module/zfs/blkptr.c

   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, 2016 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
  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
  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
 121 /*
 122  * Fill in the buffer with the (decompressed) payload of the embedded
 123  * blkptr_t.  Takes into account compression and byteorder (the payload is
 124  * treated as a stream of bytes).
 125  * Return 0 on success, or ENOSPC if it won't fit in the buffer.
 126  */
 127 int
 128 decode_embedded_bp(const blkptr_t *bp, void *buf, int buflen)
 129 {
 130         int lsize, psize;
 131
 132         ASSERT(BP_IS_EMBEDDED(bp));
 133
 134         lsize = BPE_GET_LSIZE(bp);
 135         psize = BPE_GET_PSIZE(bp);
 136
 137         if (lsize > buflen)
 138                 return (SET_ERROR(ENOSPC));
 139         ASSERT3U(lsize, ==, buflen);
 140
 141         if (BP_GET_COMPRESS(bp) != ZIO_COMPRESS_OFF) {
 142                 uint8_t dstbuf[BPE_PAYLOAD_SIZE];
 143                 decode_embedded_bp_compressed(bp, dstbuf);
 144                 VERIFY0(zio_decompress_data_buf(BP_GET_COMPRESS(bp),
 145                     dstbuf, buf, psize, buflen));
 146         } else {
 147                 ASSERT3U(lsize, ==, psize);
 148                 decode_embedded_bp_compressed(bp, buf);
 149         }
 150
 151         return (0);
 152 }