sbin/hammer: Use big-block append offset to limit recovery scan range

[dragonfly.git] / sbin / hammer / cmd_recover.c

/*
 * Copyright (c) 2010 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.
 */

#include "hammer.h"

struct recover_dict {
        struct recover_dict *next;
        struct recover_dict *parent;
        int64_t obj_id;
        uint8_t obj_type;
        uint8_t flags;
        uint16_t pfs_id;
        int64_t size;
        char    *name;
};

#define DICTF_MADEDIR   0x01
#define DICTF_MADEFILE  0x02
#define DICTF_PARENT    0x04    /* parent attached for real */
#define DICTF_TRAVERSED 0x80

typedef struct bigblock *bigblock_t;

static void recover_top(char *ptr, hammer_off_t offset);
static void recover_elm(hammer_btree_leaf_elm_t leaf);
static struct recover_dict *get_dict(int64_t obj_id, uint16_t pfs_id);
static char *recover_path(struct recover_dict *dict);
static void sanitize_string(char *str);
static hammer_off_t scan_raw_limit(void);
static void scan_bigblocks(int target_zone);
static void free_bigblocks(void);
static void add_bigblock_entry(hammer_off_t offset,
        hammer_blockmap_layer1_t layer1, hammer_blockmap_layer2_t layer2);
static bigblock_t get_bigblock_entry(hammer_off_t offset);

static const char *TargetDir;
static int CachedFd = -1;
static char *CachedPath;

typedef struct bigblock {
        RB_ENTRY(bigblock) entry;
        hammer_off_t phys_offset; /* zone-2 */
        struct hammer_blockmap_layer1 layer1;
        struct hammer_blockmap_layer2 layer2;
} *bigblock_t;

static int
bigblock_cmp(bigblock_t b1, bigblock_t b2)
{
        if (b1->phys_offset < b2->phys_offset)
                return(-1);
        if (b1->phys_offset > b2->phys_offset)
                return(1);
        return(0);
}

RB_HEAD(bigblock_rb_tree, bigblock) ZoneTree = RB_INITIALIZER(&ZoneTree);
RB_PROTOTYPE2(bigblock_rb_tree, bigblock, entry, bigblock_cmp, hammer_off_t);
RB_GENERATE2(bigblock_rb_tree, bigblock, entry, bigblock_cmp, hammer_off_t,
        phys_offset);

/*
 * There was a hidden bug here while iterating zone-2 offset as
 * shown in an example below.
 *
 * If a volume was once used as HAMMER filesystem which consists of
 * multiple volumes whose usage has reached beyond the first volume,
 * and then later re-formatted only using 1 volume, hammer recover is
 * likely to hit assertion in get_buffer() due to having access to
 * invalid volume (vol1,2,...) from old filesystem data.
 *
 * To avoid this, now the command only scans upto the last big-block
 * that's actually used for filesystem data or meta-data at the moment,
 * if all layer1/2 entries have correct CRC values. This also avoids
 * recovery of irrelevant files from old filesystem.
 *
 * It also doesn't scan beyond append offset of big-blocks in B-Tree
 * zone to avoid recovery of irrelevant files from old filesystem,
 * if layer1/2 entries for those big-blocks have correct CRC values.
 *
 * |-----vol0-----|-----vol1-----|-----vol2-----| old filesystem
 * <-----------------------> used by old filesystem
 *
 * |-----vol0-----| new filesystem
 * <-----> used by new filesystem
 *        <-------> unused, invalid data from old filesystem
 *              <-> B-Tree nodes likely to point to vol1
 */

void
hammer_cmd_recover(char **av, int ac)
{
        struct buffer_info *data_buffer;
        struct volume_info *volume;
        bigblock_t b = NULL;
        hammer_off_t off;
        hammer_off_t off_end;
        hammer_off_t off_blk;
        hammer_off_t raw_limit = 0;
        hammer_off_t zone_limit = 0;
        char *ptr;
        int i;
        int target_zone = HAMMER_ZONE_BTREE_INDEX;
        int full = 0;
        int quick = 0;

        if (ac < 1) {
                fprintf(stderr, "hammer recover <target_dir> [full|quick]\n");
                exit(1);
        }

        TargetDir = av[0];
        if (ac > 1) {
                if (!strcmp(av[1], "full"))
                        full = 1;
                if (!strcmp(av[1], "quick"))
                        quick = 1;
        }
        assert(!full || !quick);

        if (mkdir(TargetDir, 0777) == -1) {
                if (errno != EEXIST) {
                        perror("mkdir");
                        exit(1);
                }
        }

        printf("Running %sraw scan of HAMMER image, recovering to %s\n",
                full ? "full " : quick ? "quick " : "",
                TargetDir);

        if (!full) {
                scan_bigblocks(target_zone);
                raw_limit = scan_raw_limit();
                if (raw_limit) {
                        raw_limit += HAMMER_BIGBLOCK_SIZE;
                        assert(hammer_is_zone_raw_buffer(raw_limit));
                }
        }

        if (quick) {
                assert(!full);
                if (!RB_EMPTY(&ZoneTree)) {
                        printf("Found zone-%d big-blocks at\n", target_zone);
                        RB_FOREACH(b, bigblock_rb_tree, &ZoneTree)
                                printf("%016jx\n", b->phys_offset);

                        b = RB_MAX(bigblock_rb_tree, &ZoneTree);
                        zone_limit = b->phys_offset + HAMMER_BIGBLOCK_SIZE;
                        assert(hammer_is_zone_raw_buffer(zone_limit));
                }
        }

        if (raw_limit || zone_limit) {
#define _fmt "Scanning zone-%d big-blocks till %016jx"
                if (!raw_limit) /* unlikely */
                        printf(_fmt" ???", target_zone, zone_limit);
                else if (!zone_limit)
                        printf(_fmt, HAMMER_ZONE_RAW_BUFFER_INDEX, raw_limit);
                else if (raw_limit >= zone_limit)
                        printf(_fmt, target_zone, zone_limit);
                else /* unlikely */
                        printf(_fmt" ???", HAMMER_ZONE_RAW_BUFFER_INDEX, raw_limit);
                printf("\n");
        }

        data_buffer = NULL;
        for (i = 0; i < HAMMER_MAX_VOLUMES; i++) {
                volume = get_volume(i);
                if (volume == NULL)
                        continue;

                printf("Scanning volume %d size %s\n",
                        volume->vol_no, sizetostr(volume->size));
                off = HAMMER_ENCODE_RAW_BUFFER(volume->vol_no, 0);
                off_end = off + HAMMER_VOL_BUF_SIZE(volume->ondisk);

                while (off < off_end) {
                        off_blk = off & HAMMER_BIGBLOCK_MASK64;
                        if (off_blk == 0)
                                b = get_bigblock_entry(off);

                        if (raw_limit) {
                                if (off >= raw_limit) {
                                        printf("Done %016jx\n", (uintmax_t)off);
                                        goto end;
                                }
                        }
                        if (zone_limit) {
                                if (off >= zone_limit) {
                                        printf("Done %016jx\n", (uintmax_t)off);
                                        goto end;
                                }
                                if (b == NULL) {
                                        off = HAMMER_ZONE_LAYER2_NEXT_OFFSET(off);
                                        continue;
                                }
                        }

                        if (b) {
                                if (hammer_crc_test_layer1(&b->layer1) &&
                                    hammer_crc_test_layer2(&b->layer2) &&
                                    off_blk >= b->layer2.append_off) {
                                        off = HAMMER_ZONE_LAYER2_NEXT_OFFSET(off);
                                        continue;
                                }
                        }

                        ptr = get_buffer_data(off, &data_buffer, 0);
                        if (ptr)
                                recover_top(ptr, off);
                        off += HAMMER_BUFSIZE;
                }
        }
end:
        rel_buffer(data_buffer);
        free_bigblocks();

        if (CachedPath) {
                free(CachedPath);
                close(CachedFd);
                CachedPath = NULL;
                CachedFd = -1;
        }
}

static __inline
void
print_node(hammer_node_ondisk_t node, hammer_off_t offset)
{
        char buf[HAMMER_BTREE_LEAF_ELMS + 1];
        int maxcount = hammer_node_max_elements(node->type);
        int i;

        for (i = 0; i < node->count && i < maxcount; ++i)
                buf[i] = hammer_elm_btype(&node->elms[i]);
        buf[i] = '\0';

        printf("%016jx %c %d %s\n", offset, node->type, node->count, buf);
}

/*
 * Top level recovery processor.  Assume the data is a B-Tree node.
 * If the CRC is good we attempt to process the node, building the
 * object space and creating the dictionary as we go.
 */
static void
recover_top(char *ptr, hammer_off_t offset)
{
        hammer_node_ondisk_t node;
        hammer_btree_elm_t elm;
        int maxcount;
        int i;
        int isnode;

        for (node = (void *)ptr; (char *)node < ptr + HAMMER_BUFSIZE; ++node) {
                isnode = hammer_crc_test_btree(node);
                maxcount = hammer_node_max_elements(node->type);

                if (DebugOpt) {
                        if (isnode)
                                print_node(node, offset);
                        else if (DebugOpt > 1)
                                printf("%016jx -\n", offset);
                }
                offset += sizeof(*node);

                if (isnode && node->type == HAMMER_BTREE_TYPE_LEAF) {
                        for (i = 0; i < node->count && i < maxcount; ++i) {
                                elm = &node->elms[i];
                                if (elm->base.btype == HAMMER_BTREE_TYPE_RECORD)
                                        recover_elm(&elm->leaf);
                        }
                }
        }
}

static void
recover_elm(hammer_btree_leaf_elm_t leaf)
{
        struct buffer_info *data_buffer = NULL;
        struct recover_dict *dict;
        struct recover_dict *dict2;
        hammer_data_ondisk_t ondisk;
        hammer_off_t data_offset;
        struct stat st;
        int chunk;
        int len;
        int zfill;
        int64_t file_offset;
        uint16_t pfs_id;
        size_t nlen;
        int fd;
        char *name;
        char *path1;
        char *path2;

        /*
         * Ignore deleted records
         */
        if (leaf->delete_ts)
                return;
        if ((data_offset = leaf->data_offset) != 0)
                ondisk = get_buffer_data(data_offset, &data_buffer, 0);
        else
                ondisk = NULL;
        if (ondisk == NULL)
                goto done;

        len = leaf->data_len;
        chunk = HAMMER_BUFSIZE - ((int)data_offset & HAMMER_BUFMASK);
        if (chunk > len)
                chunk = len;

        if (len < 0 || len > HAMMER_XBUFSIZE || len > chunk)
                goto done;

        pfs_id = lo_to_pfs(leaf->base.localization);

        /*
         * Note that meaning of leaf->base.obj_id differs depending
         * on record type.  For a direntry, leaf->base.obj_id points
         * to its parent inode that this entry is a part of, but not
         * its corresponding inode.
         */
        dict = get_dict(leaf->base.obj_id, pfs_id);

        switch(leaf->base.rec_type) {
        case HAMMER_RECTYPE_INODE:
                /*
                 * We found an inode which also tells us where the file
                 * or directory is in the directory hierarchy.
                 */
                if (VerboseOpt) {
                        printf("inode %016jx:%05d found\n",
                                (uintmax_t)leaf->base.obj_id, pfs_id);
                }
                path1 = recover_path(dict);

                /*
                 * Attach the inode to its parent.  This isn't strictly
                 * necessary because the information is also in the
                 * directory entries, but if we do not find the directory
                 * entry this ensures that the files will still be
                 * reasonably well organized in their proper directories.
                 */
                if ((dict->flags & DICTF_PARENT) == 0 &&
                    dict->obj_id != HAMMER_OBJID_ROOT &&
                    ondisk->inode.parent_obj_id != 0) {
                        dict->flags |= DICTF_PARENT;
                        dict->parent = get_dict(ondisk->inode.parent_obj_id,
                                                pfs_id);
                        if (dict->parent &&
                            (dict->parent->flags & DICTF_MADEDIR) == 0) {
                                dict->parent->flags |= DICTF_MADEDIR;
                                path2 = recover_path(dict->parent);
                                printf("mkdir %s\n", path2);
                                mkdir(path2, 0777);
                                free(path2);
                                path2 = NULL;
                        }
                }
                if (dict->obj_type == 0)
                        dict->obj_type = ondisk->inode.obj_type;
                dict->size = ondisk->inode.size;
                path2 = recover_path(dict);

                if (lstat(path1, &st) == 0) {
                        if (ondisk->inode.obj_type == HAMMER_OBJTYPE_REGFILE) {
                                truncate(path1, dict->size);
                                /* chmod(path1, 0666); */
                        }
                        if (strcmp(path1, path2)) {
                                printf("Rename %s -> %s\n", path1, path2);
                                rename(path1, path2);
                        }
                } else if (ondisk->inode.obj_type == HAMMER_OBJTYPE_REGFILE) {
                        printf("mkinode (file) %s\n", path2);
                        fd = open(path2, O_RDWR|O_CREAT, 0666);
                        if (fd > 0)
                                close(fd);
                } else if (ondisk->inode.obj_type == HAMMER_OBJTYPE_DIRECTORY) {
                        printf("mkinode (dir) %s\n", path2);
                        mkdir(path2, 0777);
                        dict->flags |= DICTF_MADEDIR;
                }
                free(path1);
                free(path2);
                break;
        case HAMMER_RECTYPE_DATA:
                /*
                 * File record data
                 */
                if (leaf->base.obj_id == 0)
                        break;
                if (VerboseOpt) {
                        printf("inode %016jx:%05d data %016jx,%d\n",
                                (uintmax_t)leaf->base.obj_id,
                                pfs_id,
                                (uintmax_t)leaf->base.key - len,
                                len);
                }

                /*
                 * Update the dictionary entry
                 */
                if (dict->obj_type == 0)
                        dict->obj_type = HAMMER_OBJTYPE_REGFILE;

                /*
                 * If the parent directory has not been created we
                 * have to create it (typically a PFS%05d)
                 */
                if (dict->parent &&
                    (dict->parent->flags & DICTF_MADEDIR) == 0) {
                        dict->parent->flags |= DICTF_MADEDIR;
                        path2 = recover_path(dict->parent);
                        printf("mkdir %s\n", path2);
                        mkdir(path2, 0777);
                        free(path2);
                        path2 = NULL;
                }

                /*
                 * Create the file if necessary, report file creations
                 */
                path1 = recover_path(dict);
                if (CachedPath && strcmp(CachedPath, path1) == 0) {
                        fd = CachedFd;
                } else {
                        fd = open(path1, O_CREAT|O_RDWR, 0666);
                }
                if (fd < 0) {
                        printf("Unable to create %s: %s\n",
                                path1, strerror(errno));
                        free(path1);
                        break;
                }
                if ((dict->flags & DICTF_MADEFILE) == 0) {
                        dict->flags |= DICTF_MADEFILE;
                        printf("mkfile %s\n", path1);
                }

                /*
                 * And write the record.  A HAMMER data block is aligned
                 * and may contain trailing zeros after the file EOF.  The
                 * inode record is required to get the actual file size.
                 *
                 * However, when the inode record is not available
                 * we can do a sparse write and that will get it right
                 * most of the time even if the inode record is never
                 * found.
                 */
                file_offset = (int64_t)leaf->base.key - len;
                lseek(fd, (off_t)file_offset, SEEK_SET);
                while (len) {
                        if (dict->size == -1) {
                                for (zfill = chunk - 1; zfill >= 0; --zfill) {
                                        if (((char *)ondisk)[zfill])
                                                break;
                                }
                                ++zfill;
                        } else {
                                zfill = chunk;
                        }

                        if (zfill)
                                write(fd, ondisk, zfill);
                        if (zfill < chunk)
                                lseek(fd, chunk - zfill, SEEK_CUR);

                        len -= chunk;
                        data_offset += chunk;
                        file_offset += chunk;
                        ondisk = get_buffer_data(data_offset, &data_buffer, 0);
                        if (ondisk == NULL)
                                break;
                        chunk = HAMMER_BUFSIZE -
                                ((int)data_offset & HAMMER_BUFMASK);
                        if (chunk > len)
                                chunk = len;
                }
                if (dict->size >= 0 && file_offset > dict->size) {
                        ftruncate(fd, dict->size);
                        /* fchmod(fd, 0666); */
                }

                if (fd == CachedFd) {
                        free(path1);
                } else if (CachedPath) {
                        free(CachedPath);
                        close(CachedFd);
                        CachedPath = path1;
                        CachedFd = fd;
                } else {
                        CachedPath = path1;
                        CachedFd = fd;
                }
                break;
        case HAMMER_RECTYPE_DIRENTRY:
                nlen = len - HAMMER_ENTRY_NAME_OFF;
                if ((int)nlen < 0)      /* illegal length */
                        break;
                if (ondisk->entry.obj_id == 0 ||
                    ondisk->entry.obj_id == HAMMER_OBJID_ROOT)
                        break;
                name = malloc(nlen + 1);
                bcopy(ondisk->entry.name, name, nlen);
                name[nlen] = 0;
                sanitize_string(name);

                if (VerboseOpt) {
                        printf("dir %016jx:%05d entry %016jx \"%s\"\n",
                                (uintmax_t)leaf->base.obj_id,
                                pfs_id,
                                (uintmax_t)ondisk->entry.obj_id,
                                name);
                }

                /*
                 * We can't deal with hardlinks so if the object already
                 * has a name assigned to it we just keep using that name.
                 */
                dict2 = get_dict(ondisk->entry.obj_id, pfs_id);
                path1 = recover_path(dict2);

                if (dict2->name == NULL)
                        dict2->name = name;
                else
                        free(name);

                /*
                 * Attach dict2 to its directory (dict), create the
                 * directory (dict) if necessary.  We must ensure
                 * that the directory entry exists in order to be
                 * able to properly rename() the file without creating
                 * a namespace conflict.
                 */
                if ((dict2->flags & DICTF_PARENT) == 0) {
                        dict2->flags |= DICTF_PARENT;
                        dict2->parent = dict;
                        if ((dict->flags & DICTF_MADEDIR) == 0) {
                                dict->flags |= DICTF_MADEDIR;
                                path2 = recover_path(dict);
                                printf("mkdir %s\n", path2);
                                mkdir(path2, 0777);
                                free(path2);
                                path2 = NULL;
                        }
                }
                path2 = recover_path(dict2);
                if (strcmp(path1, path2) != 0 && lstat(path1, &st) == 0) {
                        printf("Rename %s -> %s\n", path1, path2);
                        rename(path1, path2);
                }
                free(path1);
                free(path2);
                break;
        default:
                /*
                 * Ignore any other record types
                 */
                break;
        }
done:
        rel_buffer(data_buffer);
}

#define RD_HSIZE        32768
#define RD_HMASK        (RD_HSIZE - 1)

struct recover_dict *RDHash[RD_HSIZE];

static
struct recover_dict *
get_dict(int64_t obj_id, uint16_t pfs_id)
{
        struct recover_dict *dict;
        int i;

        if (obj_id == 0)
                return(NULL);

        i = crc32(&obj_id, sizeof(obj_id)) & RD_HMASK;
        for (dict = RDHash[i]; dict; dict = dict->next) {
                if (dict->obj_id == obj_id &&
                    dict->pfs_id == pfs_id) {
                        break;
                }
        }
        if (dict == NULL) {
                dict = malloc(sizeof(*dict));
                bzero(dict, sizeof(*dict));
                dict->obj_id = obj_id;
                dict->pfs_id = pfs_id;
                dict->next = RDHash[i];
                dict->size = -1;
                RDHash[i] = dict;

                /*
                 * Always connect dangling dictionary entries to object 1
                 * (the root of the PFS).
                 *
                 * DICTF_PARENT will not be set until we know what the
                 * real parent directory object is.
                 */
                if (dict->obj_id != HAMMER_OBJID_ROOT)
                        dict->parent = get_dict(HAMMER_OBJID_ROOT, pfs_id);
        }
        return(dict);
}

struct path_info {
        enum { PI_FIGURE, PI_LOAD } state;
        uint16_t pfs_id;
        char *base;
        char *next;
        int len;
};

static void recover_path_helper(struct recover_dict *, struct path_info *);

static
char *
recover_path(struct recover_dict *dict)
{
        struct path_info info;

        /* Find info.len first */
        bzero(&info, sizeof(info));
        info.state = PI_FIGURE;
        recover_path_helper(dict, &info);

        /* Fill in the path */
        info.pfs_id = dict->pfs_id;
        info.base = malloc(info.len);
        info.next = info.base;
        info.state = PI_LOAD;
        recover_path_helper(dict, &info);

        /* Return the path */
        return(info.base);
}

#define STRLEN_OBJID    22      /* "obj_0x%016jx" */
#define STRLEN_PFSID    8       /* "PFS%05d" */

static
void
recover_path_helper(struct recover_dict *dict, struct path_info *info)
{
        /*
         * Calculate path element length
         */
        dict->flags |= DICTF_TRAVERSED;

        switch(info->state) {
        case PI_FIGURE:
                if (dict->obj_id == HAMMER_OBJID_ROOT)
                        info->len += STRLEN_PFSID;
                else if (dict->name)
                        info->len += strlen(dict->name);
                else
                        info->len += STRLEN_OBJID;
                ++info->len;

                if (dict->parent &&
                    (dict->parent->flags & DICTF_TRAVERSED) == 0) {
                        recover_path_helper(dict->parent, info);
                } else {
                        info->len += strlen(TargetDir) + 1;
                }
                break;
        case PI_LOAD:
                if (dict->parent &&
                    (dict->parent->flags & DICTF_TRAVERSED) == 0) {
                        recover_path_helper(dict->parent, info);
                } else {
                        strcpy(info->next, TargetDir);
                        info->next += strlen(info->next);
                }

                *info->next++ = '/';
                if (dict->obj_id == HAMMER_OBJID_ROOT) {
                        snprintf(info->next, STRLEN_PFSID + 1,
                                "PFS%05d", info->pfs_id);
                } else if (dict->name) {
                        strcpy(info->next, dict->name);
                } else {
                        snprintf(info->next, STRLEN_OBJID + 1,
                                "obj_0x%016jx", (uintmax_t)dict->obj_id);
                }
                info->next += strlen(info->next);
                break;
        }
        dict->flags &= ~DICTF_TRAVERSED;
}

static
void
sanitize_string(char *str)
{
        while (*str) {
                if (!isprint(*str))
                        *str = 'x';
                ++str;
        }
}

static
hammer_off_t
scan_raw_limit(void)
{
        struct volume_info *vol;
        hammer_blockmap_t rootmap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        struct buffer_info *buffer1 = NULL;
        struct buffer_info *buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t phys_offset;
        hammer_off_t block_offset;
        hammer_off_t offset = 0;
        int zone = HAMMER_ZONE_FREEMAP_INDEX;

        vol = get_root_volume();
        rootmap = &vol->ondisk->vol0_blockmap[zone];
        assert(rootmap->phys_offset != 0);

        for (phys_offset = HAMMER_ZONE_ENCODE(zone, 0);
             phys_offset < HAMMER_ZONE_ENCODE(zone, HAMMER_OFF_LONG_MASK);
             phys_offset += HAMMER_BLOCKMAP_LAYER2) {
                /*
                 * Dive layer 1.
                 */
                layer1_offset = rootmap->phys_offset +
                                HAMMER_BLOCKMAP_LAYER1_OFFSET(phys_offset);
                layer1 = get_buffer_data(layer1_offset, &buffer1, 0);

                if (!hammer_crc_test_layer1(layer1)) {
                        offset = 0; /* failed */
                        goto end;
                }
                if (layer1->phys_offset == HAMMER_BLOCKMAP_UNAVAIL)
                        continue;

                for (block_offset = 0;
                     block_offset < HAMMER_BLOCKMAP_LAYER2;
                     block_offset += HAMMER_BIGBLOCK_SIZE) {
                        /*
                         * Dive layer 2, each entry represents a big-block.
                         */
                        layer2_offset = layer1->phys_offset +
                                        HAMMER_BLOCKMAP_LAYER2_OFFSET(block_offset);
                        layer2 = get_buffer_data(layer2_offset, &buffer2, 0);

                        if (!hammer_crc_test_layer2(layer2)) {
                                offset = 0; /* failed */
                                goto end;
                        }
                        if (layer2->zone == HAMMER_ZONE_UNAVAIL_INDEX) {
                                break;
                        } else if (layer2->zone && layer2->zone != zone) {
                                offset = phys_offset + block_offset;
                        }
                }
        }
end:
        rel_buffer(buffer1);
        rel_buffer(buffer2);

        return(hammer_xlate_to_zone2(offset));
}

static
void
scan_bigblocks(int target_zone)
{
        struct volume_info *vol;
        hammer_blockmap_t rootmap;
        hammer_blockmap_layer1_t layer1;
        hammer_blockmap_layer2_t layer2;
        struct buffer_info *buffer1 = NULL;
        struct buffer_info *buffer2 = NULL;
        hammer_off_t layer1_offset;
        hammer_off_t layer2_offset;
        hammer_off_t phys_offset;
        hammer_off_t block_offset;
        hammer_off_t offset = 0;
        int zone = HAMMER_ZONE_FREEMAP_INDEX;

        vol = get_root_volume();
        rootmap = &vol->ondisk->vol0_blockmap[zone];
        assert(rootmap->phys_offset != 0);

        for (phys_offset = HAMMER_ZONE_ENCODE(zone, 0);
             phys_offset < HAMMER_ZONE_ENCODE(zone, HAMMER_OFF_LONG_MASK);
             phys_offset += HAMMER_BLOCKMAP_LAYER2) {
                /*
                 * Dive layer 1.
                 */
                layer1_offset = rootmap->phys_offset +
                                HAMMER_BLOCKMAP_LAYER1_OFFSET(phys_offset);
                layer1 = get_buffer_data(layer1_offset, &buffer1, 0);

                /*
                if (!hammer_crc_test_layer1(layer1)) {
                }
                */
                if (layer1->phys_offset == HAMMER_BLOCKMAP_UNAVAIL)
                        continue;

                for (block_offset = 0;
                     block_offset < HAMMER_BLOCKMAP_LAYER2;
                     block_offset += HAMMER_BIGBLOCK_SIZE) {
                        offset = phys_offset + block_offset;
                        /*
                         * Dive layer 2, each entry represents a big-block.
                         */
                        layer2_offset = layer1->phys_offset +
                                        HAMMER_BLOCKMAP_LAYER2_OFFSET(block_offset);
                        layer2 = get_buffer_data(layer2_offset, &buffer2, 0);

                        /*
                        if (!hammer_crc_test_layer2(layer2)) {
                        }
                        */
                        if (layer2->zone == target_zone) {
                                add_bigblock_entry(offset, layer1, layer2);
                        } else if (layer2->zone == HAMMER_ZONE_UNAVAIL_INDEX) {
                                break;
                        }
                }
        }
        rel_buffer(buffer1);
        rel_buffer(buffer2);
}

static
void
free_bigblocks(void)
{
        bigblock_t b;

        while ((b = RB_ROOT(&ZoneTree)) != NULL) {
                RB_REMOVE(bigblock_rb_tree, &ZoneTree, b);
                free(b);
        }
        assert(RB_EMPTY(&ZoneTree));
}

static
void
add_bigblock_entry(hammer_off_t offset,
        hammer_blockmap_layer1_t layer1, hammer_blockmap_layer2_t layer2)
{
        bigblock_t b;

        b = calloc(sizeof(*b), 1);
        b->phys_offset = hammer_xlate_to_zone2(offset);
        assert((b->phys_offset & HAMMER_BIGBLOCK_MASK64) == 0);
        bcopy(layer1, &b->layer1, sizeof(*layer1));
        bcopy(layer2, &b->layer2, sizeof(*layer2));

        RB_INSERT(bigblock_rb_tree, &ZoneTree, b);
}

static
bigblock_t
get_bigblock_entry(hammer_off_t offset)
{
        bigblock_t b;

        offset = hammer_xlate_to_zone2(offset);
        offset &= ~HAMMER_BIGBLOCK_MASK64;

        b = RB_LOOKUP(bigblock_rb_tree, &ZoneTree, offset);
        if (b)
                return(b);
        return(NULL);
}