// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/adfs/dir_f.c
 *
 * Copyright (C) 1997-1999 Russell King
 *
 *  E and F format directory handling
 */
#include "adfs.h"
#include "dir_f.h"

/*
 * Read an (unaligned) value of length 1..4 bytes
 */
static inline unsigned int adfs_readval(unsigned char *p, int len)
{
        unsigned int val = 0;

        switch (len) {
        case 4:         val |= p[3] << 24;
                fallthrough;
        case 3:         val |= p[2] << 16;
                fallthrough;
        case 2:         val |= p[1] << 8;
                fallthrough;
        default:        val |= p[0];
        }
        return val;
}

static inline void adfs_writeval(unsigned char *p, int len, unsigned int val)
{
        switch (len) {
        case 4:         p[3] = val >> 24;
                fallthrough;
        case 3:         p[2] = val >> 16;
                fallthrough;
        case 2:         p[1] = val >> 8;
                fallthrough;
        default:        p[0] = val;
        }
}

#define ror13(v) ((v >> 13) | (v << 19))

#define dir_u8(idx)                             \
        ({ int _buf = idx >> blocksize_bits;    \
           int _off = idx - (_buf << blocksize_bits);\
          *(u8 *)(bh[_buf]->b_data + _off);     \
        })

#define dir_u32(idx)                            \
        ({ int _buf = idx >> blocksize_bits;    \
           int _off = idx - (_buf << blocksize_bits);\
          *(__le32 *)(bh[_buf]->b_data + _off); \
        })

#define bufoff(_bh,_idx)                        \
        ({ int _buf = _idx >> blocksize_bits;   \
           int _off = _idx - (_buf << blocksize_bits);\
          (void *)(_bh[_buf]->b_data + _off);   \
        })

/*
 * There are some algorithms that are nice in
 * assembler, but a bitch in C...  This is one
 * of them.
 */
static u8
adfs_dir_checkbyte(const struct adfs_dir *dir)
{
        struct buffer_head * const *bh = dir->bh;
        const int blocksize_bits = dir->sb->s_blocksize_bits;
        union { __le32 *ptr32; u8 *ptr8; } ptr, end;
        u32 dircheck = 0;
        int last = 5 - 26;
        int i = 0;

        /*
         * Accumulate each word up to the last whole
         * word of the last directory entry.  This
         * can spread across several buffer heads.
         */
        do {
                last += 26;
                do {
                        dircheck = le32_to_cpu(dir_u32(i)) ^ ror13(dircheck);

                        i += sizeof(u32);
                } while (i < (last & ~3));
        } while (dir_u8(last) != 0);

        /*
         * Accumulate the last few bytes.  These
         * bytes will be within the same bh.
         */
        if (i != last) {
                ptr.ptr8 = bufoff(bh, i);
                end.ptr8 = ptr.ptr8 + last - i;

                do {
                        dircheck = *ptr.ptr8++ ^ ror13(dircheck);
                } while (ptr.ptr8 < end.ptr8);
        }

        /*
         * The directory tail is in the final bh
         * Note that contary to the RISC OS PRMs,
         * the first few bytes are NOT included
         * in the check.  All bytes are in the
         * same bh.
         */
        ptr.ptr8 = bufoff(bh, 2008);
        end.ptr8 = ptr.ptr8 + 36;

        do {
                __le32 v = *ptr.ptr32++;
                dircheck = le32_to_cpu(v) ^ ror13(dircheck);
        } while (ptr.ptr32 < end.ptr32);

        return (dircheck ^ (dircheck >> 8) ^ (dircheck >> 16) ^ (dircheck >> 24)) & 0xff;
}

static int adfs_f_validate(struct adfs_dir *dir)
{
        struct adfs_dirheader *head = dir->dirhead;
        struct adfs_newdirtail *tail = dir->newtail;

        if (head->startmasseq != tail->endmasseq ||
            tail->dirlastmask || tail->reserved[0] || tail->reserved[1] ||
            (memcmp(&head->startname, "Nick", 4) &&
             memcmp(&head->startname, "Hugo", 4)) ||
            memcmp(&head->startname, &tail->endname, 4) ||
            adfs_dir_checkbyte(dir) != tail->dircheckbyte)
                return -EIO;

        return 0;
}

/* Read and check that a directory is valid */
static int adfs_f_read(struct super_block *sb, u32 indaddr, unsigned int size,
                       struct adfs_dir *dir)
{
        const unsigned int blocksize_bits = sb->s_blocksize_bits;
        int ret;

        if (size && size != ADFS_NEWDIR_SIZE)
                return -EIO;

        ret = adfs_dir_read_buffers(sb, indaddr, ADFS_NEWDIR_SIZE, dir);
        if (ret)
                return ret;

        dir->dirhead = bufoff(dir->bh, 0);
        dir->newtail = bufoff(dir->bh, 2007);

        if (adfs_f_validate(dir))
                goto bad_dir;

        dir->parent_id = adfs_readval(dir->newtail->dirparent, 3);

        return 0;

bad_dir:
        adfs_error(sb, "dir %06x is corrupted", indaddr);
        adfs_dir_relse(dir);

        return -EIO;
}

/*
 * convert a disk-based directory entry to a Linux ADFS directory entry
 */
static inline void
adfs_dir2obj(struct adfs_dir *dir, struct object_info *obj,
        struct adfs_direntry *de)
{
        unsigned int name_len;

        for (name_len = 0; name_len < ADFS_F_NAME_LEN; name_len++) {
                if (de->dirobname[name_len] < ' ')
                        break;

                obj->name[name_len] = de->dirobname[name_len];
        }

        obj->name_len = name_len;
        obj->indaddr  = adfs_readval(de->dirinddiscadd, 3);
        obj->loadaddr = adfs_readval(de->dirload, 4);
        obj->execaddr = adfs_readval(de->direxec, 4);
        obj->size     = adfs_readval(de->dirlen,  4);
        obj->attr     = de->newdiratts;

        adfs_object_fixup(dir, obj);
}

/*
 * convert a Linux ADFS directory entry to a disk-based directory entry
 */
static inline void
adfs_obj2dir(struct adfs_direntry *de, struct object_info *obj)
{
        adfs_writeval(de->dirinddiscadd, 3, obj->indaddr);
        adfs_writeval(de->dirload, 4, obj->loadaddr);
        adfs_writeval(de->direxec, 4, obj->execaddr);
        adfs_writeval(de->dirlen,  4, obj->size);
        de->newdiratts = obj->attr;
}

/*
 * get a directory entry.  Note that the caller is responsible
 * for holding the relevant locks.
 */
static int
__adfs_dir_get(struct adfs_dir *dir, int pos, struct object_info *obj)
{
        struct adfs_direntry de;
        int ret;

        ret = adfs_dir_copyfrom(&de, dir, pos, 26);
        if (ret)
                return ret;

        if (!de.dirobname[0])
                return -ENOENT;

        adfs_dir2obj(dir, obj, &de);

        return 0;
}

static int
adfs_f_setpos(struct adfs_dir *dir, unsigned int fpos)
{
        if (fpos >= ADFS_NUM_DIR_ENTRIES)
                return -ENOENT;

        dir->pos = 5 + fpos * 26;
        return 0;
}

static int
adfs_f_getnext(struct adfs_dir *dir, struct object_info *obj)
{
        unsigned int ret;

        ret = __adfs_dir_get(dir, dir->pos, obj);
        if (ret == 0)
                dir->pos += 26;

        return ret;
}

static int adfs_f_iterate(struct adfs_dir *dir, struct dir_context *ctx)
{
        struct object_info obj;
        int pos = 5 + (ctx->pos - 2) * 26;

        while (ctx->pos < 2 + ADFS_NUM_DIR_ENTRIES) {
                if (__adfs_dir_get(dir, pos, &obj))
                        break;
                if (!dir_emit(ctx, obj.name, obj.name_len,
                              obj.indaddr, DT_UNKNOWN))
                        break;
                pos += 26;
                ctx->pos++;
        }
        return 0;
}

static int adfs_f_update(struct adfs_dir *dir, struct object_info *obj)
{
        struct adfs_direntry de;
        int offset, ret;

        offset = 5 - (int)sizeof(de);

        do {
                offset += sizeof(de);
                ret = adfs_dir_copyfrom(&de, dir, offset, sizeof(de));
                if (ret) {
                        adfs_error(dir->sb, "error reading directory entry");
                        return -ENOENT;
                }
                if (!de.dirobname[0]) {
                        adfs_error(dir->sb, "unable to locate entry to update");
                        return -ENOENT;
                }
        } while (adfs_readval(de.dirinddiscadd, 3) != obj->indaddr);

        /* Update the directory entry with the new object state */
        adfs_obj2dir(&de, obj);

        /* Write the directory entry back to the directory */
        return adfs_dir_copyto(dir, offset, &de, 26);
}

static int adfs_f_commit(struct adfs_dir *dir)
{
        int ret;

        /* Increment directory sequence number */
        dir->dirhead->startmasseq += 1;
        dir->newtail->endmasseq += 1;

        /* Update directory check byte */
        dir->newtail->dircheckbyte = adfs_dir_checkbyte(dir);

        /* Make sure the directory still validates correctly */
        ret = adfs_f_validate(dir);
        if (ret)
                adfs_msg(dir->sb, KERN_ERR, "error: update broke directory");

        return ret;
}

const struct adfs_dir_ops adfs_f_dir_ops = {
        .read           = adfs_f_read,
        .iterate        = adfs_f_iterate,
        .setpos         = adfs_f_setpos,
        .getnext        = adfs_f_getnext,
        .update         = adfs_f_update,
        .commit         = adfs_f_commit,
};