */
>  #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. However, discard does not guarantee that the blocks
> + * will be erased from the device - it is just a hint to the device
> + * controller that these blocks are no longer in use. What the device
> + * controller does with that information is left to the controller.
> + * Discard operations are passed with sector_number as the
> + * 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
> + * The backend can optionally provide three extra XenBus attributes to
> + * further optimize the discard functionality:
> + * 'discard-aligment' - Devices that support discard functionality may
> + * internally allocate space in units that are bigger than the exported
> + * logical block size. The discard-alignment parameter indicates how many 
> bytes
> + * the beginning of the partition is offset from the internal allocation 
> unit's
> + * natural alignment.
> + * 'discard-granularity'  - Devices that support discard functionality may
> + * internally allocate space using units that are bigger than the logical 
> block
> + * size. The discard-granularity parameter indicates the size of the internal
> + * allocation unit in bytes if reported by the device. Otherwise the
> + * discard-granularity will be set to match the device's physical block size.
> + * 'discard-secure' - All copies of the discarded sectors (potentially 
> created by
> + * garbage collection) must also be erased.
>   */
> -#define BLKIF_OP_TRIM              5
> -
> +#define BLKIF_OP_DISCARD           5
>  /*
>   * Maximum scatter/gather segments per request.
>   * This is carefully chosen so that sizeof(blkif_ring_t) <= PAGE_SIZE.
> @@ -134,18 +155,20 @@ struct blkif_request {
>  typedef struct blkif_request blkif_request_t;
>  
>  /*
> - * Cast to this structure when blkif_request.operation == BLKIF_OP_TRIM
> - * sizeof(struct blkif_request_trim) <= sizeof(struct blkif_request)
> + * Cast to this structure when blkif_request.operation == BLKIF_OP_DISCARD
> + * sizeof(struct blkif_request_discard) <= sizeof(struct blkif_request)
>   */
> -struct blkif_request_trim {
> -    uint8_t        operation;    /* BLKIF_OP_TRIM                        */
> -    uint8_t        reserved;     /*                                      */
> +struct blkif_request_discard {
> +    uint8_t        operation;    /* BLKIF_OP_DISCARD                     */
> +                                 /* ignored if 'discard-secure=0'        */
> +#define BLKIF_OP_DISCARD_FLAG_SECURE (1<<0)
> +    uint8_t        flag;         /* BLKIF_OP_DISCARD_FLAG_SECURE or 0    */
>      blkif_vdev_t   handle;       /* same as for read/write requests      */
>      uint64_t       id;           /* private guest value, echoed in resp  */
>      blkif_sector_t sector_number;/* start sector idx on disk             */
>      uint64_t       nr_sectors;   /* number of contiguous sectors to trim */
>  };
> -typedef struct blkif_request_trim blkif_request_trim_t;
> +typedef struct blkif_request_discard blkif_request_discard_t;
>  
>  struct blkif_response {
>      uint64_t        id;              /* copied from request */



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