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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 5 of 5] blkif.h: Define and document the request number/size/segments extension
xen/include/public/io/blkif.h | 106 ++++++++++++++++++++++++++++++++++++++++-
1 files changed, 103 insertions(+), 3 deletions(-)
Note: The definition of BLKIF_MAX_SEGMENTS_PER_REQUEST has changed.
Drivers must be updated to, at minimum, use
BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK, before being compatible
with this header file.
This extension first appeared in FreeBSD.
Signed-off-by: Justin T. Gibbs <justing@xxxxxxxxxxxxxxxx>
diff -r c3609ad53946 -r f5c2e866c661 xen/include/public/io/blkif.h
--- a/xen/include/public/io/blkif.h Thu Feb 02 16:19:57 2012 -0700
+++ b/xen/include/public/io/blkif.h Thu Feb 02 16:19:57 2012 -0700
@@ -119,6 +119,29 @@
* The maximum supported size of the request ring buffer in units of
* machine pages. The value must be a power of 2.
*
+ * max-requests <uint32_t>
+ * Default Value: BLKIF_MAX_RING_REQUESTS(PAGE_SIZE)
+ * Maximum Value: BLKIF_MAX_RING_REQUESTS(PAGE_SIZE * max-ring-pages)
+ *
+ * The maximum number of concurrent requests supported by the backend.
+ *
+ * max-request-segments
+ * Values: <uint8_t>
+ * Default Value: BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK
+ * Maximum Value: 255
+ *
+ * The maximum value of blkif_request.nr_segments supported by
+ * the backend.
+ *
+ * max-request-size
+ * Values: <uint32_t>
+ * Default Value: BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK * PAGE_SIZE
+ * Maximum Value: 255 * PAGE_SIZE
+ *
+ * The maximum amount of data, in bytes, that can be referenced by a
+ * request type that accesses frontend memory (currently BLKIF_OP_READ,
+ * BLKIF_OP_WRITE, or BLKIF_OP_WRITE_BARRIER).
+ *
*----------------------- Backend Device Identification -----------------------
* mode
* Values: "r" (read only), "w" (writable)
@@ -235,6 +258,31 @@
* The size of the frontend allocated request ring buffer in units of
* machine pages. The value must be a power of 2.
*
+ * max-requests
+ * Values: <uint32_t>
+ * Default Value: BLKIF_MAX_RING_REQUESTS(PAGE_SIZE)
+ * Maximum Value: BLKIF_MAX_RING_REQUESTS(PAGE_SIZE * max-ring_pages)
+ *
+ * The maximum number of concurrent requests that will be issued by
+ * the frontend.
+ *
+ * max-request-segments
+ * Values: <uint8_t>
+ * Default Value: BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK
+ * Maximum Value: MIN(255, backend/max-request-segments)
+ *
+ * The maximum value the frontend will set in the
+ * blkif_request.nr_segments field.
+ *
+ * max-request-size
+ * Values: <uint32_t>
+ * Default Value: BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK * PAGE_SIZE
+ * Maximum Value: max-request-segments * PAGE_SIZE
+ *
+ * The maximum amount of data, in bytes, that can be referenced by
+ * a request type that accesses frontend memory (currently BLKIF_OP_READ,
+ * BLKIF_OP_WRITE, or BLKIF_OP_WRITE_BARRIER).
+ *
*------------------------- Virtual Device Properties -------------------------
*
* device-type
@@ -392,11 +440,21 @@
#define BLKIF_OP_DISCARD 5
/*
- * Maximum scatter/gather segments per request.
+ * Maximum scatter/gather segments associated with a request header block.
* This is carefully chosen so that sizeof(blkif_ring_t) <= PAGE_SIZE.
* NB. This could be 12 if the ring indexes weren't stored in the same page.
*/
-#define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
+#define BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK 11
+
+/*
+ * Maximum scatter/gather segments associated with a segment block.
+ */
+#define BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK 14
+
+/*
+ * Maximum scatter/gather segments per request (header + segment blocks).
+ */
+#define BLKIF_MAX_SEGMENTS_PER_REQUEST 255
/*
* NB. first_sect and last_sect in blkif_request_segment, as well as
@@ -411,9 +469,25 @@ struct blkif_request_segment {
/* @last_sect: last sector in frame to transfer (inclusive). */
uint8_t first_sect, last_sect;
};
+typedef struct blkif_request_segment blkif_request_segment_t;
/*
* Starting ring element for any I/O request.
+ *
+ * One or more segment blocks can be inserted into the request ring
+ * just after a blkif_request_t, allowing requests to operate on
+ * up to BLKIF_MAX_SEGMENTS_PER_REQUEST.
+ *
+ * BLKIF_SEGS_TO_BLOCKS() can be used on blkif_requst.nr_segments
+ * to determine the number of contiguous ring entries associated
+ * with this request.
+ *
+ * Note: Due to the way Xen request rings operate, the producer and
+ * consumer indices of the ring must be incremented by the
+ * BLKIF_SEGS_TO_BLOCKS() value of the associated request.
+ * (e.g. a response to a 3 ring entry request must also consume
+ * 3 entries in the ring, even though only the first ring entry
+ * in the response has any data.)
*/
struct blkif_request {
uint8_t operation; /* BLKIF_OP_??? */
@@ -421,11 +495,22 @@ struct blkif_request {
blkif_vdev_t handle; /* only for read/write requests */
uint64_t id; /* private guest value, echoed in resp */
blkif_sector_t sector_number;/* start sector idx on disk (r/w only) */
- struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ blkif_request_segment_t seg[BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK];
};
typedef struct blkif_request blkif_request_t;
/*
+ * A segment block is a ring request structure that contains only
+ * segment data.
+ *
+ * sizeof(struct blkif_segment_block) <= sizeof(struct blkif_request)
+ */
+struct blkif_segment_block {
+ blkif_request_segment_t seg[BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK];
+};
+typedef struct blkif_segment_block blkif_segment_block_t;
+
+/*
* Cast to this structure when blkif_request.operation == BLKIF_OP_DISCARD
* sizeof(struct blkif_request_discard) <= sizeof(struct blkif_request)
*/
@@ -462,6 +547,21 @@ typedef struct blkif_response blkif_resp
*/
DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
+/*
+ * Index to, and treat as a segment block, an entry in the ring.
+ */
+#define BLKRING_GET_SEG_BLOCK(_r, _idx) \
+ (((blkif_segment_block_t *)RING_GET_REQUEST(_r, _idx))->seg)
+
+/*
+ * The number of ring request blocks required to handle an I/O
+ * request containing _segs segments.
+ */
+#define BLKIF_SEGS_TO_BLOCKS(_segs) \
+ ((((_segs - BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK) \
+ + (BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK - 1)) \
+ / BLKIF_MAX_SEGMENTS_PER_SEGMENT_BLOCK) + /*header_block*/1)
+
#define VDISK_CDROM 0x1
#define VDISK_REMOVABLE 0x2
#define VDISK_READONLY 0x4
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