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#include <sys/zfs_context.h>
21#include <sys/zio.h>
22#include <sys/zio_compress.h>
23
24/*
25 * Embedded-data Block Pointers
26 *
27 * Normally, block pointers point (via their DVAs) to a block which holds data.
28 * If the data that we need to store is very small, this is an inefficient
29 * use of space, because a block must be at minimum 1 sector (typically 512
30 * bytes or 4KB).  Additionally, reading these small blocks tends to generate
31 * more random reads.
32 *
33 * Embedded-data Block Pointers allow small pieces of data (the "payload",
34 * up to 112 bytes) to be stored in the block pointer itself, instead of
35 * being pointed to.  The "Pointer" part of this name is a bit of a
36 * misnomer, as nothing is pointed to.
37 *
38 * BP_EMBEDDED_TYPE_DATA block pointers allow highly-compressible data to
39 * be embedded in the block pointer.  The logic for this is handled in
40 * the SPA, by the zio pipeline.  Therefore most code outside the zio
41 * pipeline doesn't need special-cases to handle these block pointers.
42 *
43 * See spa.h for details on the exact layout of embedded block pointers.
44 */
45
46void
47encode_embedded_bp_compressed(blkptr_t *bp, void *data,
48    enum zio_compress comp, int uncompressed_size, int compressed_size)
49{
50	uint64_t *bp64 = (uint64_t *)bp;
51	uint64_t w = 0;
52	uint8_t *data8 = data;
53
54	ASSERT3U(compressed_size, <=, BPE_PAYLOAD_SIZE);
55	ASSERT(uncompressed_size == compressed_size ||
56	    comp != ZIO_COMPRESS_OFF);
57	ASSERT3U(comp, >=, ZIO_COMPRESS_OFF);
58	ASSERT3U(comp, <, ZIO_COMPRESS_FUNCTIONS);
59
60	bzero(bp, sizeof (*bp));
61	BP_SET_EMBEDDED(bp, B_TRUE);
62	BP_SET_COMPRESS(bp, comp);
63	BP_SET_BYTEORDER(bp, ZFS_HOST_BYTEORDER);
64	BPE_SET_LSIZE(bp, uncompressed_size);
65	BPE_SET_PSIZE(bp, compressed_size);
66
67	/*
68	 * Encode the byte array into the words of the block pointer.
69	 * First byte goes into low bits of first word (little endian).
70	 */
71	for (int i = 0; i < compressed_size; i++) {
72		BF64_SET(w, (i % sizeof (w)) * NBBY, NBBY, data8[i]);
73		if (i % sizeof (w) == sizeof (w) - 1) {
74			/* we've reached the end of a word */
75			ASSERT3P(bp64, <, bp + 1);
76			*bp64 = w;
77			bp64++;
78			if (!BPE_IS_PAYLOADWORD(bp, bp64))
79				bp64++;
80			w = 0;
81		}
82	}
83	/* write last partial word */
84	if (bp64 < (uint64_t *)(bp + 1))
85		*bp64 = w;
86}
87
88/*
89 * buf must be at least BPE_GET_PSIZE(bp) bytes long (which will never be
90 * more than BPE_PAYLOAD_SIZE bytes).
91 */
92void
93decode_embedded_bp_compressed(const blkptr_t *bp, void *buf)
94{
95	int psize;
96	uint8_t *buf8 = buf;
97	uint64_t w = 0;
98	const uint64_t *bp64 = (const uint64_t *)bp;
99
100	ASSERT(BP_IS_EMBEDDED(bp));
101
102	psize = BPE_GET_PSIZE(bp);
103
104	/*
105	 * Decode the words of the block pointer into the byte array.
106	 * Low bits of first word are the first byte (little endian).
107	 */
108	for (int i = 0; i < psize; i++) {
109		if (i % sizeof (w) == 0) {
110			/* beginning of a word */
111			ASSERT3P(bp64, <, bp + 1);
112			w = *bp64;
113			bp64++;
114			if (!BPE_IS_PAYLOADWORD(bp, bp64))
115				bp64++;
116		}
117		buf8[i] = BF64_GET(w, (i % sizeof (w)) * NBBY, NBBY);
118	}
119}
120