HAMMER VFS - Major retooling of the refcount mechanics, and fix a deadlock

[dragonfly.git] / sys / vfs / hammer / hammer_recover.c

/*
 * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * $DragonFly: src/sys/vfs/hammer/hammer_recover.c,v 1.29 2008/07/26 05:36:21 dillon Exp $
 */

#include "hammer.h"

static int hammer_check_tail_signature(hammer_fifo_tail_t tail,
                        hammer_off_t end_off);
static int hammer_check_head_signature(hammer_fifo_head_t head,
                        hammer_off_t beg_off);
static void hammer_recover_copy_undo(hammer_off_t undo_offset,
                        char *src, char *dst, int bytes);
static hammer_fifo_any_t hammer_recover_scan_fwd(hammer_mount_t hmp,
                        hammer_volume_t root_volume,
                        hammer_off_t *scan_offsetp,
                        int *errorp, struct hammer_buffer **bufferp);
static hammer_fifo_any_t hammer_recover_scan_rev(hammer_mount_t hmp,
                        hammer_volume_t root_volume,
                        hammer_off_t *scan_offsetp,
                        int *errorp, struct hammer_buffer **bufferp);
#if 0
static void hammer_recover_debug_dump(int w, char *buf, int bytes);
#endif
static int hammer_recover_undo(hammer_mount_t hmp, hammer_volume_t root_volume,
                        hammer_fifo_undo_t undo);

/*
 * Recover filesystem meta-data on mount.  This procedure figures out the
 * UNDO FIFO range and runs the UNDOs backwards.  The FIFO pointers are not
 * resynchronized by this procedure.
 *
 * This procedure is run near the beginning of the mount sequence, before
 * any B-Tree or high-level accesses are enabled, and is responsible for
 * restoring the meta-data to a consistent state.  High level HAMMER data
 * structures (such as the B-Tree) cannot be accessed here.
 *
 * NOTE: No information from the root volume has been cached in the
 *       hammer_mount structure yet, so we need to access the root volume's
 *       buffer directly.
 *
 * NOTE:
 */
int
hammer_recover_stage1(hammer_mount_t hmp, hammer_volume_t root_volume)
{
        hammer_blockmap_t rootmap;
        hammer_buffer_t buffer;
        hammer_off_t scan_offset;
        hammer_off_t scan_offset_save;
        hammer_off_t bytes;
        hammer_fifo_any_t head;
        hammer_off_t first_offset;
        hammer_off_t last_offset;
        u_int32_t seqno;
        int error;

        /*
         * Examine the UNDO FIFO indices in the volume header.
         */
        rootmap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
        first_offset = rootmap->first_offset;
        last_offset  = rootmap->next_offset;
        buffer = NULL;
        error = 0;

        if (first_offset > rootmap->alloc_offset ||
            last_offset > rootmap->alloc_offset) {
                kprintf("HAMMER(%s) Illegal UNDO FIFO index range "
                        "%016jx, %016jx limit %016jx\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)first_offset,
                        (intmax_t)last_offset,
                        (intmax_t)rootmap->alloc_offset);
                error = EIO;
                goto done;
        }

        /*
         * In HAMMER version 4+ filesystems the volume header does NOT
         * contain definitive UNDO FIFO state.  In particular, the
         * rootmap->next_offset may not be indexed completely to the
         * end of the active UNDO FIFO.
         */
        if (hmp->version >= HAMMER_VOL_VERSION_FOUR) {
                /*
                 * To find the definitive range we must first scan backwards
                 * from first_offset to locate the first real record and
                 * extract the sequence number from it.  This record is not
                 * part of the active undo space.
                 */
                scan_offset = first_offset;
                seqno = 0;

                for (;;) {
                        head = hammer_recover_scan_rev(hmp, root_volume,
                                                       &scan_offset,
                                                       &error, &buffer);
                        if (error)
                                break;
                        if (head->head.hdr_type != HAMMER_HEAD_TYPE_PAD) {
                                seqno = head->head.hdr_seq;
                                break;
                        }
                }
                if (error) {
                        kprintf("HAMMER(%s) meta-data recovery failure "
                                "during seqno backscan\n",
                                root_volume->ondisk->vol_name);
                        goto done;
                }

                /*
                 * Scan forwards from first_offset and (seqno+1) looking
                 * for a sequence space discontinuity.  This denotes the
                 * end of the active FIFO area.
                 *
                 * NOTE: For the case where the FIFO is empty the very first
                 *       record we find will be discontinuous.
                 *
                 * NOTE: Do not include trailing PADs in the scan range,
                 *       and remember the returned scan_offset after a
                 *       fwd iteration points to the end of the returned
                 *       record.
                 */
                kprintf("HAMMER(%s) meta-data recovery check seqno=%08x\n",
                        root_volume->ondisk->vol_name,
                        seqno);

                scan_offset = first_offset;
                scan_offset_save = scan_offset;
                ++seqno;
                for (;;) {
                        head = hammer_recover_scan_fwd(hmp, root_volume,
                                                       &scan_offset,
                                                       &error, &buffer);
                        if (error)
                                break;
                        if (head->head.hdr_type != HAMMER_HEAD_TYPE_PAD) {
                                if (seqno != head->head.hdr_seq) {
                                        scan_offset = scan_offset_save;
                                        break;
                                }
                                scan_offset_save = scan_offset;
                                ++seqno;
                        }

#if 0
                        /*
                         * If the forward scan is grossly ahead of last_offset
                         * then something is wrong.  last_offset is supposed
                         * to be flushed out
                         */
                        if (last_offset >= scan_offset) {
                                bytes = last_offset - scan_offset;
                        } else {
                                bytes = rootmap->alloc_offset - scan_offset +
                                        (last_offset & HAMMER_OFF_LONG_MASK);
                        }
                        if (bytes >
                            (rootmap->alloc_offset & HAMMER_OFF_LONG_MASK) *
                            4 / 5) {
                                kprintf("HAMMER(%s) meta-data forward scan is "
                                        "grossly beyond the last_offset in "
                                        "the volume header, this can't be "
                                        "right.\n",
                                        root_volume->ondisk->vol_name);
                                error = EIO;
                                break;
                        }
#endif
                }

                /*
                 * Store the seqno.  This will be the next seqno we lay down
                 * when generating new UNDOs.
                 */
                hmp->undo_seqno = seqno;
                if (error) {
                        kprintf("HAMMER(%s) meta-data recovery failure "
                                "during seqno fwdscan\n",
                                root_volume->ondisk->vol_name);
                        goto done;
                }
                last_offset = scan_offset;
                kprintf("HAMMER(%s) meta-data recovery range %016jx-%016jx "
                        "(invol %016jx) endseqno=%08x\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)first_offset,
                        (intmax_t)last_offset,
                        (intmax_t)rootmap->next_offset,
                        seqno);
        }

        /*
         * Calculate the size of the active portion of the FIFO.  If the
         * FIFO is empty the filesystem is clean and no further action is
         * needed.
         */
        if (last_offset >= first_offset) {
                bytes = last_offset - first_offset;
        } else {
                bytes = rootmap->alloc_offset - first_offset +
                        (last_offset & HAMMER_OFF_LONG_MASK);
        }
        if (bytes == 0) {
                error = 0;
                goto done;
        }

        kprintf("HAMMER(%s) Start meta-data recovery %016jx - %016jx "
                "(%jd bytes of UNDO)%s\n",
                root_volume->ondisk->vol_name,
                (intmax_t)first_offset,
                (intmax_t)last_offset,
                (intmax_t)bytes,
                (hmp->ronly ? " (RO)" : "(RW)"));
        if (bytes > (rootmap->alloc_offset & HAMMER_OFF_LONG_MASK)) {
                kprintf("Undo size is absurd, unable to mount\n");
                error = EIO;
                goto done;
        }

        /*
         * Scan the UNDOs backwards.
         */
        scan_offset = last_offset;

        while ((int64_t)bytes > 0) {
                KKASSERT(scan_offset != first_offset);
                head = hammer_recover_scan_rev(hmp, root_volume,
                                               &scan_offset, &error, &buffer);
                if (error)
                        break;
                error = hammer_recover_undo(hmp, root_volume, &head->undo);
                if (error) {
                        kprintf("HAMMER(%s) UNDO record at %016jx failed\n",
                                root_volume->ondisk->vol_name,
                                (intmax_t)scan_offset - head->head.hdr_size);
                        break;
                }
                bytes -= head->head.hdr_size;

                /*
                 * If too many dirty buffers have built up we have to flush'm
                 * out.  As long as we do not flush out the volume header
                 * a crash here should not cause any problems.
                 *
                 * buffer must be released so the flush can assert that
                 * all buffers are idle.
                 */
                if (hammer_flusher_meta_limit(hmp)) {
                        if (buffer) {
                                hammer_rel_buffer(buffer, 0);
                                buffer = NULL;
                        }
                        if (hmp->ronly == 0) {
                                hammer_recover_flush_buffers(hmp, root_volume,
                                                             0);
                                kprintf("HAMMER(%s) Continuing recovery\n",
                                        root_volume->ondisk->vol_name);
                        } else {
                                kprintf("HAMMER(%s) Recovery failure: Insufficient buffer cache to hold dirty buffers on read-only mount!\n",
                                        root_volume->ondisk->vol_name);
                                error = EIO;
                                break;
                        }
                }
        }
done:
        if (buffer) {
                hammer_rel_buffer(buffer, 0);
                buffer = NULL;
        }

        /*
         * After completely flushing all the recovered buffers the volume
         * header will also be flushed.
         */
        if (root_volume->io.recovered == 0) {
                hammer_ref_volume(root_volume);
                root_volume->io.recovered = 1;
        }

        /*
         * Finish up flushing (or discarding) recovered buffers.  FIFO
         * indices in the volume header are updated to the actual undo
         * range but will not be collapsed until stage 2.
         */
        if (error == 0) {
                hammer_modify_volume(NULL, root_volume, NULL, 0);
                rootmap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
                rootmap->first_offset = first_offset;
                rootmap->next_offset = last_offset;
                hammer_modify_volume_done(root_volume);
                if (hmp->ronly == 0)
                        hammer_recover_flush_buffers(hmp, root_volume, 1);
        } else {
                hammer_recover_flush_buffers(hmp, root_volume, -1);
        }
        kprintf("HAMMER(%s) End meta-data recovery\n",
                root_volume->ondisk->vol_name);
        return (error);
}

/*
 * Execute redo operations
 *
 * This procedure is run at the end of the mount sequence, after the hammer
 * mount structure has been completely initialized but before the filesystem
 * goes live.  It can access standard cursors, the B-Tree, flush the
 * filesystem, and so forth.
 *
 * This code may only be called for read-write mounts or when a mount
 * switches from read-only to read-write.
 *
 * The stage1 code will have already calculated the correct FIFO range
 * and stored it in the rootmap.
 */
int
hammer_recover_stage2(hammer_mount_t hmp, hammer_volume_t root_volume)
{
        hammer_blockmap_t rootmap;
        hammer_buffer_t buffer;
        hammer_off_t scan_offset;
        hammer_off_t bytes;
        hammer_fifo_any_t head;
        hammer_off_t first_offset;
        hammer_off_t last_offset;
        int error;

        /*
         * Stage 2 can only be run on a RW mount, or when the mount is
         * switched from RO to RW.  It must be run only once.
         */
        KKASSERT(hmp->ronly == 0);

        if (hmp->hflags & HMNT_STAGE2)
                return(0);
        hmp->hflags |= HMNT_STAGE2;

        /*
         * Examine the UNDO FIFO.  If it is empty the filesystem is clean
         * and no action need be taken.
         */
        rootmap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
        first_offset = rootmap->first_offset;
        last_offset  = rootmap->next_offset;
        if (first_offset == last_offset)
                return(0);

        if (last_offset >= first_offset) {
                bytes = last_offset - first_offset;
        } else {
                bytes = rootmap->alloc_offset - first_offset +
                        (last_offset & HAMMER_OFF_LONG_MASK);
        }
        kprintf("HAMMER(%s) Start redo recovery %016jx - %016jx "
                "(%jd bytes of UNDO)%s\n",
                root_volume->ondisk->vol_name,
                (intmax_t)first_offset,
                (intmax_t)last_offset,
                (intmax_t)bytes,
                (hmp->ronly ? " (RO)" : "(RW)"));
        if (bytes > (rootmap->alloc_offset & HAMMER_OFF_LONG_MASK)) {
                kprintf("Undo size is absurd, unable to mount\n");
                return(EIO);
        }

        /*
         * Scan the REDOs forwards.
         */
        scan_offset = first_offset;
        buffer = NULL;

        while (bytes) {
                KKASSERT(scan_offset != last_offset);

                head = hammer_recover_scan_fwd(hmp, root_volume,
                                               &scan_offset, &error, &buffer);
                if (error)
                        break;

#if 0
                error = hammer_recover_redo(hmp, root_volume, &head->redo);
#endif
                if (error) {
                        kprintf("HAMMER(%s) UNDO record at %016jx failed\n",
                                root_volume->ondisk->vol_name,
                                (intmax_t)scan_offset - head->head.hdr_size);
                        break;
                }
                bytes -= head->head.hdr_size;
        }
        if (buffer) {
                hammer_rel_buffer(buffer, 0);
                buffer = NULL;
        }

        /*
         * Finish up flushing (or discarding) recovered buffers by executing
         * a normal flush cycle.  Setting HMNT_UNDO_DIRTY bypasses degenerate
         * case tests and forces the flush in order to update the FIFO indices.
         *
         * If a crash occurs during the flush the entire undo/redo will be
         * re-run during recovery on the next mount.
         */
        if (error == 0) {
                if (rootmap->first_offset != rootmap->next_offset)
                        hmp->hflags |= HMNT_UNDO_DIRTY;
                hammer_flusher_sync(hmp);
        }
        kprintf("HAMMER(%s) End redo recovery\n",
                root_volume->ondisk->vol_name);
        return (error);
}

/*
 * Scan backwards from *scan_offsetp, return the FIFO record prior to the
 * record at *scan_offsetp or NULL if an error occured.
 *
 * On return *scan_offsetp will be the offset of the returned record.
 */
hammer_fifo_any_t
hammer_recover_scan_rev(hammer_mount_t hmp, hammer_volume_t root_volume,
                        hammer_off_t *scan_offsetp,
                        int *errorp, struct hammer_buffer **bufferp)
{
        hammer_off_t scan_offset;
        hammer_blockmap_t rootmap;
        hammer_fifo_any_t head;
        hammer_fifo_tail_t tail;

        rootmap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
        scan_offset = *scan_offsetp;

        if (hammer_debug_general & 0x0080)
                kprintf("rev scan_offset %016jx\n", (intmax_t)scan_offset);
        if (scan_offset == HAMMER_ZONE_ENCODE(HAMMER_ZONE_UNDO_INDEX, 0))
                scan_offset = rootmap->alloc_offset;
        if (scan_offset - sizeof(*tail) <
            HAMMER_ZONE_ENCODE(HAMMER_ZONE_UNDO_INDEX, 0)) {
                kprintf("HAMMER(%s) UNDO record at %016jx FIFO underflow\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)scan_offset);
                *errorp = EIO;
                return (NULL);
        }
        tail = hammer_bread(hmp, scan_offset - sizeof(*tail),
                            errorp, bufferp);
        if (*errorp) {
                kprintf("HAMMER(%s) Unable to read UNDO TAIL "
                        "at %016jx\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)scan_offset - sizeof(*tail));
                return (NULL);
        }

        if (hammer_check_tail_signature(tail, scan_offset) != 0) {
                kprintf("HAMMER(%s) Illegal UNDO TAIL signature "
                        "at %016jx\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)scan_offset - sizeof(*tail));
                *errorp = EIO;
                return (NULL);
        }
        head = (void *)((char *)tail + sizeof(*tail) - tail->tail_size);
        *scan_offsetp = scan_offset - head->head.hdr_size;

        return (head);
}

/*
 * Scan forwards from *scan_offsetp, return the FIFO record or NULL if
 * an error occured.
 *
 * On return *scan_offsetp will be the offset of the record following
 * the returned record.
 */
hammer_fifo_any_t
hammer_recover_scan_fwd(hammer_mount_t hmp, hammer_volume_t root_volume,
                        hammer_off_t *scan_offsetp,
                        int *errorp, struct hammer_buffer **bufferp)
{
        hammer_off_t scan_offset;
        hammer_blockmap_t rootmap;
        hammer_fifo_any_t head;

        rootmap = &root_volume->ondisk->vol0_blockmap[HAMMER_ZONE_UNDO_INDEX];
        scan_offset = *scan_offsetp;

        if (hammer_debug_general & 0x0080)
                kprintf("fwd scan_offset %016jx\n", (intmax_t)scan_offset);
        if (scan_offset == rootmap->alloc_offset)
                scan_offset = HAMMER_ZONE_ENCODE(HAMMER_ZONE_UNDO_INDEX, 0);

        head = hammer_bread(hmp, scan_offset, errorp, bufferp);
        if (*errorp) {
                kprintf("HAMMER(%s) Unable to read UNDO HEAD at %016jx\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)scan_offset);
                return (NULL);
        }

        if (hammer_check_head_signature(&head->head, scan_offset) != 0) {
                kprintf("HAMMER(%s) Illegal UNDO TAIL signature "
                        "at %016jx\n",
                        root_volume->ondisk->vol_name,
                        (intmax_t)scan_offset);
                *errorp = EIO;
                return (NULL);
        }
        scan_offset += head->head.hdr_size;
        if (scan_offset == rootmap->alloc_offset)
                scan_offset = HAMMER_ZONE_ENCODE(HAMMER_ZONE_UNDO_INDEX, 0);
        *scan_offsetp = scan_offset;

        return (head);
}

/*
 * Helper function for hammer_check_{head,tail}_signature().  Check stuff
 * once the head and tail has been established.
 *
 * This function validates the entire FIFO record wrapper.
 */
static __inline
int
_hammer_check_signature(hammer_fifo_head_t head, hammer_fifo_tail_t tail,
                        hammer_off_t beg_off)
{
        hammer_off_t end_off;
        u_int32_t crc;
        int bytes;

        /*
         * Check signatures.  The tail signature is allowed to be the
         * head signature only for 8-byte PADs.
         */
        if (head->hdr_signature != HAMMER_HEAD_SIGNATURE) {
                kprintf("HAMMER: FIFO record bad head signature "
                        "%04x at %016jx\n",
                        head->hdr_signature,
                        (intmax_t)beg_off);
                return(2);
        }
        if (head->hdr_size < HAMMER_HEAD_ALIGN ||
            (head->hdr_size & HAMMER_HEAD_ALIGN_MASK)) {
                kprintf("HAMMER: FIFO record unaligned or bad size"
                        "%04x at %016jx\n",
                        head->hdr_size,
                        (intmax_t)beg_off);
                return(2);
        }
        end_off = beg_off + head->hdr_size;

        if (head->hdr_type != HAMMER_HEAD_TYPE_PAD ||
            (size_t)(end_off - beg_off) != sizeof(*tail)) {
                if (head->hdr_type != tail->tail_type) {
                        kprintf("HAMMER: FIFO record head/tail type mismatch "
                                "%04x %04x at %016jx\n",
                                head->hdr_type, tail->tail_type,
                                (intmax_t)beg_off);
                        return(2);
                }
                if (head->hdr_size != tail->tail_size) {
                        kprintf("HAMMER: FIFO record head/tail size mismatch "
                                "%04x %04x at %016jx\n",
                                head->hdr_size, tail->tail_size,
                                (intmax_t)beg_off);
                        return(2);
                }
                if (tail->tail_signature != HAMMER_TAIL_SIGNATURE) {
                        kprintf("HAMMER: FIFO record bad tail signature "
                                "%04x at %016jx\n",
                                tail->tail_signature,
                                (intmax_t)beg_off);
                        return(3);
                }
        }

        /*
         * Non-PAD records must have a CRC and must be sized at
         * least large enough to fit the head and tail.
         */
        if (head->hdr_type != HAMMER_HEAD_TYPE_PAD) {
                crc = crc32(head, HAMMER_FIFO_HEAD_CRCOFF) ^
                      crc32(head + 1, head->hdr_size - sizeof(*head));
                if (head->hdr_crc != crc) {
                        kprintf("HAMMER: FIFO record CRC failed %08x %08x "
                                "at %016jx\n",
                                head->hdr_crc, crc,
                                (intmax_t)beg_off);
                        return(EIO);
                }
                if (head->hdr_size < sizeof(*head) + sizeof(*tail)) {
                        kprintf("HAMMER: FIFO record too small "
                                "%04x at %016jx\n",
                                head->hdr_size,
                                (intmax_t)beg_off);
                        return(EIO);
                }
        }

        /*
         * Check the tail
         */
        bytes = head->hdr_size;
        tail = (void *)((char *)head + bytes - sizeof(*tail));
        if (tail->tail_size != head->hdr_size) {
                kprintf("HAMMER: Bad tail size %04x vs %04x at %016jx\n",
                        tail->tail_size, head->hdr_size,
                        (intmax_t)beg_off);
                return(EIO);
        }
        if (tail->tail_type != head->hdr_type) {
                kprintf("HAMMER: Bad tail type %04x vs %04x at %016jx\n",
                        tail->tail_type, head->hdr_type,
                        (intmax_t)beg_off);
                return(EIO);
        }

        return(0);
}

/*
 * Check that the FIFO record is in-bounds given the head and the
 * hammer offset.
 *
 * Also checks that the head and tail structures agree with each other,
 * but does not check beyond the signature, type, and size.
 */
static int
hammer_check_head_signature(hammer_fifo_head_t head, hammer_off_t beg_off)
{
        hammer_fifo_tail_t tail;
        hammer_off_t end_off;

        /*
         * head overlaps buffer boundary.  This could be a PAD so only
         * check the minimum PAD size here.
         */
        if (((beg_off + sizeof(*tail) - 1) ^ (beg_off)) & ~HAMMER_BUFMASK64)
                return(1);

        /*
         * Calculate the ending offset and make sure the record does
         * not cross a buffer boundary.
         */
        end_off = beg_off + head->hdr_size;
        if ((beg_off ^ (end_off - 1)) & ~HAMMER_BUFMASK64)
                return(1);
        tail = (void *)((char *)head + head->hdr_size - sizeof(*tail));
        return (_hammer_check_signature(head, tail, beg_off));
}

/*
 * Check that the FIFO record is in-bounds given the tail and the
 * hammer offset.  The offset is pointing at the ending boundary of the
 * record.
 *
 * Also checks that the head and tail structures agree with each other,
 * but does not check beyond the signature, type, and size.
 */
static int
hammer_check_tail_signature(hammer_fifo_tail_t tail, hammer_off_t end_off)
{
        hammer_fifo_head_t head;
        hammer_off_t beg_off;

        /*
         * tail overlaps buffer boundary
         */
        if (((end_off - sizeof(*tail)) ^ (end_off - 1)) & ~HAMMER_BUFMASK64)
                return(1);

        /*
         * Calculate the begining offset and make sure the record does
         * not cross a buffer boundary.
         */
        beg_off = end_off - tail->tail_size;
        if ((beg_off ^ (end_off - 1)) & ~HAMMER_BUFMASK64)
                return(1);
        head = (void *)((char *)tail + sizeof(*tail) - tail->tail_size);
        return (_hammer_check_signature(head, tail, beg_off));
}

static int
hammer_recover_undo(hammer_mount_t hmp, hammer_volume_t root_volume,
                    hammer_fifo_undo_t undo)
{
        hammer_volume_t volume;
        hammer_buffer_t buffer;
        hammer_off_t buf_offset;
        int zone;
        int error;
        int vol_no;
        int bytes;
        u_int32_t offset;

        /*
         * Only process UNDO records.  Flag if we find other records to
         * optimize stage2 recovery.
         */
        if (undo->head.hdr_type != HAMMER_HEAD_TYPE_UNDO) {
                if (undo->head.hdr_type == HAMMER_HEAD_TYPE_REDO)
                        hmp->hflags |= HMNT_HASREDO;
                return(0);
        }

        /*
         * Validate the UNDO record.
         */
        bytes = undo->head.hdr_size - sizeof(*undo) -
                sizeof(struct hammer_fifo_tail);
        if (bytes < 0 || undo->undo_data_bytes < 0 ||
            undo->undo_data_bytes > bytes) {
                kprintf("HAMMER: Corrupt UNDO record, undo_data_bytes %d/%d\n",
                        undo->undo_data_bytes, bytes);
                return(EIO);
        }

        bytes = undo->undo_data_bytes;

        /*
         * The undo offset may only be a zone-1 or zone-2 offset.
         *
         * Currently we only support a zone-1 offset representing the
         * volume header.
         */
        zone = HAMMER_ZONE_DECODE(undo->undo_offset);
        offset = undo->undo_offset & HAMMER_BUFMASK;

        if (offset + bytes > HAMMER_BUFSIZE) {
                kprintf("HAMMER: Corrupt UNDO record, bad offset\n");
                return (EIO);
        }

        switch(zone) {
        case HAMMER_ZONE_RAW_VOLUME_INDEX:
                vol_no = HAMMER_VOL_DECODE(undo->undo_offset);
                volume = hammer_get_volume(hmp, vol_no, &error);
                if (volume == NULL) {
                        kprintf("HAMMER: UNDO record, "
                                "cannot access volume %d\n", vol_no);
                        break;
                }
                hammer_modify_volume(NULL, volume, NULL, 0);
                hammer_recover_copy_undo(undo->undo_offset,
                                         (char *)(undo + 1),
                                         (char *)volume->ondisk + offset,
                                         bytes);
                hammer_modify_volume_done(volume);

                /*
                 * Multiple modifications may be made to the same buffer.
                 * Also, the volume header cannot be written out until
                 * everything else has been flushed.  This also
                 * covers the read-only case by preventing the kernel from
                 * flushing the buffer.
                 */
                if (volume->io.recovered == 0)
                        volume->io.recovered = 1;
                else
                        hammer_rel_volume(volume, 0);
                break;
        case HAMMER_ZONE_RAW_BUFFER_INDEX:
                buf_offset = undo->undo_offset & ~HAMMER_BUFMASK64;
                buffer = hammer_get_buffer(hmp, buf_offset, HAMMER_BUFSIZE,
                                           0, &error);
                if (buffer == NULL) {
                        kprintf("HAMMER: UNDO record, "
                                "cannot access buffer %016jx\n",
                                (intmax_t)undo->undo_offset);
                        break;
                }
                hammer_modify_buffer(NULL, buffer, NULL, 0);
                hammer_recover_copy_undo(undo->undo_offset,
                                         (char *)(undo + 1),
                                         (char *)buffer->ondisk + offset,
                                         bytes);
                hammer_modify_buffer_done(buffer);

                /*
                 * Multiple modifications may be made to the same buffer,
                 * improve performance by delaying the flush.  This also
                 * covers the read-only case by preventing the kernel from
                 * flushing the buffer.
                 */
                if (buffer->io.recovered == 0)
                        buffer->io.recovered = 1;
                else
                        hammer_rel_buffer(buffer, 0);
                break;
        default:
                kprintf("HAMMER: Corrupt UNDO record\n");
                error = EIO;
        }
        return (error);
}

static void
hammer_recover_copy_undo(hammer_off_t undo_offset, 
                         char *src, char *dst, int bytes)
{
        if (hammer_debug_general & 0x0080) {
                kprintf("UNDO %016jx: %d\n",
                        (intmax_t)undo_offset, bytes);
        }
#if 0
        kprintf("UNDO %016jx:", (intmax_t)undo_offset);
        hammer_recover_debug_dump(22, dst, bytes);
        kprintf("%22s", "to:");
        hammer_recover_debug_dump(22, src, bytes);
#endif
        bcopy(src, dst, bytes);
}

#if 0

static void
hammer_recover_debug_dump(int w, char *buf, int bytes)
{
        int i;

        for (i = 0; i < bytes; ++i) {
                if (i && (i & 15) == 0)
                        kprintf("\n%*.*s", w, w, "");
                kprintf(" %02x", (unsigned char)buf[i]);
        }
        kprintf("\n");
}

#endif

/*
 * Flush recovered buffers from recovery operations.  The call to this
 * routine may be delayed if a read-only mount was made and then later
 * upgraded to read-write.  This routine is also called when unmounting
 * a read-only mount to clean out recovered (dirty) buffers which we
 * couldn't flush (because the mount is read-only).
 *
 * The volume header is always written last.  The UNDO FIFO will be forced
 * to zero-length by setting next_offset to first_offset.  This leaves the
 * (now stale) UNDO information used to recover the disk available for
 * forensic analysis.
 *
 * final is typically 0 or 1.  The volume header is only written if final
 * is 1.  If final is -1 the recovered buffers are discarded instead of
 * written and root_volume can also be passed as NULL in that case.
 */
static int hammer_recover_flush_volume_callback(hammer_volume_t, void *);
static int hammer_recover_flush_buffer_callback(hammer_buffer_t, void *);

void
hammer_recover_flush_buffers(hammer_mount_t hmp, hammer_volume_t root_volume,
                             int final)
{
        /*
         * Flush the buffers out asynchronously, wait for all the I/O to
         * complete, then do it again to destroy the buffer cache buffer
         * so it doesn't alias something later on.
         */
        RB_SCAN(hammer_buf_rb_tree, &hmp->rb_bufs_root, NULL,
                hammer_recover_flush_buffer_callback, &final);
        hammer_io_wait_all(hmp, "hmrrcw", 1);
        RB_SCAN(hammer_buf_rb_tree, &hmp->rb_bufs_root, NULL,
                hammer_recover_flush_buffer_callback, &final);

        /*
         * Flush all volume headers except the root volume.  If final < 0
         * we discard all volume headers including the root volume.
         */
        if (final >= 0) {
                RB_SCAN(hammer_vol_rb_tree, &hmp->rb_vols_root, NULL,
                        hammer_recover_flush_volume_callback, root_volume);
        } else {
                RB_SCAN(hammer_vol_rb_tree, &hmp->rb_vols_root, NULL,
                        hammer_recover_flush_volume_callback, NULL);
        }

        /*
         * Finalize the root volume header.
         */
        if (root_volume && root_volume->io.recovered && final > 0) {
                hammer_io_wait_all(hmp, "hmrflx", 1);
                root_volume->io.recovered = 0;
                hammer_io_flush(&root_volume->io, 0);
                hammer_rel_volume(root_volume, 0);
                hammer_io_wait_all(hmp, "hmrfly", 1);
        }
}

/*
 * Callback to flush volume headers.  If discarding data will be NULL and
 * all volume headers (including the root volume) will be discarded.
 * Otherwise data is the root_volume and we flush all volume headers
 * EXCEPT the root_volume.
 *
 * Clear any I/O error or modified condition when discarding buffers to
 * clean up the reference count, otherwise the buffer may have extra refs
 * on it.
 */
static
int
hammer_recover_flush_volume_callback(hammer_volume_t volume, void *data)
{
        hammer_volume_t root_volume = data;

        if (volume->io.recovered && volume != root_volume) {
                volume->io.recovered = 0;
                if (root_volume != NULL) {
                        hammer_io_flush(&volume->io, 0);
                } else {
                        hammer_io_clear_error(&volume->io);
                        hammer_io_clear_modify(&volume->io, 1);
                }
                hammer_rel_volume(volume, 0);
        }
        return(0);
}

/*
 * Flush or discard recovered I/O buffers.
 *
 * Clear any I/O error or modified condition when discarding buffers to
 * clean up the reference count, otherwise the buffer may have extra refs
 * on it.
 */
static
int
hammer_recover_flush_buffer_callback(hammer_buffer_t buffer, void *data)
{
        int final = *(int *)data;
        int flush;

        if (buffer->io.recovered) {
                buffer->io.recovered = 0;
                buffer->io.reclaim = 1;
                if (final < 0) {
                        hammer_io_clear_error(&buffer->io);
                        hammer_io_clear_modify(&buffer->io, 1);
                } else {
                        hammer_io_flush(&buffer->io, 0);
                }
                hammer_rel_buffer(buffer, 0);
        } else {
                flush = hammer_ref_interlock(&buffer->io.lock);
                if (flush)
                        ++hammer_count_refedbufs;

                if (final < 0) {
                        hammer_io_clear_error(&buffer->io);
                        hammer_io_clear_modify(&buffer->io, 1);
                }
                KKASSERT(hammer_oneref(&buffer->io.lock));
                buffer->io.reclaim = 1;
                hammer_rel_buffer(buffer, flush);
        }
        return(0);
}