/*
 * Resizable simple ram filesystem for Linux.
 *
 * Copyright (C) 2000 Linus Torvalds.
 *               2000 Transmeta Corp.
 *
 * Usage limits added by David Gibson, Linuxcare Australia.
 * This file is released under the GPL.
 */

/*
 * NOTE! This filesystem is probably most useful
 * not as a real filesystem, but as an example of
 * how virtual filesystems can be written.
 *
 * It doesn't get much simpler than this. Consider
 * that this file implements the full semantics of
 * a POSIX-compliant read-write filesystem.
 *
 * Note in particular how the filesystem does not
 * need to implement any data structures of its own
 * to keep track of the virtual data: using the VFS
 * caches is sufficient.
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/ramfs.h>
#include <linux/sched.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
#include "internal.h"

struct ramfs_mount_opts {
        umode_t mode;
};

struct ramfs_fs_info {
        struct ramfs_mount_opts mount_opts;
};

#define RAMFS_DEFAULT_MODE      0755

static const struct super_operations ramfs_ops;
static const struct inode_operations ramfs_dir_inode_operations;

static const struct address_space_operations ramfs_aops = {
        .readpage       = simple_readpage,
        .write_begin    = simple_write_begin,
        .write_end      = simple_write_end,
        .set_page_dirty = __set_page_dirty_no_writeback,
};

struct inode *ramfs_get_inode(struct super_block *sb,
                                const struct inode *dir, umode_t mode, dev_t dev)
{
        struct inode * inode = new_inode(sb);

        if (inode) {
                inode->i_ino = get_next_ino();
                inode_init_owner(inode, dir, mode);
                inode->i_mapping->a_ops = &ramfs_aops;
                mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
                mapping_set_unevictable(inode->i_mapping);
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
                switch (mode & S_IFMT) {
                default:
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_op = &ramfs_file_inode_operations;
                        inode->i_fop = &ramfs_file_operations;
                        break;
                case S_IFDIR:
                        inode->i_op = &ramfs_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;

                        /* directory inodes start off with i_nlink == 2 (for "." entry) */
                        inc_nlink(inode);
                        break;
                case S_IFLNK:
                        inode->i_op = &page_symlink_inode_operations;
                        inode_nohighmem(inode);
                        break;
                }
        }
        return inode;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
/* SMP-safe */
static int
ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
{
        struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
        int error = -ENOSPC;

        if (inode) {
                d_instantiate(dentry, inode);
                dget(dentry);   /* Extra count - pin the dentry in core */
                error = 0;
                dir->i_mtime = dir->i_ctime = current_time(dir);
        }
        return error;
}

static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
{
        int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
        if (!retval)
                inc_nlink(dir);
        return retval;
}

static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
{
        return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
}

static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
{
        struct inode *inode;
        int error = -ENOSPC;

        inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
        if (inode) {
                int l = strlen(symname)+1;
                error = page_symlink(inode, symname, l);
                if (!error) {
                        d_instantiate(dentry, inode);
                        dget(dentry);
                        dir->i_mtime = dir->i_ctime = current_time(dir);
                } else
                        iput(inode);
        }
        return error;
}

static const struct inode_operations ramfs_dir_inode_operations = {
        .create         = ramfs_create,
        .lookup         = simple_lookup,
        .link           = simple_link,
        .unlink         = simple_unlink,
        .symlink        = ramfs_symlink,
        .mkdir          = ramfs_mkdir,
        .rmdir          = simple_rmdir,
        .mknod          = ramfs_mknod,
        .rename         = simple_rename,
};

/*
 * Display the mount options in /proc/mounts.
 */
static int ramfs_show_options(struct seq_file *m, struct dentry *root)
{
        struct ramfs_fs_info *fsi = root->d_sb->s_fs_info;

        if (fsi->mount_opts.mode != RAMFS_DEFAULT_MODE)
                seq_printf(m, ",mode=%o", fsi->mount_opts.mode);
        return 0;
}

static const struct super_operations ramfs_ops = {
        .statfs         = simple_statfs,
        .drop_inode     = generic_delete_inode,
        .show_options   = ramfs_show_options,
};

enum ramfs_param {
        Opt_mode,
};

const struct fs_parameter_spec ramfs_fs_parameters[] = {
        fsparam_u32oct("mode",  Opt_mode),
        {}
};

static int ramfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct fs_parse_result result;
        struct ramfs_fs_info *fsi = fc->s_fs_info;
        int opt;

        opt = fs_parse(fc, ramfs_fs_parameters, param, &result);
        if (opt < 0) {
                /*
                 * We might like to report bad mount options here;
                 * but traditionally ramfs has ignored all mount options,
                 * and as it is used as a !CONFIG_SHMEM simple substitute
                 * for tmpfs, better continue to ignore other mount options.
                 */
                if (opt == -ENOPARAM)
                        opt = 0;
                return opt;
        }

        switch (opt) {
        case Opt_mode:
                fsi->mount_opts.mode = result.uint_32 & S_IALLUGO;
                break;
        }

        return 0;
}

static int ramfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
        struct ramfs_fs_info *fsi = sb->s_fs_info;
        struct inode *inode;

        sb->s_maxbytes          = MAX_LFS_FILESIZE;
        sb->s_blocksize         = PAGE_SIZE;
        sb->s_blocksize_bits    = PAGE_SHIFT;
        sb->s_magic             = RAMFS_MAGIC;
        sb->s_op                = &ramfs_ops;
        sb->s_time_gran         = 1;

        inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
        sb->s_root = d_make_root(inode);
        if (!sb->s_root)
                return -ENOMEM;

        return 0;
}

static int ramfs_get_tree(struct fs_context *fc)
{
        return get_tree_nodev(fc, ramfs_fill_super);
}

static void ramfs_free_fc(struct fs_context *fc)
{
        kfree(fc->s_fs_info);
}

static const struct fs_context_operations ramfs_context_ops = {
        .free           = ramfs_free_fc,
        .parse_param    = ramfs_parse_param,
        .get_tree       = ramfs_get_tree,
};

int ramfs_init_fs_context(struct fs_context *fc)
{
        struct ramfs_fs_info *fsi;

        fsi = kzalloc(sizeof(*fsi), GFP_KERNEL);
        if (!fsi)
                return -ENOMEM;

        fsi->mount_opts.mode = RAMFS_DEFAULT_MODE;
        fc->s_fs_info = fsi;
        fc->ops = &ramfs_context_ops;
        return 0;
}

static void ramfs_kill_sb(struct super_block *sb)
{
        kfree(sb->s_fs_info);
        kill_litter_super(sb);
}

static struct file_system_type ramfs_fs_type = {
        .name           = "ramfs",
        .init_fs_context = ramfs_init_fs_context,
        .parameters     = ramfs_fs_parameters,
        .kill_sb        = ramfs_kill_sb,
        .fs_flags       = FS_USERNS_MOUNT,
};

static int __init init_ramfs_fs(void)
{
        return register_filesystem(&ramfs_fs_type);
}
fs_initcall(init_ramfs_fs);