[Xen-devel] Re: [PATCH 3 of 3] interface: add 'discard-secure' and BLKIF_DISCARD_SECURE

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2011-10-12 at 23:12 +0100, Konrad Rzeszutek Wilk wrote:
> # HG changeset patch
> # User Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> # Date 1318457231 14400
> # Node ID 50850daec7f0486ee7ca69b3d4cb58b4d340a5a7
> # Parent  15c2d70dbac3e31c2d74b6700e1bb5f8a7d8256e
> interface: add 'discard-secure' and BLKIF_DISCARD_SECURE
> 
> Alter the 'reserved' uint8_t to be used a 'flag'. We use only for
> one flag: BLKIF_DISCARD_SECURE.
> 
> That flag can only be set if the backend has set 'discard-secure' to one.
> If backend has not set 'discard-secure' to one, that flag will have no
> effect.
> 
> Acked-by: Jan Beulich <JBeulich@xxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> diff -r 15c2d70dbac3 -r 50850daec7f0 xen/include/public/io/blkif.h
> --- a/xen/include/public/io/blkif.h   Wed Oct 12 18:07:07 2011 -0400
> +++ b/xen/include/public/io/blkif.h   Wed Oct 12 18:07:11 2011 -0400
> @@ -107,7 +107,7 @@
>   *     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 two extra XenBus attributes to
> + * The backend can optionally provide three extra XenBus attributes to
                                         these

avoids patching (or more likely forgetting to patch) this line every
time we add an attribute.

>   * further optimize the discard functionality:
>   * 'discard-aligment' - Devices that support discard functionality may
>   * internally allocate space in units that are bigger than the exported
> @@ -119,6 +119,9 @@
>   * 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.  To use this feature, the flag
> + * BLKIF_DISCARD_SECURE must be set in the blkif_request_trim.

Stray "trim" here.

>   */
>  #define BLKIF_OP_DISCARD           5

It just occurred to me that if reusing the reserved field is going to
prove a problem we could have had BLKIF_OP_DISCARD_SECURE. I think we've
got things under control though.

>  
> @@ -159,7 +162,8 @@ typedef struct blkif_request blkif_reque
>   */
>  struct blkif_request_discard {
>      uint8_t        operation;    /* BLKIF_OP_DISCARD                     */
> -    uint8_t        reserved;     /*                                      */
> +    uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero         */
> +#define BLKIF_DISCARD_SECURE (1<<0)  /* ignored if discard-secure=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             */
> 
> 



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