// SPDX-License-Identifier: GPL-2.0-only
/*
 * OMFS (as used by RIO Karma) directory operations.
 * Copyright (C) 2005 Bob Copeland <me@bobcopeland.com>
 */

#include <linux/fs.h>
#include <linux/ctype.h>
#include <linux/buffer_head.h>
#include "omfs.h"

static int omfs_hash(const char *name, int namelen, int mod)
{
        int i, hash = 0;
        for (i = 0; i < namelen; i++)
                hash ^= tolower(name[i]) << (i % 24);
        return hash % mod;
}

/*
 * Finds the bucket for a given name and reads the containing block;
 * *ofs is set to the offset of the first list entry.
 */
static struct buffer_head *omfs_get_bucket(struct inode *dir,
                const char *name, int namelen, int *ofs)
{
        int nbuckets = (dir->i_size - OMFS_DIR_START)/8;
        int bucket = omfs_hash(name, namelen, nbuckets);

        *ofs = OMFS_DIR_START + bucket * 8;
        return omfs_bread(dir->i_sb, dir->i_ino);
}

static struct buffer_head *omfs_scan_list(struct inode *dir, u64 block,
                                const char *name, int namelen,
                                u64 *prev_block)
{
        struct buffer_head *bh;
        struct omfs_inode *oi;
        int err = -ENOENT;
        *prev_block = ~0;

        while (block != ~0) {
                bh = omfs_bread(dir->i_sb, block);
                if (!bh) {
                        err = -EIO;
                        goto err;
                }

                oi = (struct omfs_inode *) bh->b_data;
                if (omfs_is_bad(OMFS_SB(dir->i_sb), &oi->i_head, block)) {
                        brelse(bh);
                        goto err;
                }

                if (strncmp(oi->i_name, name, namelen) == 0)
                        return bh;

                *prev_block = block;
                block = be64_to_cpu(oi->i_sibling);
                brelse(bh);
        }
err:
        return ERR_PTR(err);
}

static struct buffer_head *omfs_find_entry(struct inode *dir,
                                           const char *name, int namelen)
{
        struct buffer_head *bh;
        int ofs;
        u64 block, dummy;

        bh = omfs_get_bucket(dir, name, namelen, &ofs);
        if (!bh)
                return ERR_PTR(-EIO);

        block = be64_to_cpu(*((__be64 *) &bh->b_data[ofs]));
        brelse(bh);

        return omfs_scan_list(dir, block, name, namelen, &dummy);
}

int omfs_make_empty(struct inode *inode, struct super_block *sb)
{
        struct omfs_sb_info *sbi = OMFS_SB(sb);
        struct buffer_head *bh;
        struct omfs_inode *oi;

        bh = omfs_bread(sb, inode->i_ino);
        if (!bh)
                return -ENOMEM;

        memset(bh->b_data, 0, sizeof(struct omfs_inode));

        if (S_ISDIR(inode->i_mode)) {
                memset(&bh->b_data[OMFS_DIR_START], 0xff,
                        sbi->s_sys_blocksize - OMFS_DIR_START);
        } else
                omfs_make_empty_table(bh, OMFS_EXTENT_START);

        oi = (struct omfs_inode *) bh->b_data;
        oi->i_head.h_self = cpu_to_be64(inode->i_ino);
        oi->i_sibling = ~cpu_to_be64(0ULL);

        mark_buffer_dirty(bh);
        brelse(bh);
        return 0;
}

static int omfs_add_link(struct dentry *dentry, struct inode *inode)
{
        struct inode *dir = d_inode(dentry->d_parent);
        const char *name = dentry->d_name.name;
        int namelen = dentry->d_name.len;
        struct omfs_inode *oi;
        struct buffer_head *bh;
        u64 block;
        __be64 *entry;
        int ofs;

        /* just prepend to head of queue in proper bucket */
        bh = omfs_get_bucket(dir, name, namelen, &ofs);
        if (!bh)
                goto out;

        entry = (__be64 *) &bh->b_data[ofs];
        block = be64_to_cpu(*entry);
        *entry = cpu_to_be64(inode->i_ino);
        mark_buffer_dirty(bh);
        brelse(bh);

        /* now set the sibling and parent pointers on the new inode */
        bh = omfs_bread(dir->i_sb, inode->i_ino);
        if (!bh)
                goto out;

        oi = (struct omfs_inode *) bh->b_data;
        memcpy(oi->i_name, name, namelen);
        memset(oi->i_name + namelen, 0, OMFS_NAMELEN - namelen);
        oi->i_sibling = cpu_to_be64(block);
        oi->i_parent = cpu_to_be64(dir->i_ino);
        mark_buffer_dirty(bh);
        brelse(bh);

        dir->i_ctime = current_time(dir);

        /* mark affected inodes dirty to rebuild checksums */
        mark_inode_dirty(dir);
        mark_inode_dirty(inode);
        return 0;
out:
        return -ENOMEM;
}

static int omfs_delete_entry(struct dentry *dentry)
{
        struct inode *dir = d_inode(dentry->d_parent);
        struct inode *dirty;
        const char *name = dentry->d_name.name;
        int namelen = dentry->d_name.len;
        struct omfs_inode *oi;
        struct buffer_head *bh, *bh2;
        __be64 *entry, next;
        u64 block, prev;
        int ofs;
        int err = -ENOMEM;

        /* delete the proper node in the bucket's linked list */
        bh = omfs_get_bucket(dir, name, namelen, &ofs);
        if (!bh)
                goto out;

        entry = (__be64 *) &bh->b_data[ofs];
        block = be64_to_cpu(*entry);

        bh2 = omfs_scan_list(dir, block, name, namelen, &prev);
        if (IS_ERR(bh2)) {
                err = PTR_ERR(bh2);
                goto out_free_bh;
        }

        oi = (struct omfs_inode *) bh2->b_data;
        next = oi->i_sibling;
        brelse(bh2);

        if (prev != ~0) {
                /* found in middle of list, get list ptr */
                brelse(bh);
                bh = omfs_bread(dir->i_sb, prev);
                if (!bh)
                        goto out;

                oi = (struct omfs_inode *) bh->b_data;
                entry = &oi->i_sibling;
        }

        *entry = next;
        mark_buffer_dirty(bh);

        if (prev != ~0) {
                dirty = omfs_iget(dir->i_sb, prev);
                if (!IS_ERR(dirty)) {
                        mark_inode_dirty(dirty);
                        iput(dirty);
                }
        }

        err = 0;
out_free_bh:
        brelse(bh);
out:
        return err;
}

static int omfs_dir_is_empty(struct inode *inode)
{
        int nbuckets = (inode->i_size - OMFS_DIR_START) / 8;
        struct buffer_head *bh;
        u64 *ptr;
        int i;

        bh = omfs_bread(inode->i_sb, inode->i_ino);

        if (!bh)
                return 0;

        ptr = (u64 *) &bh->b_data[OMFS_DIR_START];

        for (i = 0; i < nbuckets; i++, ptr++)
                if (*ptr != ~0)
                        break;

        brelse(bh);
        return *ptr != ~0;
}

static int omfs_remove(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        int ret;


        if (S_ISDIR(inode->i_mode) &&
            !omfs_dir_is_empty(inode))
                return -ENOTEMPTY;

        ret = omfs_delete_entry(dentry);
        if (ret)
                return ret;
        
        clear_nlink(inode);
        mark_inode_dirty(inode);
        mark_inode_dirty(dir);
        return 0;
}

static int omfs_add_node(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        int err;
        struct inode *inode = omfs_new_inode(dir, mode);

        if (IS_ERR(inode))
                return PTR_ERR(inode);

        err = omfs_make_empty(inode, dir->i_sb);
        if (err)
                goto out_free_inode;

        err = omfs_add_link(dentry, inode);
        if (err)
                goto out_free_inode;

        d_instantiate(dentry, inode);
        return 0;

out_free_inode:
        iput(inode);
        return err;
}

static int omfs_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
                      struct dentry *dentry, umode_t mode)
{
        return omfs_add_node(dir, dentry, mode | S_IFDIR);
}

static int omfs_create(struct user_namespace *mnt_userns, struct inode *dir,
                       struct dentry *dentry, umode_t mode, bool excl)
{
        return omfs_add_node(dir, dentry, mode | S_IFREG);
}

static struct dentry *omfs_lookup(struct inode *dir, struct dentry *dentry,
                                  unsigned int flags)
{
        struct buffer_head *bh;
        struct inode *inode = NULL;

        if (dentry->d_name.len > OMFS_NAMELEN)
                return ERR_PTR(-ENAMETOOLONG);

        bh = omfs_find_entry(dir, dentry->d_name.name, dentry->d_name.len);
        if (!IS_ERR(bh)) {
                struct omfs_inode *oi = (struct omfs_inode *)bh->b_data;
                ino_t ino = be64_to_cpu(oi->i_head.h_self);
                brelse(bh);
                inode = omfs_iget(dir->i_sb, ino);
        } else if (bh != ERR_PTR(-ENOENT)) {
                inode = ERR_CAST(bh);
        }
        return d_splice_alias(inode, dentry);
}

/* sanity check block's self pointer */
int omfs_is_bad(struct omfs_sb_info *sbi, struct omfs_header *header,
        u64 fsblock)
{
        int is_bad;
        u64 ino = be64_to_cpu(header->h_self);
        is_bad = ((ino != fsblock) || (ino < sbi->s_root_ino) ||
                (ino > sbi->s_num_blocks));

        if (is_bad)
                printk(KERN_WARNING "omfs: bad hash chain detected\n");

        return is_bad;
}

static bool omfs_fill_chain(struct inode *dir, struct dir_context *ctx,
                u64 fsblock, int hindex)
{
        /* follow chain in this bucket */
        while (fsblock != ~0) {
                struct buffer_head *bh = omfs_bread(dir->i_sb, fsblock);
                struct omfs_inode *oi;
                u64 self;
                unsigned char d_type;

                if (!bh)
                        return true;

                oi = (struct omfs_inode *) bh->b_data;
                if (omfs_is_bad(OMFS_SB(dir->i_sb), &oi->i_head, fsblock)) {
                        brelse(bh);
                        return true;
                }

                self = fsblock;
                fsblock = be64_to_cpu(oi->i_sibling);

                /* skip visited nodes */
                if (hindex) {
                        hindex--;
                        brelse(bh);
                        continue;
                }

                d_type = (oi->i_type == OMFS_DIR) ? DT_DIR : DT_REG;

                if (!dir_emit(ctx, oi->i_name,
                              strnlen(oi->i_name, OMFS_NAMELEN),
                              self, d_type)) {
                        brelse(bh);
                        return false;
                }
                brelse(bh);
                ctx->pos++;
        }
        return true;
}

static int omfs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
                       struct dentry *old_dentry, struct inode *new_dir,
                       struct dentry *new_dentry, unsigned int flags)
{
        struct inode *new_inode = d_inode(new_dentry);
        struct inode *old_inode = d_inode(old_dentry);
        int err;

        if (flags & ~RENAME_NOREPLACE)
                return -EINVAL;

        if (new_inode) {
                /* overwriting existing file/dir */
                err = omfs_remove(new_dir, new_dentry);
                if (err)
                        goto out;
        }

        /* since omfs locates files by name, we need to unlink _before_
         * adding the new link or we won't find the old one */
        err = omfs_delete_entry(old_dentry);
        if (err)
                goto out;

        mark_inode_dirty(old_dir);
        err = omfs_add_link(new_dentry, old_inode);
        if (err)
                goto out;

        old_inode->i_ctime = current_time(old_inode);
        mark_inode_dirty(old_inode);
out:
        return err;
}

static int omfs_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *dir = file_inode(file);
        struct buffer_head *bh;
        __be64 *p;
        unsigned int hchain, hindex;
        int nbuckets;

        if (ctx->pos >> 32)
                return -EINVAL;

        if (ctx->pos < 1 << 20) {
                if (!dir_emit_dots(file, ctx))
                        return 0;
                ctx->pos = 1 << 20;
        }

        nbuckets = (dir->i_size - OMFS_DIR_START) / 8;

        /* high 12 bits store bucket + 1 and low 20 bits store hash index */
        hchain = (ctx->pos >> 20) - 1;
        hindex = ctx->pos & 0xfffff;

        bh = omfs_bread(dir->i_sb, dir->i_ino);
        if (!bh)
                return -EINVAL;

        p = (__be64 *)(bh->b_data + OMFS_DIR_START) + hchain;

        for (; hchain < nbuckets; hchain++) {
                __u64 fsblock = be64_to_cpu(*p++);
                if (!omfs_fill_chain(dir, ctx, fsblock, hindex))
                        break;
                hindex = 0;
                ctx->pos = (hchain+2) << 20;
        }
        brelse(bh);
        return 0;
}

const struct inode_operations omfs_dir_inops = {
        .lookup = omfs_lookup,
        .mkdir = omfs_mkdir,
        .rename = omfs_rename,
        .create = omfs_create,
        .unlink = omfs_remove,
        .rmdir = omfs_remove,
};

const struct file_operations omfs_dir_operations = {
        .read = generic_read_dir,
        .iterate_shared = omfs_readdir,
        .llseek = generic_file_llseek,
};