[Xen-devel] [PATCH 2/2 xen/stable-2.6.32.x] Add trim operation to xen block devices

[Owen Smith <owen.smith@xxxxxxxxxx>]

Defines the trim operation code, data structure and adds it to the
blk ring protocol. Blkback responds to trim operations with a
BLKIF_RSP_EOPNOTSUPP instead of using the default response, which logs
the operation as failed in the error log file.

Trim commands 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:
http://t13.org/Documents/UploadedDocuments/docs2008/
      e07154r6-Data_Set_Management_Proposal_for_ATA-ACS2.doc

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
---
 drivers/xen/blkback/blkback.c    |    7 +++++++
 include/xen/interface/io/blkif.h |   17 +++++++++++++++++
 2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/blkback/blkback.c b/drivers/xen/blkback/blkback.c
index b45b21f..03cb8f6 100644
--- a/drivers/xen/blkback/blkback.c
+++ b/drivers/xen/blkback/blkback.c
@@ -367,6 +367,13 @@ static int do_block_io_op(blkif_t *blkif)
                        blkif->st_wr_req++;
                        dispatch_rw_block_io(blkif, &req, pending_req);
                        break;
+               case BLKIF_OP_TRIM:
+                       /* respond with BLKIF_RSP_EOPNOTSUPP to reduce logging
+                        * from default case */
+                       make_response(blkif, req.id, req.operation,
+                                     BLKIF_RSP_EOPNOTSUPP);
+                       free_req(pending_req);
+                       break;
                default:
                        /* A good sign something is wrong: sleep for a while to
                         * avoid excessive CPU consumption by a bad guest. */
diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index 61e523a..1098d0c 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -43,6 +43,17 @@ typedef uint64_t blkif_sector_t;
  * create the "feature-barrier" node!
  */
 #define BLKIF_OP_WRITE_BARRIER     2
+/*
+ * Recognised only if "feature-trim" is present in backend xenbus info.
+ * The "feature-trim" node contains a boolean indicating whether barrier
+ * 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
 
 /*
  * Maximum scatter/gather segments per request.
@@ -61,6 +72,11 @@ struct blkif_request_rw {
        } seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 };
 
+struct blkif_request_trim {
+       blkif_sector_t sector_number;
+       uint64_t nr_sectors;
+};
+
 struct blkif_request {
        uint8_t        operation;    /* BLKIF_OP_???                         */
        uint8_t        nr_segments;  /* number of segments                   */
@@ -68,6 +84,7 @@ struct blkif_request {
        uint64_t       id;           /* private guest value, echoed in resp  */
        union {
                struct blkif_request_rw rw;
+               struct blkif_request_trim trim;
        } u;
 };
 
-- 
1.5.6.5


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