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
46 void
encode_embedded_bp_compressed(blkptr_t * bp,void * data,enum zio_compress comp,int uncompressed_size,int compressed_size)47 encode_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 */
92 void
decode_embedded_bp_compressed(const blkptr_t * bp,void * buf)93 decode_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