// SPDX-License-Identifier: GPL-2.0
/* Generic part */

typedef struct {
        block_t *p;
        block_t key;
        struct buffer_head *bh;
} Indirect;

static DEFINE_RWLOCK(pointers_lock);

static inline void add_chain(Indirect *p, struct buffer_head *bh, block_t *v)
{
        p->key = *(p->p = v);
        p->bh = bh;
}

static inline int verify_chain(Indirect *from, Indirect *to)
{
        while (from <= to && from->key == *from->p)
                from++;
        return (from > to);
}

static inline block_t *block_end(struct buffer_head *bh)
{
        return (block_t *)((char*)bh->b_data + bh->b_size);
}

static inline Indirect *get_branch(struct inode *inode,
                                        int depth,
                                        int *offsets,
                                        Indirect chain[DEPTH],
                                        int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;

        *err = 0;
        /* i_data is not going away, no lock needed */
        add_chain (chain, NULL, i_data(inode) + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                bh = sb_bread(sb, block_to_cpu(p->key));
                if (!bh)
                        goto failure;
                read_lock(&pointers_lock);
                if (!verify_chain(chain, p))
                        goto changed;
                add_chain(++p, bh, (block_t *)bh->b_data + *++offsets);
                read_unlock(&pointers_lock);
                if (!p->key)
                        goto no_block;
        }
        return NULL;

changed:
        read_unlock(&pointers_lock);
        brelse(bh);
        *err = -EAGAIN;
        goto no_block;
failure:
        *err = -EIO;
no_block:
        return p;
}

static int alloc_branch(struct inode *inode,
                             int num,
                             int *offsets,
                             Indirect *branch)
{
        int n = 0;
        int i;
        int parent = minix_new_block(inode);

        branch[0].key = cpu_to_block(parent);
        if (parent) for (n = 1; n < num; n++) {
                struct buffer_head *bh;
                /* Allocate the next block */
                int nr = minix_new_block(inode);
                if (!nr)
                        break;
                branch[n].key = cpu_to_block(nr);
                bh = sb_getblk(inode->i_sb, parent);
                lock_buffer(bh);
                memset(bh->b_data, 0, bh->b_size);
                branch[n].bh = bh;
                branch[n].p = (block_t*) bh->b_data + offsets[n];
                *branch[n].p = branch[n].key;
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
                mark_buffer_dirty_inode(bh, inode);
                parent = nr;
        }
        if (n == num)
                return 0;

        /* Allocation failed, free what we already allocated */
        for (i = 1; i < n; i++)
                bforget(branch[i].bh);
        for (i = 0; i < n; i++)
                minix_free_block(inode, block_to_cpu(branch[i].key));
        return -ENOSPC;
}

static inline int splice_branch(struct inode *inode,
                                     Indirect chain[DEPTH],
                                     Indirect *where,
                                     int num)
{
        int i;

        write_lock(&pointers_lock);

        /* Verify that place we are splicing to is still there and vacant */
        if (!verify_chain(chain, where-1) || *where->p)
                goto changed;

        *where->p = where->key;

        write_unlock(&pointers_lock);

        /* We are done with atomic stuff, now do the rest of housekeeping */

        inode->i_ctime = current_time(inode);

        /* had we spliced it onto indirect block? */
        if (where->bh)
                mark_buffer_dirty_inode(where->bh, inode);

        mark_inode_dirty(inode);
        return 0;

changed:
        write_unlock(&pointers_lock);
        for (i = 1; i < num; i++)
                bforget(where[i].bh);
        for (i = 0; i < num; i++)
                minix_free_block(inode, block_to_cpu(where[i].key));
        return -EAGAIN;
}

static int get_block(struct inode * inode, sector_t block,
                        struct buffer_head *bh, int create)
{
        int err = -EIO;
        int offsets[DEPTH];
        Indirect chain[DEPTH];
        Indirect *partial;
        int left;
        int depth = block_to_path(inode, block, offsets);

        if (depth == 0)
                goto out;

reread:
        partial = get_branch(inode, depth, offsets, chain, &err);

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
got_it:
                map_bh(bh, inode->i_sb, block_to_cpu(chain[depth-1].key));
                /* Clean up and exit */
                partial = chain+depth-1; /* the whole chain */
                goto cleanup;
        }

        /* Next simple case - plain lookup or failed read of indirect block */
        if (!create || err == -EIO) {
cleanup:
                while (partial > chain) {
                        brelse(partial->bh);
                        partial--;
                }
out:
                return err;
        }

        /*
         * Indirect block might be removed by truncate while we were
         * reading it. Handling of that case (forget what we've got and
         * reread) is taken out of the main path.
         */
        if (err == -EAGAIN)
                goto changed;

        left = (chain + depth) - partial;
        err = alloc_branch(inode, left, offsets+(partial-chain), partial);
        if (err)
                goto cleanup;

        if (splice_branch(inode, chain, partial, left) < 0)
                goto changed;

        set_buffer_new(bh);
        goto got_it;

changed:
        while (partial > chain) {
                brelse(partial->bh);
                partial--;
        }
        goto reread;
}

static inline int all_zeroes(block_t *p, block_t *q)
{
        while (p < q)
                if (*p++)
                        return 0;
        return 1;
}

static Indirect *find_shared(struct inode *inode,
                                int depth,
                                int offsets[DEPTH],
                                Indirect chain[DEPTH],
                                block_t *top)
{
        Indirect *partial, *p;
        int k, err;

        *top = 0;
        for (k = depth; k > 1 && !offsets[k-1]; k--)
                ;
        partial = get_branch(inode, k, offsets, chain, &err);

        write_lock(&pointers_lock);
        if (!partial)
                partial = chain + k-1;
        if (!partial->key && *partial->p) {
                write_unlock(&pointers_lock);
                goto no_top;
        }
        for (p=partial;p>chain && all_zeroes((block_t*)p->bh->b_data,p->p);p--)
                ;
        if (p == chain + k - 1 && p > chain) {
                p->p--;
        } else {
                *top = *p->p;
                *p->p = 0;
        }
        write_unlock(&pointers_lock);

        while(partial > p)
        {
                brelse(partial->bh);
                partial--;
        }
no_top:
        return partial;
}

static inline void free_data(struct inode *inode, block_t *p, block_t *q)
{
        unsigned long nr;

        for ( ; p < q ; p++) {
                nr = block_to_cpu(*p);
                if (nr) {
                        *p = 0;
                        minix_free_block(inode, nr);
                }
        }
}

static void free_branches(struct inode *inode, block_t *p, block_t *q, int depth)
{
        struct buffer_head * bh;
        unsigned long nr;

        if (depth--) {
                for ( ; p < q ; p++) {
                        nr = block_to_cpu(*p);
                        if (!nr)
                                continue;
                        *p = 0;
                        bh = sb_bread(inode->i_sb, nr);
                        if (!bh)
                                continue;
                        free_branches(inode, (block_t*)bh->b_data,
                                      block_end(bh), depth);
                        bforget(bh);
                        minix_free_block(inode, nr);
                        mark_inode_dirty(inode);
                }
        } else
                free_data(inode, p, q);
}

static inline void truncate (struct inode * inode)
{
        struct super_block *sb = inode->i_sb;
        block_t *idata = i_data(inode);
        int offsets[DEPTH];
        Indirect chain[DEPTH];
        Indirect *partial;
        block_t nr = 0;
        int n;
        int first_whole;
        long iblock;

        iblock = (inode->i_size + sb->s_blocksize -1) >> sb->s_blocksize_bits;
        block_truncate_page(inode->i_mapping, inode->i_size, get_block);

        n = block_to_path(inode, iblock, offsets);
        if (!n)
                return;

        if (n == 1) {
                free_data(inode, idata+offsets[0], idata + DIRECT);
                first_whole = 0;
                goto do_indirects;
        }

        first_whole = offsets[0] + 1 - DIRECT;
        partial = find_shared(inode, n, offsets, chain, &nr);
        if (nr) {
                if (partial == chain)
                        mark_inode_dirty(inode);
                else
                        mark_buffer_dirty_inode(partial->bh, inode);
                free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
        }
        /* Clear the ends of indirect blocks on the shared branch */
        while (partial > chain) {
                free_branches(inode, partial->p + 1, block_end(partial->bh),
                                (chain+n-1) - partial);
                mark_buffer_dirty_inode(partial->bh, inode);
                brelse (partial->bh);
                partial--;
        }
do_indirects:
        /* Kill the remaining (whole) subtrees */
        while (first_whole < DEPTH-1) {
                nr = idata[DIRECT+first_whole];
                if (nr) {
                        idata[DIRECT+first_whole] = 0;
                        mark_inode_dirty(inode);
                        free_branches(inode, &nr, &nr+1, first_whole+1);
                }
                first_whole++;
        }
        inode->i_mtime = inode->i_ctime = current_time(inode);
        mark_inode_dirty(inode);
}

static inline unsigned nblocks(loff_t size, struct super_block *sb)
{
        int k = sb->s_blocksize_bits - 10;
        unsigned blocks, res, direct = DIRECT, i = DEPTH;
        blocks = (size + sb->s_blocksize - 1) >> (BLOCK_SIZE_BITS + k);
        res = blocks;
        while (--i && blocks > direct) {
                blocks -= direct;
                blocks += sb->s_blocksize/sizeof(block_t) - 1;
                blocks /= sb->s_blocksize/sizeof(block_t);
                res += blocks;
                direct = 1;
        }
        return res;
}