blkptr.c revision 268649 
1/*
2 * CDDL HEADER START
3 *
4 * This file and its contents are supplied under the terms of the
5 * Common Development and Distribution License ("CDDL"), version 1.0.
6 * You may only use this file in accordance with the terms of version
7 * 1.0 of the CDDL.
8 *
9 * A full copy of the text of the CDDL should have accompanied this
10 * source.  A copy of the CDDL is also available via the Internet at
11 * http://www.illumos.org/license/CDDL.
12 *
13 * CDDL HEADER END
14 */
15
16/*
17 * Copyright (c) 2013 by Delphix. All rights reserved.
18 */
19
20/*
21 * Embedded-data Block Pointers
22 *
23 * Normally, block pointers point (via their DVAs) to a block which holds data.
24 * If the data that we need to store is very small, this is an inefficient
25 * use of space, because a block must be at minimum 1 sector (typically 512
26 * bytes or 4KB).  Additionally, reading these small blocks tends to generate
27 * more random reads.
28 *
29 * Embedded-data Block Pointers allow small pieces of data (the "payload",
30 * up to 112 bytes) to be stored in the block pointer itself, instead of
31 * being pointed to.  The "Pointer" part of this name is a bit of a
32 * misnomer, as nothing is pointed to.
33 *
34 * BP_EMBEDDED_TYPE_DATA block pointers allow highly-compressible data to
35 * be embedded in the block pointer.  The logic for this is handled in
36 * the SPA, by the zio pipeline.  Therefore most code outside the zio
37 * pipeline doesn't need special-cases to handle these block pointers.
38 *
39 * See spa.h for details on the exact layout of embedded block pointers.
40 */
41
42/*
43 * buf must be at least BPE_GET_PSIZE(bp) bytes long (which will never be
44 * more than BPE_PAYLOAD_SIZE bytes).
45 */
46void
47decode_embedded_bp_compressed(const blkptr_t *bp, void *buf)
48{
49	int psize;
50	uint8_t *buf8 = buf;
51	uint64_t w = 0;
52	const uint64_t *bp64 = (const uint64_t *)bp;
53
54	ASSERT(BP_IS_EMBEDDED(bp));
55
56	psize = BPE_GET_PSIZE(bp);
57
58	/*
59	 * Decode the words of the block pointer into the byte array.
60	 * Low bits of first word are the first byte (little endian).
61	 */
62	for (int i = 0; i < psize; i++) {
63		if (i % sizeof (w) == 0) {
64			/* beginning of a word */
65			ASSERT3P(bp64, <, bp + 1);
66			w = *bp64;
67			bp64++;
68			if (!BPE_IS_PAYLOADWORD(bp, bp64))
69				bp64++;
70		}
71		buf8[i] = BF64_GET(w, (i % sizeof (w)) * NBBY, NBBY);
72	}
73}
74