f95fd16f8d
4757 ZFS embedded-data block pointers ("zero block compression")
4913 zfs release should not be subject to space checks
MFC after: 2 weeks
74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
/*
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* CDDL HEADER START
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*
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* This file and its contents are supplied under the terms of the
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* Common Development and Distribution License ("CDDL"), version 1.0.
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* You may only use this file in accordance with the terms of version
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* 1.0 of the CDDL.
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*
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* A full copy of the text of the CDDL should have accompanied this
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* source. A copy of the CDDL is also available via the Internet at
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* http://www.illumos.org/license/CDDL.
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*
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* CDDL HEADER END
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*/
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/*
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* Copyright (c) 2013 by Delphix. All rights reserved.
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*/
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/*
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* Embedded-data Block Pointers
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*
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* Normally, block pointers point (via their DVAs) to a block which holds data.
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* If the data that we need to store is very small, this is an inefficient
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* use of space, because a block must be at minimum 1 sector (typically 512
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* bytes or 4KB). Additionally, reading these small blocks tends to generate
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* more random reads.
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*
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* Embedded-data Block Pointers allow small pieces of data (the "payload",
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* up to 112 bytes) to be stored in the block pointer itself, instead of
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* being pointed to. The "Pointer" part of this name is a bit of a
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* misnomer, as nothing is pointed to.
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*
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* BP_EMBEDDED_TYPE_DATA block pointers allow highly-compressible data to
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* be embedded in the block pointer. The logic for this is handled in
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* the SPA, by the zio pipeline. Therefore most code outside the zio
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* pipeline doesn't need special-cases to handle these block pointers.
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*
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* See spa.h for details on the exact layout of embedded block pointers.
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*/
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/*
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* buf must be at least BPE_GET_PSIZE(bp) bytes long (which will never be
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* more than BPE_PAYLOAD_SIZE bytes).
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*/
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void
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decode_embedded_bp_compressed(const blkptr_t *bp, void *buf)
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{
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int psize;
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uint8_t *buf8 = buf;
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uint64_t w = 0;
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const uint64_t *bp64 = (const uint64_t *)bp;
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ASSERT(BP_IS_EMBEDDED(bp));
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psize = BPE_GET_PSIZE(bp);
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/*
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* Decode the words of the block pointer into the byte array.
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* Low bits of first word are the first byte (little endian).
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*/
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for (int i = 0; i < psize; i++) {
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if (i % sizeof (w) == 0) {
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/* beginning of a word */
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ASSERT3P(bp64, <, bp + 1);
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w = *bp64;
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bp64++;
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if (!BPE_IS_PAYLOADWORD(bp, bp64))
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bp64++;
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}
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buf8[i] = BF64_GET(w, (i % sizeof (w)) * NBBY, NBBY);
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}
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}
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