ocfs2: Add the underlying blockcheck code.

This is the code that computes crc32 and ecc for ocfs2 metadata blocks.
There are high-level functions that check whether the filesystem has the
ecc feature, mid-level functions that work on a single block or array of
buffer_heads, and the low-level ecc hamming code that can handle
multiple buffers like crc32_le().

It's not hooked up to the filesystem yet.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 480 insertions, 0 deletions

diff --git a/fs/ocfs2/blockcheck.c b/fs/ocfs2/blockcheck.c
new file mode 100644
index 000000000000..2bf3d7f61aec
--- /dev/null
+++ b/fs/ocfs2/blockcheck.c
@@ -0,0 +1,480 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * blockcheck.c
+ *
+ * Checksum and ECC codes for the OCFS2 userspace library.
+ *
+ * Copyright (C) 2006, 2008 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License, version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/crc32.h>
+#include <linux/buffer_head.h>
+#include <linux/bitops.h>
+#include <asm/byteorder.h>
+
+#include "ocfs2.h"
+
+#include "blockcheck.h"
+
+
+
+/*
+ * We use the following conventions:
+ *
+ * d = # data bits
+ * p = # parity bits
+ * c = # total code bits (d + p)
+ */
+static int calc_parity_bits(unsigned int d)
+{
+        unsigned int p;
+
+        /*
+         * Bits required for Single Error Correction is as follows:
+         *
+         * d + p + 1 <= 2^p
+         *
+         * We're restricting ourselves to 31 bits of parity, that should be
+         * sufficient.
+         */
+        for (p = 1; p < 32; p++)
+        {
+                if ((d + p + 1) <= (1 << p))
+                        return p;
+        }
+
+        return 0;
+}
+
+/*
+ * Calculate the bit offset in the hamming code buffer based on the bit's
+ * offset in the data buffer.  Since the hamming code reserves all
+ * power-of-two bits for parity, the data bit number and the code bit
+ * number are offest by all the parity bits beforehand.
+ *
+ * Recall that bit numbers in hamming code are 1-based.  This function
+ * takes the 0-based data bit from the caller.
+ *
+ * An example.  Take bit 1 of the data buffer.  1 is a power of two (2^0),
+ * so it's a parity bit.  2 is a power of two (2^1), so it's a parity bit.
+ * 3 is not a power of two.  So bit 1 of the data buffer ends up as bit 3
+ * in the code buffer.
+ */
+static unsigned int calc_code_bit(unsigned int i)
+{
+        unsigned int b, p;
+
+        /*
+         * Data bits are 0-based, but we're talking code bits, which
+         * are 1-based.
+         */
+        b = i + 1;
+
+        /*
+         * For every power of two below our bit number, bump our bit.
+         *
+         * We compare with (b + 1) becuase we have to compare with what b
+         * would be _if_ it were bumped up by the parity bit.  Capice?
+         */
+        for (p = 0; (1 << p) < (b + 1); p++)
+                b++;
+
+        return b;
+}
+
+/*
+ * This is the low level encoder function.  It can be called across
+ * multiple hunks just like the crc32 code.  'd' is the number of bits
+ * _in_this_hunk_.  nr is the bit offset of this hunk.  So, if you had
+ * two 512B buffers, you would do it like so:
+ *
+ * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
+ * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
+ *
+ * If you just have one buffer, use ocfs2_hamming_encode_block().
+ */
+u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
+{
+        unsigned int p = calc_parity_bits(nr + d);
+        unsigned int i, j, b;
+
+        BUG_ON(!p);
+
+        /*
+         * b is the hamming code bit number.  Hamming code specifies a
+         * 1-based array, but C uses 0-based.  So 'i' is for C, and 'b' is
+         * for the algorithm.
+         *
+         * The i++ in the for loop is so that the start offset passed
+         * to ocfs2_find_next_bit_set() is one greater than the previously
+         * found bit.
+         */
+        for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
+        {
+                /*
+                 * i is the offset in this hunk, nr + i is the total bit
+                 * offset.
+                 */
+                b = calc_code_bit(nr + i);
+
+                for (j = 0; j < p; j++)
+                {
+                        /*
+                         * Data bits in the resultant code are checked by
+                         * parity bits that are part of the bit number
+                         * representation.  Huh?
+                         *
+                         * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
+                         * In other words, the parity bit at position 2^k
+                         * checks bits in positions having bit k set in
+                         * their binary representation.  Conversely, for
+                         * instance, bit 13, i.e. 1101(2), is checked by
+                         * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
+                         * </wikipedia>
+                         *
+                         * Note that 'k' is the _code_ bit number.  'b' in
+                         * our loop.
+                         */
+                        if (b & (1 << j))
+                                parity ^= (1 << j);
+                }
+        }
+
+        /* While the data buffer was treated as little endian, the
+         * return value is in host endian. */
+        return parity;
+}
+
+u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
+{
+        return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
+}
+
+/*
+ * Like ocfs2_hamming_encode(), this can handle hunks.  nr is the bit
+ * offset of the current hunk.  If bit to be fixed is not part of the
+ * current hunk, this does nothing.
+ *
+ * If you only have one hunk, use ocfs2_hamming_fix_block().
+ */
+void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
+                       unsigned int fix)
+{
+        unsigned int p = calc_parity_bits(nr + d);
+        unsigned int i, b;
+
+        BUG_ON(!p);
+
+        /*
+         * If the bit to fix has an hweight of 1, it's a parity bit.  One
+         * busted parity bit is its own error.  Nothing to do here.
+         */
+        if (hweight32(fix) == 1)
+                return;
+
+        /*
+         * nr + d is the bit right past the data hunk we're looking at.
+         * If fix after that, nothing to do
+         */
+        if (fix >= calc_code_bit(nr + d))
+                return;
+
+        /*
+         * nr is the offset in the data hunk we're starting at.  Let's
+         * start b at the offset in the code buffer.  See hamming_encode()
+         * for a more detailed description of 'b'.
+         */
+        b = calc_code_bit(nr);
+        /* If the fix is before this hunk, nothing to do */
+        if (fix < b)
+                return;
+
+        for (i = 0; i < d; i++, b++)
+        {
+                /* Skip past parity bits */
+                while (hweight32(b) == 1)
+                        b++;
+
+                /*
+                 * i is the offset in this data hunk.
+                 * nr + i is the offset in the total data buffer.
+                 * b is the offset in the total code buffer.
+                 *
+                 * Thus, when b == fix, bit i in the current hunk needs
+                 * fixing.
+                 */
+                if (b == fix)
+                {
+                        if (ocfs2_test_bit(i, data))
+                                ocfs2_clear_bit(i, data);
+                        else
+                                ocfs2_set_bit(i, data);
+                        break;
+                }
+        }
+}
+
+void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
+                             unsigned int fix)
+{
+        ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
+}
+
+/*
+ * This function generates check information for a block.
+ * data is the block to be checked.  bc is a pointer to the
+ * ocfs2_block_check structure describing the crc32 and the ecc.
+ *
+ * bc should be a pointer inside data, as the function will
+ * take care of zeroing it before calculating the check information.  If
+ * bc does not point inside data, the caller must make sure any inline
+ * ocfs2_block_check structures are zeroed.
+ *
+ * The data buffer must be in on-disk endian (little endian for ocfs2).
+ * bc will be filled with little-endian values and will be ready to go to
+ * disk.
+ */
+void ocfs2_block_check_compute(void *data, size_t blocksize,
+                               struct ocfs2_block_check *bc)
+{
+        u32 crc;
+        u32 ecc;
+
+        memset(bc, 0, sizeof(struct ocfs2_block_check));
+
+        crc = crc32_le(~0, data, blocksize);
+        ecc = ocfs2_hamming_encode_block(data, blocksize);
+
+        /*
+         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
+         * larger than 16 bits.
+         */
+        BUG_ON(ecc > USHORT_MAX);
+
+        bc->bc_crc32e = cpu_to_le32(crc);
+        bc->bc_ecc = cpu_to_le16((u16)ecc);
+}
+
+/*
+ * This function validates existing check information.  Like _compute,
+ * the function will take care of zeroing bc before calculating check codes.
+ * If bc is not a pointer inside data, the caller must have zeroed any
+ * inline ocfs2_block_check structures.
+ *
+ * Again, the data passed in should be the on-disk endian.
+ */
+int ocfs2_block_check_validate(void *data, size_t blocksize,
+                               struct ocfs2_block_check *bc)
+{
+        int rc = 0;
+        struct ocfs2_block_check check;
+        u32 crc, ecc;
+
+        check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
+        check.bc_ecc = le16_to_cpu(bc->bc_ecc);
+
+        memset(bc, 0, sizeof(struct ocfs2_block_check));
+
+        /* Fast path - if the crc32 validates, we're good to go */
+        crc = crc32_le(~0, data, blocksize);
+        if (crc == check.bc_crc32e)
+                goto out;
+
+        /* Ok, try ECC fixups */
+        ecc = ocfs2_hamming_encode_block(data, blocksize);
+        ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc);
+
+        /* And check the crc32 again */
+        crc = crc32_le(~0, data, blocksize);
+        if (crc == check.bc_crc32e)
+                goto out;
+
+        rc = -EIO;
+
+out:
+        bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
+        bc->bc_ecc = cpu_to_le16(check.bc_ecc);
+
+        return rc;
+}
+
+/*
+ * This function generates check information for a list of buffer_heads.
+ * bhs is the blocks to be checked.  bc is a pointer to the
+ * ocfs2_block_check structure describing the crc32 and the ecc.
+ *
+ * bc should be a pointer inside data, as the function will
+ * take care of zeroing it before calculating the check information.  If
+ * bc does not point inside data, the caller must make sure any inline
+ * ocfs2_block_check structures are zeroed.
+ *
+ * The data buffer must be in on-disk endian (little endian for ocfs2).
+ * bc will be filled with little-endian values and will be ready to go to
+ * disk.
+ */
+void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
+                                   struct ocfs2_block_check *bc)
+{
+        int i;
+        u32 crc, ecc;
+
+        BUG_ON(nr < 0);
+
+        if (!nr)
+                return;
+
+        memset(bc, 0, sizeof(struct ocfs2_block_check));
+
+        for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
+                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
+                /*
+                 * The number of bits in a buffer is obviously b_size*8.
+                 * The offset of this buffer is b_size*i, so the bit offset
+                 * of this buffer is b_size*8*i.
+                 */
+                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
+                                                bhs[i]->b_size * 8,
+                                                bhs[i]->b_size * 8 * i);
+        }
+
+        /*
+         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
+         * larger than 16 bits.
+         */
+        BUG_ON(ecc > USHORT_MAX);
+
+        bc->bc_crc32e = cpu_to_le32(crc);
+        bc->bc_ecc = cpu_to_le16((u16)ecc);
+}
+
+/*
+ * This function validates existing check information on a list of
+ * buffer_heads.  Like _compute_bhs, the function will take care of
+ * zeroing bc before calculating check codes.  If bc is not a pointer
+ * inside data, the caller must have zeroed any inline
+ * ocfs2_block_check structures.
+ *
+ * Again, the data passed in should be the on-disk endian.
+ */
+int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
+                                   struct ocfs2_block_check *bc)
+{
+        int i, rc = 0;
+        struct ocfs2_block_check check;
+        u32 crc, ecc, fix;
+
+        BUG_ON(nr < 0);
+
+        if (!nr)
+                return 0;
+
+        check.bc_crc32e = le32_to_cpu(bc->bc_crc32e);
+        check.bc_ecc = le16_to_cpu(bc->bc_ecc);
+
+        memset(bc, 0, sizeof(struct ocfs2_block_check));
+
+        /* Fast path - if the crc32 validates, we're good to go */
+        for (i = 0, crc = ~0; i < nr; i++)
+                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
+        if (crc == check.bc_crc32e)
+                goto out;
+
+        mlog(ML_ERROR,
+             "CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
+             (unsigned int)check.bc_crc32e, (unsigned int)crc);
+
+        /* Ok, try ECC fixups */
+        for (i = 0, ecc = 0; i < nr; i++) {
+                /*
+                 * The number of bits in a buffer is obviously b_size*8.
+                 * The offset of this buffer is b_size*i, so the bit offset
+                 * of this buffer is b_size*8*i.
+                 */
+                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
+                                                bhs[i]->b_size * 8,
+                                                bhs[i]->b_size * 8 * i);
+        }
+        fix = ecc ^ check.bc_ecc;
+        for (i = 0; i < nr; i++) {
+                /*
+                 * Try the fix against each buffer.  It will only affect
+                 * one of them.
+                 */
+                ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
+                                  bhs[i]->b_size * 8 * i, fix);
+        }
+
+        /* And check the crc32 again */
+        for (i = 0, crc = ~0; i < nr; i++)
+                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
+        if (crc == check.bc_crc32e)
+                goto out;
+
+        mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
+             (unsigned int)check.bc_crc32e, (unsigned int)crc);
+
+        rc = -EIO;
+
+out:
+        bc->bc_crc32e = cpu_to_le32(check.bc_crc32e);
+        bc->bc_ecc = cpu_to_le16(check.bc_ecc);
+
+        return rc;
+}
+
+/*
+ * These are the main API.  They check the superblock flag before
+ * calling the underlying operations.
+ *
+ * They expect the buffer(s) to be in disk format.
+ */
+void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
+                            struct ocfs2_block_check *bc)
+{
+        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
+                ocfs2_block_check_compute(data, sb->s_blocksize, bc);
+}
+
+int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
+                            struct ocfs2_block_check *bc)
+{
+        int rc = 0;
+
+        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
+                rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc);
+
+        return rc;
+}
+
+void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
+                                struct buffer_head **bhs, int nr,
+                                struct ocfs2_block_check *bc)
+{
+        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
+                ocfs2_block_check_compute_bhs(bhs, nr, bc);
+}
+
+int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
+                                struct buffer_head **bhs, int nr,
+                                struct ocfs2_block_check *bc)
+{
+        int rc = 0;
+
+        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
+                rc = ocfs2_block_check_validate_bhs(bhs, nr, bc);
+
+        return rc;
+}
+