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 */ 46 void 47 decode_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