// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/fs/minix/dir.c
 *
 *  Copyright (C) 1991, 1992 Linus Torvalds
 *
 *  minix directory handling functions
 *
 *  Updated to filesystem version 3 by Daniel Aragones
 */

#include "minix.h"
#include <linux/buffer_head.h>
#include <linux/highmem.h>
#include <linux/swap.h>

typedef struct minix_dir_entry minix_dirent;
typedef struct minix3_dir_entry minix3_dirent;

static int minix_readdir(struct file *, struct dir_context *);

const struct file_operations minix_dir_operations = {
        .llseek         = generic_file_llseek,
        .read           = generic_read_dir,
        .iterate_shared = minix_readdir,
        .fsync          = generic_file_fsync,
};

static inline void dir_put_page(struct page *page)
{
        kunmap(page);
        put_page(page);
}

/*
 * Return the offset into page `page_nr' of the last valid
 * byte in that page, plus one.
 */
static unsigned
minix_last_byte(struct inode *inode, unsigned long page_nr)
{
        unsigned last_byte = PAGE_SIZE;

        if (page_nr == (inode->i_size >> PAGE_SHIFT))
                last_byte = inode->i_size & (PAGE_SIZE - 1);
        return last_byte;
}

static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
{
        struct address_space *mapping = page->mapping;
        struct inode *dir = mapping->host;
        int err = 0;
        block_write_end(NULL, mapping, pos, len, len, page, NULL);

        if (pos+len > dir->i_size) {
                i_size_write(dir, pos+len);
                mark_inode_dirty(dir);
        }
        if (IS_DIRSYNC(dir))
                err = write_one_page(page);
        else
                unlock_page(page);
        return err;
}

static struct page * dir_get_page(struct inode *dir, unsigned long n)
{
        struct address_space *mapping = dir->i_mapping;
        struct page *page = read_mapping_page(mapping, n, NULL);
        if (!IS_ERR(page))
                kmap(page);
        return page;
}

static inline void *minix_next_entry(void *de, struct minix_sb_info *sbi)
{
        return (void*)((char*)de + sbi->s_dirsize);
}

static int minix_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *inode = file_inode(file);
        struct super_block *sb = inode->i_sb;
        struct minix_sb_info *sbi = minix_sb(sb);
        unsigned chunk_size = sbi->s_dirsize;
        unsigned long npages = dir_pages(inode);
        unsigned long pos = ctx->pos;
        unsigned offset;
        unsigned long n;

        ctx->pos = pos = ALIGN(pos, chunk_size);
        if (pos >= inode->i_size)
                return 0;

        offset = pos & ~PAGE_MASK;
        n = pos >> PAGE_SHIFT;

        for ( ; n < npages; n++, offset = 0) {
                char *p, *kaddr, *limit;
                struct page *page = dir_get_page(inode, n);

                if (IS_ERR(page))
                        continue;
                kaddr = (char *)page_address(page);
                p = kaddr+offset;
                limit = kaddr + minix_last_byte(inode, n) - chunk_size;
                for ( ; p <= limit; p = minix_next_entry(p, sbi)) {
                        const char *name;
                        __u32 inumber;
                        if (sbi->s_version == MINIX_V3) {
                                minix3_dirent *de3 = (minix3_dirent *)p;
                                name = de3->name;
                                inumber = de3->inode;
                        } else {
                                minix_dirent *de = (minix_dirent *)p;
                                name = de->name;
                                inumber = de->inode;
                        }
                        if (inumber) {
                                unsigned l = strnlen(name, sbi->s_namelen);
                                if (!dir_emit(ctx, name, l,
                                              inumber, DT_UNKNOWN)) {
                                        dir_put_page(page);
                                        return 0;
                                }
                        }
                        ctx->pos += chunk_size;
                }
                dir_put_page(page);
        }
        return 0;
}

static inline int namecompare(int len, int maxlen,
        const char * name, const char * buffer)
{
        if (len < maxlen && buffer[len])
                return 0;
        return !memcmp(name, buffer, len);
}

/*
 *      minix_find_entry()
 *
 * finds an entry in the specified directory with the wanted name. It
 * returns the cache buffer in which the entry was found, and the entry
 * itself (as a parameter - res_dir). It does NOT read the inode of the
 * entry - you'll have to do that yourself if you want to.
 */
minix_dirent *minix_find_entry(struct dentry *dentry, struct page **res_page)
{
        const char * name = dentry->d_name.name;
        int namelen = dentry->d_name.len;
        struct inode * dir = d_inode(dentry->d_parent);
        struct super_block * sb = dir->i_sb;
        struct minix_sb_info * sbi = minix_sb(sb);
        unsigned long n;
        unsigned long npages = dir_pages(dir);
        struct page *page = NULL;
        char *p;

        char *namx;
        __u32 inumber;
        *res_page = NULL;

        for (n = 0; n < npages; n++) {
                char *kaddr, *limit;

                page = dir_get_page(dir, n);
                if (IS_ERR(page))
                        continue;

                kaddr = (char*)page_address(page);
                limit = kaddr + minix_last_byte(dir, n) - sbi->s_dirsize;
                for (p = kaddr; p <= limit; p = minix_next_entry(p, sbi)) {
                        if (sbi->s_version == MINIX_V3) {
                                minix3_dirent *de3 = (minix3_dirent *)p;
                                namx = de3->name;
                                inumber = de3->inode;
                        } else {
                                minix_dirent *de = (minix_dirent *)p;
                                namx = de->name;
                                inumber = de->inode;
                        }
                        if (!inumber)
                                continue;
                        if (namecompare(namelen, sbi->s_namelen, name, namx))
                                goto found;
                }
                dir_put_page(page);
        }
        return NULL;

found:
        *res_page = page;
        return (minix_dirent *)p;
}

int minix_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 super_block * sb = dir->i_sb;
        struct minix_sb_info * sbi = minix_sb(sb);
        struct page *page = NULL;
        unsigned long npages = dir_pages(dir);
        unsigned long n;
        char *kaddr, *p;
        minix_dirent *de;
        minix3_dirent *de3;
        loff_t pos;
        int err;
        char *namx = NULL;
        __u32 inumber;

        /*
         * We take care of directory expansion in the same loop
         * This code plays outside i_size, so it locks the page
         * to protect that region.
         */
        for (n = 0; n <= npages; n++) {
                char *limit, *dir_end;

                page = dir_get_page(dir, n);
                err = PTR_ERR(page);
                if (IS_ERR(page))
                        goto out;
                lock_page(page);
                kaddr = (char*)page_address(page);
                dir_end = kaddr + minix_last_byte(dir, n);
                limit = kaddr + PAGE_SIZE - sbi->s_dirsize;
                for (p = kaddr; p <= limit; p = minix_next_entry(p, sbi)) {
                        de = (minix_dirent *)p;
                        de3 = (minix3_dirent *)p;
                        if (sbi->s_version == MINIX_V3) {
                                namx = de3->name;
                                inumber = de3->inode;
                        } else {
                                namx = de->name;
                                inumber = de->inode;
                        }
                        if (p == dir_end) {
                                /* We hit i_size */
                                if (sbi->s_version == MINIX_V3)
                                        de3->inode = 0;
                                else
                                        de->inode = 0;
                                goto got_it;
                        }
                        if (!inumber)
                                goto got_it;
                        err = -EEXIST;
                        if (namecompare(namelen, sbi->s_namelen, name, namx))
                                goto out_unlock;
                }
                unlock_page(page);
                dir_put_page(page);
        }
        BUG();
        return -EINVAL;

got_it:
        pos = page_offset(page) + p - (char *)page_address(page);
        err = minix_prepare_chunk(page, pos, sbi->s_dirsize);
        if (err)
                goto out_unlock;
        memcpy (namx, name, namelen);
        if (sbi->s_version == MINIX_V3) {
                memset (namx + namelen, 0, sbi->s_dirsize - namelen - 4);
                de3->inode = inode->i_ino;
        } else {
                memset (namx + namelen, 0, sbi->s_dirsize - namelen - 2);
                de->inode = inode->i_ino;
        }
        err = dir_commit_chunk(page, pos, sbi->s_dirsize);
        dir->i_mtime = dir->i_ctime = current_time(dir);
        mark_inode_dirty(dir);
out_put:
        dir_put_page(page);
out:
        return err;
out_unlock:
        unlock_page(page);
        goto out_put;
}

int minix_delete_entry(struct minix_dir_entry *de, struct page *page)
{
        struct inode *inode = page->mapping->host;
        char *kaddr = page_address(page);
        loff_t pos = page_offset(page) + (char*)de - kaddr;
        struct minix_sb_info *sbi = minix_sb(inode->i_sb);
        unsigned len = sbi->s_dirsize;
        int err;

        lock_page(page);
        err = minix_prepare_chunk(page, pos, len);
        if (err == 0) {
                if (sbi->s_version == MINIX_V3)
                        ((minix3_dirent *) de)->inode = 0;
                else
                        de->inode = 0;
                err = dir_commit_chunk(page, pos, len);
        } else {
                unlock_page(page);
        }
        dir_put_page(page);
        inode->i_ctime = inode->i_mtime = current_time(inode);
        mark_inode_dirty(inode);
        return err;
}

int minix_make_empty(struct inode *inode, struct inode *dir)
{
        struct page *page = grab_cache_page(inode->i_mapping, 0);
        struct minix_sb_info *sbi = minix_sb(inode->i_sb);
        char *kaddr;
        int err;

        if (!page)
                return -ENOMEM;
        err = minix_prepare_chunk(page, 0, 2 * sbi->s_dirsize);
        if (err) {
                unlock_page(page);
                goto fail;
        }

        kaddr = kmap_atomic(page);
        memset(kaddr, 0, PAGE_SIZE);

        if (sbi->s_version == MINIX_V3) {
                minix3_dirent *de3 = (minix3_dirent *)kaddr;

                de3->inode = inode->i_ino;
                strcpy(de3->name, ".");
                de3 = minix_next_entry(de3, sbi);
                de3->inode = dir->i_ino;
                strcpy(de3->name, "..");
        } else {
                minix_dirent *de = (minix_dirent *)kaddr;

                de->inode = inode->i_ino;
                strcpy(de->name, ".");
                de = minix_next_entry(de, sbi);
                de->inode = dir->i_ino;
                strcpy(de->name, "..");
        }
        kunmap_atomic(kaddr);

        err = dir_commit_chunk(page, 0, 2 * sbi->s_dirsize);
fail:
        put_page(page);
        return err;
}

/*
 * routine to check that the specified directory is empty (for rmdir)
 */
int minix_empty_dir(struct inode * inode)
{
        struct page *page = NULL;
        unsigned long i, npages = dir_pages(inode);
        struct minix_sb_info *sbi = minix_sb(inode->i_sb);
        char *name;
        __u32 inumber;

        for (i = 0; i < npages; i++) {
                char *p, *kaddr, *limit;

                page = dir_get_page(inode, i);
                if (IS_ERR(page))
                        continue;

                kaddr = (char *)page_address(page);
                limit = kaddr + minix_last_byte(inode, i) - sbi->s_dirsize;
                for (p = kaddr; p <= limit; p = minix_next_entry(p, sbi)) {
                        if (sbi->s_version == MINIX_V3) {
                                minix3_dirent *de3 = (minix3_dirent *)p;
                                name = de3->name;
                                inumber = de3->inode;
                        } else {
                                minix_dirent *de = (minix_dirent *)p;
                                name = de->name;
                                inumber = de->inode;
                        }

                        if (inumber != 0) {
                                /* check for . and .. */
                                if (name[0] != '.')
                                        goto not_empty;
                                if (!name[1]) {
                                        if (inumber != inode->i_ino)
                                                goto not_empty;
                                } else if (name[1] != '.')
                                        goto not_empty;
                                else if (name[2])
                                        goto not_empty;
                        }
                }
                dir_put_page(page);
        }
        return 1;

not_empty:
        dir_put_page(page);
        return 0;
}

/* Releases the page */
void minix_set_link(struct minix_dir_entry *de, struct page *page,
        struct inode *inode)
{
        struct inode *dir = page->mapping->host;
        struct minix_sb_info *sbi = minix_sb(dir->i_sb);
        loff_t pos = page_offset(page) +
                        (char *)de-(char*)page_address(page);
        int err;

        lock_page(page);

        err = minix_prepare_chunk(page, pos, sbi->s_dirsize);
        if (err == 0) {
                if (sbi->s_version == MINIX_V3)
                        ((minix3_dirent *) de)->inode = inode->i_ino;
                else
                        de->inode = inode->i_ino;
                err = dir_commit_chunk(page, pos, sbi->s_dirsize);
        } else {
                unlock_page(page);
        }
        dir_put_page(page);
        dir->i_mtime = dir->i_ctime = current_time(dir);
        mark_inode_dirty(dir);
}

struct minix_dir_entry * minix_dotdot (struct inode *dir, struct page **p)
{
        struct page *page = dir_get_page(dir, 0);
        struct minix_sb_info *sbi = minix_sb(dir->i_sb);
        struct minix_dir_entry *de = NULL;

        if (!IS_ERR(page)) {
                de = minix_next_entry(page_address(page), sbi);
                *p = page;
        }
        return de;
}

ino_t minix_inode_by_name(struct dentry *dentry)
{
        struct page *page;
        struct minix_dir_entry *de = minix_find_entry(dentry, &page);
        ino_t res = 0;

        if (de) {
                struct address_space *mapping = page->mapping;
                struct inode *inode = mapping->host;
                struct minix_sb_info *sbi = minix_sb(inode->i_sb);

                if (sbi->s_version == MINIX_V3)
                        res = ((minix3_dirent *) de)->inode;
                else
                        res = de->inode;
                dir_put_page(page);
        }
        return res;
}