/*
 * fs/logfs/journal.c   - journal handling code
 *
 * As should be obvious for Linux kernel code, license is GPLv2
 *
 * Copyright (c) 2005-2008 Joern Engel <joern@logfs.org>
 */
#include "logfs.h"
#include <linux/slab.h>

static void logfs_calc_free(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        u64 reserve, no_segs = super->s_no_segs;
        s64 free;
        int i;

        /* superblock segments */
        no_segs -= 2;
        super->s_no_journal_segs = 0;
        /* journal */
        journal_for_each(i)
                if (super->s_journal_seg[i]) {
                        no_segs--;
                        super->s_no_journal_segs++;
                }

        /* open segments plus one extra per level for GC */
        no_segs -= 2 * super->s_total_levels;

        free = no_segs * (super->s_segsize - LOGFS_SEGMENT_RESERVE);
        free -= super->s_used_bytes;
        /* just a bit extra */
        free -= super->s_total_levels * 4096;

        /* Bad blocks are 'paid' for with speed reserve - the filesystem
         * simply gets slower as bad blocks accumulate.  Until the bad blocks
         * exceed the speed reserve - then the filesystem gets smaller.
         */
        reserve = super->s_bad_segments + super->s_bad_seg_reserve;
        reserve *= super->s_segsize - LOGFS_SEGMENT_RESERVE;
        reserve = max(reserve, super->s_speed_reserve);
        free -= reserve;
        if (free < 0)
                free = 0;

        super->s_free_bytes = free;
}

static void reserve_sb_and_journal(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct btree_head32 *head = &super->s_reserved_segments;
        int i, err;

        err = btree_insert32(head, seg_no(sb, super->s_sb_ofs[0]), (void *)1,
                        GFP_KERNEL);
        BUG_ON(err);

        err = btree_insert32(head, seg_no(sb, super->s_sb_ofs[1]), (void *)1,
                        GFP_KERNEL);
        BUG_ON(err);

        journal_for_each(i) {
                if (!super->s_journal_seg[i])
                        continue;
                err = btree_insert32(head, super->s_journal_seg[i], (void *)1,
                                GFP_KERNEL);
                BUG_ON(err);
        }
}

static void read_dynsb(struct super_block *sb,
                struct logfs_je_dynsb *dynsb)
{
        struct logfs_super *super = logfs_super(sb);

        super->s_gec            = be64_to_cpu(dynsb->ds_gec);
        super->s_sweeper        = be64_to_cpu(dynsb->ds_sweeper);
        super->s_victim_ino     = be64_to_cpu(dynsb->ds_victim_ino);
        super->s_rename_dir     = be64_to_cpu(dynsb->ds_rename_dir);
        super->s_rename_pos     = be64_to_cpu(dynsb->ds_rename_pos);
        super->s_used_bytes     = be64_to_cpu(dynsb->ds_used_bytes);
        super->s_generation     = be32_to_cpu(dynsb->ds_generation);
}

static void read_anchor(struct super_block *sb,
                struct logfs_je_anchor *da)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode = super->s_master_inode;
        struct logfs_inode *li = logfs_inode(inode);
        int i;

        super->s_last_ino = be64_to_cpu(da->da_last_ino);
        li->li_flags    = 0;
        li->li_height   = da->da_height;
        i_size_write(inode, be64_to_cpu(da->da_size));
        li->li_used_bytes = be64_to_cpu(da->da_used_bytes);

        for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                li->li_data[i] = be64_to_cpu(da->da_data[i]);
}

static void read_erasecount(struct super_block *sb,
                struct logfs_je_journal_ec *ec)
{
        struct logfs_super *super = logfs_super(sb);
        int i;

        journal_for_each(i)
                super->s_journal_ec[i] = be32_to_cpu(ec->ec[i]);
}

static int read_area(struct super_block *sb, struct logfs_je_area *a)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_area[a->gc_level];
        u64 ofs;
        u32 writemask = ~(super->s_writesize - 1);

        if (a->gc_level >= LOGFS_NO_AREAS)
                return -EIO;
        if (a->vim != VIM_DEFAULT)
                return -EIO; /* TODO: close area and continue */

        area->a_used_bytes = be32_to_cpu(a->used_bytes);
        area->a_written_bytes = area->a_used_bytes & writemask;
        area->a_segno = be32_to_cpu(a->segno);
        if (area->a_segno)
                area->a_is_open = 1;

        ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
        if (super->s_writesize > 1)
                return logfs_buf_recover(area, ofs, a + 1, super->s_writesize);
        else
                return logfs_buf_recover(area, ofs, NULL, 0);
}

static void *unpack(void *from, void *to)
{
        struct logfs_journal_header *jh = from;
        void *data = from + sizeof(struct logfs_journal_header);
        int err;
        size_t inlen, outlen;

        inlen = be16_to_cpu(jh->h_len);
        outlen = be16_to_cpu(jh->h_datalen);

        if (jh->h_compr == COMPR_NONE)
                memcpy(to, data, inlen);
        else {
                err = logfs_uncompress(data, to, inlen, outlen);
                BUG_ON(err);
        }
        return to;
}

static int __read_je_header(struct super_block *sb, u64 ofs,
                struct logfs_journal_header *jh)
{
        struct logfs_super *super = logfs_super(sb);
        size_t bufsize = max_t(size_t, sb->s_blocksize, super->s_writesize)
                + MAX_JOURNAL_HEADER;
        u16 type, len, datalen;
        int err;

        /* read header only */
        err = wbuf_read(sb, ofs, sizeof(*jh), jh);
        if (err)
                return err;
        type = be16_to_cpu(jh->h_type);
        len = be16_to_cpu(jh->h_len);
        datalen = be16_to_cpu(jh->h_datalen);
        if (len > sb->s_blocksize)
                return -EIO;
        if ((type < JE_FIRST) || (type > JE_LAST))
                return -EIO;
        if (datalen > bufsize)
                return -EIO;
        return 0;
}

static int __read_je_payload(struct super_block *sb, u64 ofs,
                struct logfs_journal_header *jh)
{
        u16 len;
        int err;

        len = be16_to_cpu(jh->h_len);
        err = wbuf_read(sb, ofs + sizeof(*jh), len, jh + 1);
        if (err)
                return err;
        if (jh->h_crc != logfs_crc32(jh, len + sizeof(*jh), 4)) {
                /* Old code was confused.  It forgot about the header length
                 * and stopped calculating the crc 16 bytes before the end
                 * of data - ick!
                 * FIXME: Remove this hack once the old code is fixed.
                 */
                if (jh->h_crc == logfs_crc32(jh, len, 4))
                        WARN_ON_ONCE(1);
                else
                        return -EIO;
        }
        return 0;
}

/*
 * jh needs to be large enough to hold the complete entry, not just the header
 */
static int __read_je(struct super_block *sb, u64 ofs,
                struct logfs_journal_header *jh)
{
        int err;

        err = __read_je_header(sb, ofs, jh);
        if (err)
                return err;
        return __read_je_payload(sb, ofs, jh);
}

static int read_je(struct super_block *sb, u64 ofs)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_journal_header *jh = super->s_compressed_je;
        void *scratch = super->s_je;
        u16 type, datalen;
        int err;

        err = __read_je(sb, ofs, jh);
        if (err)
                return err;
        type = be16_to_cpu(jh->h_type);
        datalen = be16_to_cpu(jh->h_datalen);

        switch (type) {
        case JE_DYNSB:
                read_dynsb(sb, unpack(jh, scratch));
                break;
        case JE_ANCHOR:
                read_anchor(sb, unpack(jh, scratch));
                break;
        case JE_ERASECOUNT:
                read_erasecount(sb, unpack(jh, scratch));
                break;
        case JE_AREA:
                err = read_area(sb, unpack(jh, scratch));
                break;
        case JE_OBJ_ALIAS:
                err = logfs_load_object_aliases(sb, unpack(jh, scratch),
                                datalen);
                break;
        default:
                WARN_ON_ONCE(1);
                return -EIO;
        }
        return err;
}

static int logfs_read_segment(struct super_block *sb, u32 segno)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_journal_header *jh = super->s_compressed_je;
        u64 ofs, seg_ofs = dev_ofs(sb, segno, 0);
        u32 h_ofs, last_ofs = 0;
        u16 len, datalen, last_len = 0;
        int i, err;

        /* search for most recent commit */
        for (h_ofs = 0; h_ofs < super->s_segsize; h_ofs += sizeof(*jh)) {
                ofs = seg_ofs + h_ofs;
                err = __read_je_header(sb, ofs, jh);
                if (err)
                        continue;
                if (jh->h_type != cpu_to_be16(JE_COMMIT))
                        continue;
                err = __read_je_payload(sb, ofs, jh);
                if (err)
                        continue;
                len = be16_to_cpu(jh->h_len);
                datalen = be16_to_cpu(jh->h_datalen);
                if ((datalen > sizeof(super->s_je_array)) ||
                                (datalen % sizeof(__be64)))
                        continue;
                last_ofs = h_ofs;
                last_len = datalen;
                h_ofs += ALIGN(len, sizeof(*jh)) - sizeof(*jh);
        }
        /* read commit */
        if (last_ofs == 0)
                return -ENOENT;
        ofs = seg_ofs + last_ofs;
        log_journal("Read commit from %llx\n", ofs);
        err = __read_je(sb, ofs, jh);
        BUG_ON(err); /* We should have caught it in the scan loop already */
        if (err)
                return err;
        /* uncompress */
        unpack(jh, super->s_je_array);
        super->s_no_je = last_len / sizeof(__be64);
        /* iterate over array */
        for (i = 0; i < super->s_no_je; i++) {
                err = read_je(sb, be64_to_cpu(super->s_je_array[i]));
                if (err)
                        return err;
        }
        super->s_journal_area->a_segno = segno;
        return 0;
}

static u64 read_gec(struct super_block *sb, u32 segno)
{
        struct logfs_segment_header sh;
        __be32 crc;
        int err;

        if (!segno)
                return 0;
        err = wbuf_read(sb, dev_ofs(sb, segno, 0), sizeof(sh), &sh);
        if (err)
                return 0;
        crc = logfs_crc32(&sh, sizeof(sh), 4);
        if (crc != sh.crc) {
                WARN_ON(sh.gec != cpu_to_be64(0xffffffffffffffffull));
                /* Most likely it was just erased */
                return 0;
        }
        return be64_to_cpu(sh.gec);
}

static int logfs_read_journal(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        u64 gec[LOGFS_JOURNAL_SEGS], max;
        u32 segno;
        int i, max_i;

        max = 0;
        max_i = -1;
        journal_for_each(i) {
                segno = super->s_journal_seg[i];
                gec[i] = read_gec(sb, super->s_journal_seg[i]);
                if (gec[i] > max) {
                        max = gec[i];
                        max_i = i;
                }
        }
        if (max_i == -1)
                return -EIO;
        /* FIXME: Try older segments in case of error */
        return logfs_read_segment(sb, super->s_journal_seg[max_i]);
}

/*
 * First search the current segment (outer loop), then pick the next segment
 * in the array, skipping any zero entries (inner loop).
 */
static void journal_get_free_segment(struct logfs_area *area)
{
        struct logfs_super *super = logfs_super(area->a_sb);
        int i;

        journal_for_each(i) {
                if (area->a_segno != super->s_journal_seg[i])
                        continue;

                do {
                        i++;
                        if (i == LOGFS_JOURNAL_SEGS)
                                i = 0;
                } while (!super->s_journal_seg[i]);

                area->a_segno = super->s_journal_seg[i];
                area->a_erase_count = ++(super->s_journal_ec[i]);
                log_journal("Journal now at %x (ec %x)\n", area->a_segno,
                                area->a_erase_count);
                return;
        }
        BUG();
}

static void journal_get_erase_count(struct logfs_area *area)
{
        /* erase count is stored globally and incremented in
         * journal_get_free_segment() - nothing to do here */
}

static int journal_erase_segment(struct logfs_area *area)
{
        struct super_block *sb = area->a_sb;
        union {
                struct logfs_segment_header sh;
                unsigned char c[ALIGN(sizeof(struct logfs_segment_header), 16)];
        } u;
        u64 ofs;
        int err;

        err = logfs_erase_segment(sb, area->a_segno, 1);
        if (err)
                return err;

        memset(&u, 0, sizeof(u));
        u.sh.pad = 0;
        u.sh.type = SEG_JOURNAL;
        u.sh.level = 0;
        u.sh.segno = cpu_to_be32(area->a_segno);
        u.sh.ec = cpu_to_be32(area->a_erase_count);
        u.sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
        u.sh.crc = logfs_crc32(&u.sh, sizeof(u.sh), 4);

        /* This causes a bug in segment.c.  Not yet. */
        //logfs_set_segment_erased(sb, area->a_segno, area->a_erase_count, 0);

        ofs = dev_ofs(sb, area->a_segno, 0);
        area->a_used_bytes = sizeof(u);
        logfs_buf_write(area, ofs, &u, sizeof(u));
        return 0;
}

static size_t __logfs_write_header(struct logfs_super *super,
                struct logfs_journal_header *jh, size_t len, size_t datalen,
                u16 type, u8 compr)
{
        jh->h_len       = cpu_to_be16(len);
        jh->h_type      = cpu_to_be16(type);
        jh->h_datalen   = cpu_to_be16(datalen);
        jh->h_compr     = compr;
        jh->h_pad[0]    = 'H';
        jh->h_pad[1]    = 'E';
        jh->h_pad[2]    = 'A';
        jh->h_pad[3]    = 'D';
        jh->h_pad[4]    = 'R';
        jh->h_crc       = logfs_crc32(jh, len + sizeof(*jh), 4);
        return ALIGN(len, 16) + sizeof(*jh);
}

static size_t logfs_write_header(struct logfs_super *super,
                struct logfs_journal_header *jh, size_t datalen, u16 type)
{
        size_t len = datalen;

        return __logfs_write_header(super, jh, len, datalen, type, COMPR_NONE);
}

static inline size_t logfs_journal_erasecount_size(struct logfs_super *super)
{
        return LOGFS_JOURNAL_SEGS * sizeof(__be32);
}

static void *logfs_write_erasecount(struct super_block *sb, void *_ec,
                u16 *type, size_t *len)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_je_journal_ec *ec = _ec;
        int i;

        journal_for_each(i)
                ec->ec[i] = cpu_to_be32(super->s_journal_ec[i]);
        *type = JE_ERASECOUNT;
        *len = logfs_journal_erasecount_size(super);
        return ec;
}

static void account_shadow(void *_shadow, unsigned long _sb, u64 ignore,
                size_t ignore2)
{
        struct logfs_shadow *shadow = _shadow;
        struct super_block *sb = (void *)_sb;
        struct logfs_super *super = logfs_super(sb);

        /* consume new space */
        super->s_free_bytes       -= shadow->new_len;
        super->s_used_bytes       += shadow->new_len;
        super->s_dirty_used_bytes -= shadow->new_len;

        /* free up old space */
        super->s_free_bytes       += shadow->old_len;
        super->s_used_bytes       -= shadow->old_len;
        super->s_dirty_free_bytes -= shadow->old_len;

        logfs_set_segment_used(sb, shadow->old_ofs, -shadow->old_len);
        logfs_set_segment_used(sb, shadow->new_ofs, shadow->new_len);

        log_journal("account_shadow(%llx, %llx, %x) %llx->%llx %x->%x\n",
                        shadow->ino, shadow->bix, shadow->gc_level,
                        shadow->old_ofs, shadow->new_ofs,
                        shadow->old_len, shadow->new_len);
        mempool_free(shadow, super->s_shadow_pool);
}

static void account_shadows(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct inode *inode = super->s_master_inode;
        struct logfs_inode *li = logfs_inode(inode);
        struct shadow_tree *tree = &super->s_shadow_tree;

        btree_grim_visitor64(&tree->new, (unsigned long)sb, account_shadow);
        btree_grim_visitor64(&tree->old, (unsigned long)sb, account_shadow);
        btree_grim_visitor32(&tree->segment_map, 0, NULL);
        tree->no_shadowed_segments = 0;

        if (li->li_block) {
                /*
                 * We never actually use the structure, when attached to the
                 * master inode.  But it is easier to always free it here than
                 * to have checks in several places elsewhere when allocating
                 * it.
                 */
                li->li_block->ops->free_block(sb, li->li_block);
        }
        BUG_ON((s64)li->li_used_bytes < 0);
}

static void *__logfs_write_anchor(struct super_block *sb, void *_da,
                u16 *type, size_t *len)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_je_anchor *da = _da;
        struct inode *inode = super->s_master_inode;
        struct logfs_inode *li = logfs_inode(inode);
        int i;

        da->da_height   = li->li_height;
        da->da_last_ino = cpu_to_be64(super->s_last_ino);
        da->da_size     = cpu_to_be64(i_size_read(inode));
        da->da_used_bytes = cpu_to_be64(li->li_used_bytes);
        for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
                da->da_data[i] = cpu_to_be64(li->li_data[i]);
        *type = JE_ANCHOR;
        *len = sizeof(*da);
        return da;
}

static void *logfs_write_dynsb(struct super_block *sb, void *_dynsb,
                u16 *type, size_t *len)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_je_dynsb *dynsb = _dynsb;

        dynsb->ds_gec           = cpu_to_be64(super->s_gec);
        dynsb->ds_sweeper       = cpu_to_be64(super->s_sweeper);
        dynsb->ds_victim_ino    = cpu_to_be64(super->s_victim_ino);
        dynsb->ds_rename_dir    = cpu_to_be64(super->s_rename_dir);
        dynsb->ds_rename_pos    = cpu_to_be64(super->s_rename_pos);
        dynsb->ds_used_bytes    = cpu_to_be64(super->s_used_bytes);
        dynsb->ds_generation    = cpu_to_be32(super->s_generation);
        *type = JE_DYNSB;
        *len = sizeof(*dynsb);
        return dynsb;
}

static void write_wbuf(struct super_block *sb, struct logfs_area *area,
                void *wbuf)
{
        struct logfs_super *super = logfs_super(sb);
        struct address_space *mapping = super->s_mapping_inode->i_mapping;
        u64 ofs;
        pgoff_t index;
        int page_ofs;
        struct page *page;

        ofs = dev_ofs(sb, area->a_segno,
                        area->a_used_bytes & ~(super->s_writesize - 1));
        index = ofs >> PAGE_SHIFT;
        page_ofs = ofs & (PAGE_SIZE - 1);

        page = find_or_create_page(mapping, index, GFP_NOFS);
        BUG_ON(!page);
        memcpy(wbuf, page_address(page) + page_ofs, super->s_writesize);
        unlock_page(page);
}

static void *logfs_write_area(struct super_block *sb, void *_a,
                u16 *type, size_t *len)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_area[super->s_sum_index];
        struct logfs_je_area *a = _a;

        a->vim = VIM_DEFAULT;
        a->gc_level = super->s_sum_index;
        a->used_bytes = cpu_to_be32(area->a_used_bytes);
        a->segno = cpu_to_be32(area->a_segno);
        if (super->s_writesize > 1)
                write_wbuf(sb, area, a + 1);

        *type = JE_AREA;
        *len = sizeof(*a) + super->s_writesize;
        return a;
}

static void *logfs_write_commit(struct super_block *sb, void *h,
                u16 *type, size_t *len)
{
        struct logfs_super *super = logfs_super(sb);

        *type = JE_COMMIT;
        *len = super->s_no_je * sizeof(__be64);
        return super->s_je_array;
}

static size_t __logfs_write_je(struct super_block *sb, void *buf, u16 type,
                size_t len)
{
        struct logfs_super *super = logfs_super(sb);
        void *header = super->s_compressed_je;
        void *data = header + sizeof(struct logfs_journal_header);
        ssize_t compr_len, pad_len;
        u8 compr = COMPR_ZLIB;

        if (len == 0)
                return logfs_write_header(super, header, 0, type);

        compr_len = logfs_compress(buf, data, len, sb->s_blocksize);
        if (compr_len < 0 || type == JE_ANCHOR) {
                memcpy(data, buf, len);
                compr_len = len;
                compr = COMPR_NONE;
        }

        pad_len = ALIGN(compr_len, 16);
        memset(data + compr_len, 0, pad_len - compr_len);

        return __logfs_write_header(super, header, compr_len, len, type, compr);
}

static s64 logfs_get_free_bytes(struct logfs_area *area, size_t *bytes,
                int must_pad)
{
        u32 writesize = logfs_super(area->a_sb)->s_writesize;
        s32 ofs;
        int ret;

        ret = logfs_open_area(area, *bytes);
        if (ret)
                return -EAGAIN;

        ofs = area->a_used_bytes;
        area->a_used_bytes += *bytes;

        if (must_pad) {
                area->a_used_bytes = ALIGN(area->a_used_bytes, writesize);
                *bytes = area->a_used_bytes - ofs;
        }

        return dev_ofs(area->a_sb, area->a_segno, ofs);
}

static int logfs_write_je_buf(struct super_block *sb, void *buf, u16 type,
                size_t buf_len)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_journal_area;
        struct logfs_journal_header *jh = super->s_compressed_je;
        size_t len;
        int must_pad = 0;
        s64 ofs;

        len = __logfs_write_je(sb, buf, type, buf_len);
        if (jh->h_type == cpu_to_be16(JE_COMMIT))
                must_pad = 1;

        ofs = logfs_get_free_bytes(area, &len, must_pad);
        if (ofs < 0)
                return ofs;
        logfs_buf_write(area, ofs, super->s_compressed_je, len);
        BUG_ON(super->s_no_je >= MAX_JOURNAL_ENTRIES);
        super->s_je_array[super->s_no_je++] = cpu_to_be64(ofs);
        return 0;
}

static int logfs_write_je(struct super_block *sb,
                void* (*write)(struct super_block *sb, void *scratch,
                        u16 *type, size_t *len))
{
        void *buf;
        size_t len;
        u16 type;

        buf = write(sb, logfs_super(sb)->s_je, &type, &len);
        return logfs_write_je_buf(sb, buf, type, len);
}

int write_alias_journal(struct super_block *sb, u64 ino, u64 bix,
                level_t level, int child_no, __be64 val)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_obj_alias *oa = super->s_je;
        int err = 0, fill = super->s_je_fill;

        log_aliases("logfs_write_obj_aliases #%x(%llx, %llx, %x, %x) %llx\n",
                        fill, ino, bix, level, child_no, be64_to_cpu(val));
        oa[fill].ino = cpu_to_be64(ino);
        oa[fill].bix = cpu_to_be64(bix);
        oa[fill].val = val;
        oa[fill].level = (__force u8)level;
        oa[fill].child_no = cpu_to_be16(child_no);
        fill++;
        if (fill >= sb->s_blocksize / sizeof(*oa)) {
                err = logfs_write_je_buf(sb, oa, JE_OBJ_ALIAS, sb->s_blocksize);
                fill = 0;
        }

        super->s_je_fill = fill;
        return err;
}

static int logfs_write_obj_aliases(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        int err;

        log_journal("logfs_write_obj_aliases: %d aliases to write\n",
                        super->s_no_object_aliases);
        super->s_je_fill = 0;
        err = logfs_write_obj_aliases_pagecache(sb);
        if (err)
                return err;

        if (super->s_je_fill)
                err = logfs_write_je_buf(sb, super->s_je, JE_OBJ_ALIAS,
                                super->s_je_fill
                                * sizeof(struct logfs_obj_alias));
        return err;
}

/*
 * Write all journal entries.  The goto logic ensures that all journal entries
 * are written whenever a new segment is used.  It is ugly and potentially a
 * bit wasteful, but robustness is more important.  With this we can *always*
 * erase all journal segments except the one containing the most recent commit.
 */
void logfs_write_anchor(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_journal_area;
        int i, err;

        if (!(super->s_flags & LOGFS_SB_FLAG_DIRTY))
                return;
        super->s_flags &= ~LOGFS_SB_FLAG_DIRTY;

        BUG_ON(super->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
        mutex_lock(&super->s_journal_mutex);

        /* Do this first or suffer corruption */
        logfs_sync_segments(sb);
        account_shadows(sb);

again:
        super->s_no_je = 0;
        for_each_area(i) {
                if (!super->s_area[i]->a_is_open)
                        continue;
                super->s_sum_index = i;
                err = logfs_write_je(sb, logfs_write_area);
                if (err)
                        goto again;
        }
        err = logfs_write_obj_aliases(sb);
        if (err)
                goto again;
        err = logfs_write_je(sb, logfs_write_erasecount);
        if (err)
                goto again;
        err = logfs_write_je(sb, __logfs_write_anchor);
        if (err)
                goto again;
        err = logfs_write_je(sb, logfs_write_dynsb);
        if (err)
                goto again;
        /*
         * Order is imperative.  First we sync all writes, including the
         * non-committed journal writes.  Then we write the final commit and
         * sync the current journal segment.
         * There is a theoretical bug here.  Syncing the journal segment will
         * write a number of journal entries and the final commit.  All these
         * are written in a single operation.  If the device layer writes the
         * data back-to-front, the commit will precede the other journal
         * entries, leaving a race window.
         * Two fixes are possible.  Preferred is to fix the device layer to
         * ensure writes happen front-to-back.  Alternatively we can insert
         * another logfs_sync_area() super->s_devops->sync() combo before
         * writing the commit.
         */
        /*
         * On another subject, super->s_devops->sync is usually not necessary.
         * Unless called from sys_sync or friends, a barrier would suffice.
         */
        super->s_devops->sync(sb);
        err = logfs_write_je(sb, logfs_write_commit);
        if (err)
                goto again;
        log_journal("Write commit to %llx\n",
                        be64_to_cpu(super->s_je_array[super->s_no_je - 1]));
        logfs_sync_area(area);
        BUG_ON(area->a_used_bytes != area->a_written_bytes);
        super->s_devops->sync(sb);

        mutex_unlock(&super->s_journal_mutex);
        return;
}

void do_logfs_journal_wl_pass(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        struct logfs_area *area = super->s_journal_area;
        struct btree_head32 *head = &super->s_reserved_segments;
        u32 segno, ec;
        int i, err;

        log_journal("Journal requires wear-leveling.\n");
        /* Drop old segments */
        journal_for_each(i)
                if (super->s_journal_seg[i]) {
                        btree_remove32(head, super->s_journal_seg[i]);
                        logfs_set_segment_unreserved(sb,
                                        super->s_journal_seg[i],
                                        super->s_journal_ec[i]);
                        super->s_journal_seg[i] = 0;
                        super->s_journal_ec[i] = 0;
                }
        /* Get new segments */
        for (i = 0; i < super->s_no_journal_segs; i++) {
                segno = get_best_cand(sb, &super->s_reserve_list, &ec);
                super->s_journal_seg[i] = segno;
                super->s_journal_ec[i] = ec;
                logfs_set_segment_reserved(sb, segno);
                err = btree_insert32(head, segno, (void *)1, GFP_NOFS);
                BUG_ON(err); /* mempool should prevent this */
                err = logfs_erase_segment(sb, segno, 1);
                BUG_ON(err); /* FIXME: remount-ro would be nicer */
        }
        /* Manually move journal_area */
        freeseg(sb, area->a_segno);
        area->a_segno = super->s_journal_seg[0];
        area->a_is_open = 0;
        area->a_used_bytes = 0;
        /* Write journal */
        logfs_write_anchor(sb);
        /* Write superblocks */
        err = logfs_write_sb(sb);
        BUG_ON(err);
}

static const struct logfs_area_ops journal_area_ops = {
        .get_free_segment       = journal_get_free_segment,
        .get_erase_count        = journal_get_erase_count,
        .erase_segment          = journal_erase_segment,
};

int logfs_init_journal(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);
        size_t bufsize = max_t(size_t, sb->s_blocksize, super->s_writesize)
                + MAX_JOURNAL_HEADER;
        int ret = -ENOMEM;

        mutex_init(&super->s_journal_mutex);
        btree_init_mempool32(&super->s_reserved_segments, super->s_btree_pool);

        super->s_je = kzalloc(bufsize, GFP_KERNEL);
        if (!super->s_je)
                return ret;

        super->s_compressed_je = kzalloc(bufsize, GFP_KERNEL);
        if (!super->s_compressed_je)
                return ret;

        super->s_master_inode = logfs_new_meta_inode(sb, LOGFS_INO_MASTER);
        if (IS_ERR(super->s_master_inode))
                return PTR_ERR(super->s_master_inode);

        ret = logfs_read_journal(sb);
        if (ret)
                return -EIO;

        reserve_sb_and_journal(sb);
        logfs_calc_free(sb);

        super->s_journal_area->a_ops = &journal_area_ops;
        return 0;
}

void logfs_cleanup_journal(struct super_block *sb)
{
        struct logfs_super *super = logfs_super(sb);

        btree_grim_visitor32(&super->s_reserved_segments, 0, NULL);

        kfree(super->s_compressed_je);
        kfree(super->s_je);
}