From 927a13de6c85faa388eef1041baae17744be6791 Mon Sep 17 00:00:00 2001 From: Olaf Hering Date: Tue, 28 Jan 2014 13:33:57 +0100 Subject: [PATCH] blkif.h: enhance comments related to the discard feature Also fix the name of the discard-alignment property, add the missing 'n'. Signed-off-by: Olaf Hering Acked-by: Keir Fraser Acked-by: Konrad Rzeszutek Wilk --- xen/include/public/io/blkif.h | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/xen/include/public/io/blkif.h b/xen/include/public/io/blkif.h index 84eb7fdabc..542f1237a7 100644 --- a/xen/include/public/io/blkif.h +++ b/xen/include/public/io/blkif.h @@ -175,7 +175,7 @@ * *------------------------- Backend Device Properties ------------------------- * - * discard-aligment + * discard-alignment * Values: * Default Value: 0 * Notes: 4, 5 @@ -194,6 +194,7 @@ * discard-secure * Values: 0/1 (boolean) * Default Value: 0 + * Notes: 10 * * A value of "1" indicates that the backend can process BLKIF_OP_DISCARD * requests with the BLKIF_DISCARD_SECURE flag set. @@ -323,9 +324,15 @@ * For full interoperability, block front and backends should publish * identical ring parameters, adjusted for unit differences, to the * XenStore nodes used in both schemes. - * (4) Devices that support discard functionality may internally allocate - * space (discardable extents) in units that are larger than the - * exported logical block size. + * (4) Devices that support discard functionality may internally allocate space + * (discardable extents) in units that are larger than the exported logical + * block size. If the backing device has such discardable extents the + * backend should provide both discard-granularity and discard-alignment. + * Providing just one of the two may be considered an error by the frontend. + * Backends supporting discard should include discard-granularity and + * discard-alignment even if it supports discarding individual sectors. + * Frontends should assume discard-alignment == 0 and discard-granularity + * == sector size if these keys are missing. * (5) The discard-alignment parameter allows a physical device to be * partitioned into virtual devices that do not necessarily begin or * end on a discardable extent boundary. @@ -344,6 +351,8 @@ * grants that can be persistently mapped in the frontend driver, but * due to the frontent driver implementation it should never be bigger * than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST. + *(10) The discard-secure property may be present and will be set to 1 if the + * backing device supports secure discard. */ /* -- 2.30.2