// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/sysv/itree.c
 *
 *  Handling of indirect blocks' trees.
 *  AV, Sep--Dec 2000
 */

#include <linux/buffer_head.h>
#include <linux/mount.h>
#include <linux/string.h>
#include "sysv.h"

enum {DIRECT = 10, DEPTH = 4};  /* Have triple indirect */

static inline void dirty_indirect(struct buffer_head *bh, struct inode *inode)
{
        mark_buffer_dirty_inode(bh, inode);
        if (IS_SYNC(inode))
                sync_dirty_buffer(bh);
}

static int block_to_path(struct inode *inode, long block, int offsets[DEPTH])
{
        struct super_block *sb = inode->i_sb;
        struct sysv_sb_info *sbi = SYSV_SB(sb);
        int ptrs_bits = sbi->s_ind_per_block_bits;
        unsigned long   indirect_blocks = sbi->s_ind_per_block,
                        double_blocks = sbi->s_ind_per_block_2;
        int n = 0;

        if (block < 0) {
                printk("sysv_block_map: block < 0\n");
        } else if (block < DIRECT) {
                offsets[n++] = block;
        } else if ( (block -= DIRECT) < indirect_blocks) {
                offsets[n++] = DIRECT;
                offsets[n++] = block;
        } else if ((block -= indirect_blocks) < double_blocks) {
                offsets[n++] = DIRECT+1;
                offsets[n++] = block >> ptrs_bits;
                offsets[n++] = block & (indirect_blocks - 1);
        } else if (((block -= double_blocks) >> (ptrs_bits * 2)) < indirect_blocks) {
                offsets[n++] = DIRECT+2;
                offsets[n++] = block >> (ptrs_bits * 2);
                offsets[n++] = (block >> ptrs_bits) & (indirect_blocks - 1);
                offsets[n++] = block & (indirect_blocks - 1);
        } else {
                /* nothing */;
        }
        return n;
}

static inline int block_to_cpu(struct sysv_sb_info *sbi, sysv_zone_t nr)
{
        return sbi->s_block_base + fs32_to_cpu(sbi, nr);
}

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

static DEFINE_RWLOCK(pointers_lock);

static inline void add_chain(Indirect *p, struct buffer_head *bh, sysv_zone_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 sysv_zone_t *block_end(struct buffer_head *bh)
{
        return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
}

/*
 * Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
 */
static Indirect *get_branch(struct inode *inode,
                            int depth,
                            int offsets[],
                            Indirect chain[],
                            int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;

        *err = 0;
        add_chain(chain, NULL, SYSV_I(inode)->i_data + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                int block = block_to_cpu(SYSV_SB(sb), p->key);
                bh = sb_bread(sb, block);
                if (!bh)
                        goto failure;
                if (!verify_chain(chain, p))
                        goto changed;
                add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
                if (!p->key)
                        goto no_block;
        }
        return NULL;

changed:
        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 blocksize = inode->i_sb->s_blocksize;
        int n = 0;
        int i;

        branch[0].key = sysv_new_block(inode->i_sb);
        if (branch[0].key) for (n = 1; n < num; n++) {
                struct buffer_head *bh;
                int parent;
                /* Allocate the next block */
                branch[n].key = sysv_new_block(inode->i_sb);
                if (!branch[n].key)
                        break;
                /*
                 * Get buffer_head for parent block, zero it out and set 
                 * the pointer to new one, then send parent to disk.
                 */
                parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
                bh = sb_getblk(inode->i_sb, parent);
                lock_buffer(bh);
                memset(bh->b_data, 0, blocksize);
                branch[n].bh = bh;
                branch[n].p = (sysv_zone_t*) bh->b_data + offsets[n];
                *branch[n].p = branch[n].key;
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
                dirty_indirect(bh, inode);
        }
        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++)
                sysv_free_block(inode->i_sb, branch[i].key);
        return -ENOSPC;
}

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

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

        inode->i_ctime = current_time(inode);

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

        if (IS_SYNC(inode))
                sysv_sync_inode(inode);
        else
                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++)
                sysv_free_block(inode->i_sb, where[i].key);
        return -EAGAIN;
}

static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
{
        int err = -EIO;
        int offsets[DEPTH];
        Indirect chain[DEPTH];
        struct super_block *sb = inode->i_sb;
        Indirect *partial;
        int left;
        int depth = block_to_path(inode, iblock, offsets);

        if (depth == 0)
                goto out;

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

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
got_it:
                map_bh(bh_result, sb, block_to_cpu(SYSV_SB(sb),
                                        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_result);
        goto got_it;

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

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

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

        *top = 0;
        for (k = depth; k > 1 && !offsets[k-1]; k--)
                ;

        write_lock(&pointers_lock);
        partial = get_branch(inode, k, offsets, chain, &err);
        if (!partial)
                partial = chain + k-1;
        /*
         * If the branch acquired continuation since we've looked at it -
         * fine, it should all survive and (new) top doesn't belong to us.
         */
        if (!partial->key && *partial->p) {
                write_unlock(&pointers_lock);
                goto no_top;
        }
        for (p=partial; p>chain && all_zeroes((sysv_zone_t*)p->bh->b_data,p->p); p--)
                ;
        /*
         * OK, we've found the last block that must survive. The rest of our
         * branch should be detached before unlocking. However, if that rest
         * of branch is all ours and does not grow immediately from the inode
         * it's easier to cheat and just decrement partial->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, sysv_zone_t *p, sysv_zone_t *q)
{
        for ( ; p < q ; p++) {
                sysv_zone_t nr = *p;
                if (nr) {
                        *p = 0;
                        sysv_free_block(inode->i_sb, nr);
                        mark_inode_dirty(inode);
                }
        }
}

static void free_branches(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q, int depth)
{
        struct buffer_head * bh;
        struct super_block *sb = inode->i_sb;

        if (depth--) {
                for ( ; p < q ; p++) {
                        int block;
                        sysv_zone_t nr = *p;
                        if (!nr)
                                continue;
                        *p = 0;
                        block = block_to_cpu(SYSV_SB(sb), nr);
                        bh = sb_bread(sb, block);
                        if (!bh)
                                continue;
                        free_branches(inode, (sysv_zone_t*)bh->b_data,
                                        block_end(bh), depth);
                        bforget(bh);
                        sysv_free_block(sb, nr);
                        mark_inode_dirty(inode);
                }
        } else
                free_data(inode, p, q);
}

void sysv_truncate (struct inode * inode)
{
        sysv_zone_t *i_data = SYSV_I(inode)->i_data;
        int offsets[DEPTH];
        Indirect chain[DEPTH];
        Indirect *partial;
        sysv_zone_t nr = 0;
        int n;
        long iblock;
        unsigned blocksize;

        if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
            S_ISLNK(inode->i_mode)))
                return;

        blocksize = inode->i_sb->s_blocksize;
        iblock = (inode->i_size + blocksize-1)
                                        >> inode->i_sb->s_blocksize_bits;

        block_truncate_page(inode->i_mapping, inode->i_size, get_block);

        n = block_to_path(inode, iblock, offsets);
        if (n == 0)
                return;

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

        partial = find_shared(inode, n, offsets, chain, &nr);
        /* Kill the top of shared branch (already detached) */
        if (nr) {
                if (partial == chain)
                        mark_inode_dirty(inode);
                else
                        dirty_indirect(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);
                dirty_indirect(partial->bh, inode);
                brelse (partial->bh);
                partial--;
        }
do_indirects:
        /* Kill the remaining (whole) subtrees (== subtrees deeper than...) */
        while (n < DEPTH) {
                nr = i_data[DIRECT + n - 1];
                if (nr) {
                        i_data[DIRECT + n - 1] = 0;
                        mark_inode_dirty(inode);
                        free_branches(inode, &nr, &nr+1, n);
                }
                n++;
        }
        inode->i_mtime = inode->i_ctime = current_time(inode);
        if (IS_SYNC(inode))
                sysv_sync_inode (inode);
        else
                mark_inode_dirty(inode);
}

static unsigned sysv_nblocks(struct super_block *s, loff_t size)
{
        struct sysv_sb_info *sbi = SYSV_SB(s);
        int ptrs_bits = sbi->s_ind_per_block_bits;
        unsigned blocks, res, direct = DIRECT, i = DEPTH;
        blocks = (size + s->s_blocksize - 1) >> s->s_blocksize_bits;
        res = blocks;
        while (--i && blocks > direct) {
                blocks = ((blocks - direct - 1) >> ptrs_bits) + 1;
                res += blocks;
                direct = 1;
        }
        return blocks;
}

int sysv_getattr(const struct path *path, struct kstat *stat,
                 u32 request_mask, unsigned int flags)
{
        struct super_block *s = path->dentry->d_sb;
        generic_fillattr(d_inode(path->dentry), stat);
        stat->blocks = (s->s_blocksize / 512) * sysv_nblocks(s, stat->size);
        stat->blksize = s->s_blocksize;
        return 0;
}

static int sysv_writepage(struct page *page, struct writeback_control *wbc)
{
        return block_write_full_page(page,get_block,wbc);
}

static int sysv_readpage(struct file *file, struct page *page)
{
        return block_read_full_page(page,get_block);
}

int sysv_prepare_chunk(struct page *page, loff_t pos, unsigned len)
{
        return __block_write_begin(page, pos, len, get_block);
}

static void sysv_write_failed(struct address_space *mapping, loff_t to)
{
        struct inode *inode = mapping->host;

        if (to > inode->i_size) {
                truncate_pagecache(inode, inode->i_size);
                sysv_truncate(inode);
        }
}

static int sysv_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        int ret;

        ret = block_write_begin(mapping, pos, len, flags, pagep, get_block);
        if (unlikely(ret))
                sysv_write_failed(mapping, pos + len);

        return ret;
}

static sector_t sysv_bmap(struct address_space *mapping, sector_t block)
{
        return generic_block_bmap(mapping,block,get_block);
}

const struct address_space_operations sysv_aops = {
        .readpage = sysv_readpage,
        .writepage = sysv_writepage,
        .write_begin = sysv_write_begin,
        .write_end = generic_write_end,
        .bmap = sysv_bmap
};