alistair23-linux/drivers/mtd/mtdsuper.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* MTD-based superblock management
 *
 * Copyright © 2001-2007 Red Hat, Inc. All Rights Reserved.
 * Copyright © 2001-2010 David Woodhouse <dwmw2@infradead.org>
 *
 * Written by:  David Howells <dhowells@redhat.com>
 *              David Woodhouse <dwmw2@infradead.org>
 */

#include <linux/mtd/super.h>
#include <linux/namei.h>
#include <linux/export.h>
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/major.h>
#include <linux/backing-dev.h>

/*
 * compare superblocks to see if they're equivalent
 * - they are if the underlying MTD device is the same
 */
static int get_sb_mtd_compare(struct super_block *sb, void *_mtd)
{
	struct mtd_info *mtd = _mtd;

	if (sb->s_mtd == mtd) {
		pr_debug("MTDSB: Match on device %d (\"%s\")\n",
		      mtd->index, mtd->name);
		return 1;
	}

	pr_debug("MTDSB: No match, device %d (\"%s\"), device %d (\"%s\")\n",
	      sb->s_mtd->index, sb->s_mtd->name, mtd->index, mtd->name);
	return 0;
}

extern struct backing_dev_info *mtd_bdi;

/*
 * mark the superblock by the MTD device it is using
 * - set the device number to be the correct MTD block device for pesuperstence
 *   of NFS exports
 */
static int get_sb_mtd_set(struct super_block *sb, void *_mtd)
{
	struct mtd_info *mtd = _mtd;

	sb->s_mtd = mtd;
	sb->s_dev = MKDEV(MTD_BLOCK_MAJOR, mtd->index);
	sb->s_bdi = bdi_get(mtd_bdi);

	return 0;
}

/*
 * get a superblock on an MTD-backed filesystem
 */
static struct dentry *mount_mtd_aux(struct file_system_type *fs_type, int flags,
			  const char *dev_name, void *data,
			  struct mtd_info *mtd,
			  int (*fill_super)(struct super_block *, void *, int))
{
	struct super_block *sb;
	int ret;

	sb = sget(fs_type, get_sb_mtd_compare, get_sb_mtd_set, flags, mtd);
	if (IS_ERR(sb))
		goto out_error;

	if (sb->s_root)
		goto already_mounted;

	/* fresh new superblock */
	pr_debug("MTDSB: New superblock for device %d (\"%s\")\n",
	      mtd->index, mtd->name);

	ret = fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
	if (ret < 0) {
		deactivate_locked_super(sb);
		return ERR_PTR(ret);
	}

	/* go */
	sb->s_flags |= SB_ACTIVE;
	return dget(sb->s_root);

	/* new mountpoint for an already mounted superblock */
already_mounted:
	pr_debug("MTDSB: Device %d (\"%s\") is already mounted\n",
	      mtd->index, mtd->name);
	put_mtd_device(mtd);
	return dget(sb->s_root);

out_error:
	put_mtd_device(mtd);
	return ERR_CAST(sb);
}

/*
 * get a superblock on an MTD-backed filesystem by MTD device number
 */
static struct dentry *mount_mtd_nr(struct file_system_type *fs_type, int flags,
			 const char *dev_name, void *data, int mtdnr,
			 int (*fill_super)(struct super_block *, void *, int))
{
	struct mtd_info *mtd;

	mtd = get_mtd_device(NULL, mtdnr);
	if (IS_ERR(mtd)) {
		pr_debug("MTDSB: Device #%u doesn't appear to exist\n", mtdnr);
		return ERR_CAST(mtd);
	}

	return mount_mtd_aux(fs_type, flags, dev_name, data, mtd, fill_super);
}

/*
 * set up an MTD-based superblock
 */
struct dentry *mount_mtd(struct file_system_type *fs_type, int flags,
	       const char *dev_name, void *data,
	       int (*fill_super)(struct super_block *, void *, int))
{
#ifdef CONFIG_BLOCK
	struct block_device *bdev;
	int ret, major;
#endif
	int mtdnr;

	if (!dev_name)
		return ERR_PTR(-EINVAL);

	pr_debug("MTDSB: dev_name \"%s\"\n", dev_name);

	/* the preferred way of mounting in future; especially when
	 * CONFIG_BLOCK=n - we specify the underlying MTD device by number or
	 * by name, so that we don't require block device support to be present
	 * in the kernel. */
	if (dev_name[0] == 'm' && dev_name[1] == 't' && dev_name[2] == 'd') {
		if (dev_name[3] == ':') {
			struct mtd_info *mtd;

			/* mount by MTD device name */
			pr_debug("MTDSB: mtd:%%s, name \"%s\"\n",
			      dev_name + 4);

			mtd = get_mtd_device_nm(dev_name + 4);
			if (!IS_ERR(mtd))
				return mount_mtd_aux(
					fs_type, flags,
					dev_name, data, mtd,
					fill_super);

			printk(KERN_NOTICE "MTD:"
			       " MTD device with name \"%s\" not found.\n",
			       dev_name + 4);

		} else if (isdigit(dev_name[3])) {
			/* mount by MTD device number name */
			char *endptr;

			mtdnr = simple_strtoul(dev_name + 3, &endptr, 0);
			if (!*endptr) {
				/* It was a valid number */
				pr_debug("MTDSB: mtd%%d, mtdnr %d\n",
				      mtdnr);
				return mount_mtd_nr(fs_type, flags,
						     dev_name, data,
						     mtdnr, fill_super);
			}
		}
	}

#ifdef CONFIG_BLOCK
	/* try the old way - the hack where we allowed users to mount
	 * /dev/mtdblock$(n) but didn't actually _use_ the blockdev
	 */
	bdev = lookup_bdev(dev_name);
	if (IS_ERR(bdev)) {
		ret = PTR_ERR(bdev);
		pr_debug("MTDSB: lookup_bdev() returned %d\n", ret);
		return ERR_PTR(ret);
	}
	pr_debug("MTDSB: lookup_bdev() returned 0\n");

	ret = -EINVAL;

	major = MAJOR(bdev->bd_dev);
	mtdnr = MINOR(bdev->bd_dev);
	bdput(bdev);

	if (major != MTD_BLOCK_MAJOR)
		goto not_an_MTD_device;

	return mount_mtd_nr(fs_type, flags, dev_name, data, mtdnr, fill_super);

not_an_MTD_device:
#endif /* CONFIG_BLOCK */

	if (!(flags & SB_SILENT))
		printk(KERN_NOTICE
		       "MTD: Attempt to mount non-MTD device \"%s\"\n",
		       dev_name);
	return ERR_PTR(-EINVAL);
}

EXPORT_SYMBOL_GPL(mount_mtd);

/*
 * destroy an MTD-based superblock
 */
void kill_mtd_super(struct super_block *sb)
{
	generic_shutdown_super(sb);
	put_mtd_device(sb->s_mtd);
	sb->s_mtd = NULL;
}

EXPORT_SYMBOL_GPL(kill_mtd_super);