From 6173a065cb395d4a9528c4e49810af127db68141 Mon Sep 17 00:00:00 2001
From: Daniel Golle <daniel@makrotopia.org>
Date: Wed, 16 Nov 2022 12:49:52 +0000
Subject: [PATCH 1/2] block: add uImage.FIT subimage block driver

Add a small block driver which exposes filesystem sub-images contained
in U-Boot uImage.FIT images as block devices.

The uImage.FIT image has to be stored directly on a block device or
partition, MTD device or partition, or UBI volume.

The driver is intended for systems using the U-Boot bootloader and
uses the root device hint left by the bootloader (or the user) in
the 'chosen' section of the device-tree.

Example:
/dts-v1/;
/ {
        chosen {
                rootdisk = <&mmc0_part3>;
        };
};

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 MAINTAINERS                 |   6 +
 drivers/block/Kconfig       |  12 +
 drivers/block/Makefile      |   2 +
 drivers/block/fitblk.c      | 658 ++++++++++++++++++++++++++++++++++++
 drivers/block/open          |   4 +
 include/uapi/linux/fitblk.h |  10 +
 6 files changed, 692 insertions(+)
 create mode 100644 drivers/block/fitblk.c
 create mode 100644 drivers/block/open
 create mode 100644 include/uapi/linux/fitblk.h

--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22015,6 +22015,12 @@ F:	Documentation/filesystems/ubifs-authe
 F:	Documentation/filesystems/ubifs.rst
 F:	fs/ubifs/
 
+U-BOOT UIMAGE.FIT PARSER
+M:	Daniel Golle <daniel@makrotopia.org>
+L:	linux-block@vger.kernel.org
+S:	Maintained
+F:	drivers/block/fitblk.c
+
 UBLK USERSPACE BLOCK DRIVER
 M:	Ming Lei <ming.lei@redhat.com>
 L:	linux-block@vger.kernel.org
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -354,6 +354,18 @@ config VIRTIO_BLK
 	  This is the virtual block driver for virtio.  It can be used with
           QEMU based VMMs (like KVM or Xen).  Say Y or M.
 
+config UIMAGE_FIT_BLK
+	bool "uImage.FIT block driver"
+	help
+	  This driver allows using filesystems contained in uImage.FIT images
+	  by mapping them as block devices.
+
+	  It can currently not be built as a module due to libfdt symbols not
+	  being exported.
+
+	  Say Y if you want to mount filesystems sub-images of a uImage.FIT
+	  stored in a block device partition, mtdblock or ubiblock device.
+
 config BLK_DEV_RBD
 	tristate "Rados block device (RBD)"
 	depends on INET && BLOCK
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -39,4 +39,6 @@ obj-$(CONFIG_BLK_DEV_NULL_BLK)	+= null_b
 
 obj-$(CONFIG_BLK_DEV_UBLK)			+= ublk_drv.o
 
+obj-$(CONFIG_UIMAGE_FIT_BLK)	+= fitblk.o
+
 swim_mod-y	:= swim.o swim_asm.o
--- /dev/null
+++ b/drivers/block/fitblk.c
@@ -0,0 +1,658 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * uImage.FIT virtual block device driver.
+ *
+ * Copyright (C) 2023 Daniel Golle
+ * Copyright (C) 2007 Nick Piggin
+ * Copyright (C) 2007 Novell Inc.
+ *
+ * Initially derived from drivers/block/brd.c which is in parts derived from
+ * drivers/block/rd.c, and drivers/block/loop.c, copyright of their respective
+ * owners.
+ *
+ * uImage.FIT headers extracted from Das U-Boot
+ *  (C) Copyright 2008 Semihalf
+ *  (C) Copyright 2000-2005
+ *  Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ */
+
+#include <linux/init.h>
+#include <linux/initrd.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/major.h>
+#include <linux/blkdev.h>
+#include <linux/blkpg.h>
+#include <linux/blk-mq.h>
+#include <linux/ctype.h>
+#include <linux/hdreg.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/of_fdt.h>
+#include <linux/pagemap.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/refcount.h>
+#include <linux/task_work.h>
+#include <linux/types.h>
+#include <linux/libfdt.h>
+#include <linux/mtd/mtd.h>
+#include <linux/root_dev.h>
+#include <uapi/linux/fitblk.h>
+
+#define FIT_DEVICE_PREFIX	"fit"
+
+/* maximum number of pages used for the uImage.FIT index structure */
+#define FIT_MAX_PAGES		1024
+
+/* minimum free sectors to map as read-write "remainder" volume */
+#define MIN_FREE_SECT		16
+
+/* maximum number of mapped loadables */
+#define MAX_FIT_LOADABLES	16
+
+/* constants for uImage.FIT structrure traversal */
+#define FIT_IMAGES_PATH		"/images"
+#define FIT_CONFS_PATH		"/configurations"
+
+/* hash/signature/key node */
+#define FIT_HASH_NODENAME	"hash"
+#define FIT_ALGO_PROP		"algo"
+#define FIT_VALUE_PROP		"value"
+#define FIT_IGNORE_PROP		"uboot-ignore"
+#define FIT_SIG_NODENAME	"signature"
+#define FIT_KEY_REQUIRED	"required"
+#define FIT_KEY_HINT		"key-name-hint"
+
+/* cipher node */
+#define FIT_CIPHER_NODENAME	"cipher"
+#define FIT_ALGO_PROP		"algo"
+
+/* image node */
+#define FIT_DATA_PROP		"data"
+#define FIT_DATA_POSITION_PROP	"data-position"
+#define FIT_DATA_OFFSET_PROP	"data-offset"
+#define FIT_DATA_SIZE_PROP	"data-size"
+#define FIT_TIMESTAMP_PROP	"timestamp"
+#define FIT_DESC_PROP		"description"
+#define FIT_ARCH_PROP		"arch"
+#define FIT_TYPE_PROP		"type"
+#define FIT_OS_PROP		"os"
+#define FIT_COMP_PROP		"compression"
+#define FIT_ENTRY_PROP		"entry"
+#define FIT_LOAD_PROP		"load"
+
+/* configuration node */
+#define FIT_KERNEL_PROP		"kernel"
+#define FIT_FILESYSTEM_PROP	"filesystem"
+#define FIT_RAMDISK_PROP	"ramdisk"
+#define FIT_FDT_PROP		"fdt"
+#define FIT_LOADABLE_PROP	"loadables"
+#define FIT_DEFAULT_PROP	"default"
+#define FIT_SETUP_PROP		"setup"
+#define FIT_FPGA_PROP		"fpga"
+#define FIT_FIRMWARE_PROP	"firmware"
+#define FIT_STANDALONE_PROP	"standalone"
+
+/* fitblk driver data */
+static const char *_fitblk_claim_ptr = "I belong to fitblk";
+static const char *ubootver;
+struct device_node *rootdisk;
+static struct platform_device *pdev;
+static LIST_HEAD(fitblk_devices);
+static DEFINE_MUTEX(devices_mutex);
+refcount_t num_devs;
+
+struct fitblk {
+	struct platform_device	*pdev;
+	struct block_device	*lower_bdev;
+	sector_t		start_sect;
+	struct gendisk		*disk;
+	struct work_struct	remove_work;
+	struct list_head	list;
+	bool			dead;
+};
+
+static int fitblk_open(struct gendisk *disk, fmode_t mode)
+{
+	struct fitblk *fitblk = disk->private_data;
+
+	if (fitblk->dead)
+		return -ENOENT;
+
+	return 0;
+}
+
+static void fitblk_release(struct gendisk *disk)
+{
+	return;
+}
+
+static void fitblk_submit_bio(struct bio *orig_bio)
+{
+	struct bio *bio = orig_bio;
+	struct fitblk *fitblk = bio->bi_bdev->bd_disk->private_data;
+
+	if (fitblk->dead)
+		return;
+
+	/* mangle bio and re-submit */
+	while (bio) {
+		bio->bi_iter.bi_sector += fitblk->start_sect;
+		bio->bi_bdev = fitblk->lower_bdev;
+		bio = bio->bi_next;
+	}
+	submit_bio(orig_bio);
+}
+
+static void fitblk_remove(struct fitblk *fitblk)
+{
+	blk_mark_disk_dead(fitblk->disk);
+	mutex_lock(&devices_mutex);
+	fitblk->dead = true;
+	list_del(&fitblk->list);
+	mutex_unlock(&devices_mutex);
+
+	schedule_work(&fitblk->remove_work);
+}
+
+static int fitblk_ioctl(struct block_device *bdev, fmode_t mode,
+			unsigned int cmd, unsigned long arg)
+{
+	struct fitblk *fitblk = bdev->bd_disk->private_data;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
+	if (fitblk->dead)
+		return -ENOENT;
+
+	switch (cmd) {
+	case FITBLK_RELEASE:
+		fitblk_remove(fitblk);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct block_device_operations fitblk_fops = {
+	.owner		= THIS_MODULE,
+	.ioctl		= fitblk_ioctl,
+	.open		= fitblk_open,
+	.release	= fitblk_release,
+	.submit_bio	= fitblk_submit_bio,
+};
+
+static void fitblk_purge(struct work_struct *work)
+{
+	struct fitblk *fitblk = container_of(work, struct fitblk, remove_work);
+
+	//del_gendisk(fitblk->disk); // causes crash, not doing it doesn't matter
+	refcount_dec(&num_devs);
+	platform_device_del(fitblk->pdev);
+	platform_device_put(fitblk->pdev);
+
+	if (refcount_dec_if_one(&num_devs)) {
+		sysfs_remove_link(&pdev->dev.kobj, "lower_dev");
+		blkdev_put(fitblk->lower_bdev, &_fitblk_claim_ptr);
+	}
+
+	kfree(fitblk);
+}
+
+static int add_fit_subimage_device(struct block_device *lower_bdev,
+				   unsigned int slot, sector_t start_sect,
+				   sector_t nr_sect, bool readonly)
+{
+	struct fitblk *fitblk;
+	struct gendisk *disk;
+	int err;
+
+	mutex_lock(&devices_mutex);
+	if (!refcount_inc_not_zero(&num_devs))
+		return -EBADF;
+
+	fitblk = kzalloc(sizeof(struct fitblk), GFP_KERNEL);
+	if (!fitblk) {
+		err = -ENOMEM;
+		goto out_unlock;
+	}
+
+	fitblk->lower_bdev = lower_bdev;
+	fitblk->start_sect = start_sect;
+	INIT_WORK(&fitblk->remove_work, fitblk_purge);
+
+	disk = blk_alloc_disk(NUMA_NO_NODE);
+	if (!disk) {
+		err = -ENOMEM;
+		goto out_free_fitblk;
+	}
+
+	disk->first_minor = 0;
+	disk->flags = lower_bdev->bd_disk->flags | GENHD_FL_NO_PART;
+	disk->fops = &fitblk_fops;
+	disk->private_data = fitblk;
+	if (readonly) {
+		set_disk_ro(disk, 1);
+		snprintf(disk->disk_name, sizeof(disk->disk_name), FIT_DEVICE_PREFIX "%u", slot);
+	} else {
+		strcpy(disk->disk_name, FIT_DEVICE_PREFIX "rw");
+	}
+
+	set_capacity(disk, nr_sect);
+
+	disk->queue->queue_flags = lower_bdev->bd_disk->queue->queue_flags;
+	memcpy(&disk->queue->limits, &lower_bdev->bd_disk->queue->limits,
+	       sizeof(struct queue_limits));
+
+	fitblk->disk = disk;
+	fitblk->pdev = platform_device_alloc(disk->disk_name, PLATFORM_DEVID_NONE);
+	if (!fitblk->pdev) {
+		err = -ENOMEM;
+		goto out_cleanup_disk;
+	}
+
+	fitblk->pdev->dev.parent = &pdev->dev;
+	err = platform_device_add(fitblk->pdev);
+	if (err)
+		goto out_put_pdev;
+
+	err = device_add_disk(&fitblk->pdev->dev, disk, NULL);
+	if (err)
+		goto out_del_pdev;
+
+	if (!ROOT_DEV)
+		ROOT_DEV = disk->part0->bd_dev;
+
+	list_add_tail(&fitblk->list, &fitblk_devices);
+
+	mutex_unlock(&devices_mutex);
+
+	return 0;
+
+out_del_pdev:
+	platform_device_del(fitblk->pdev);
+out_put_pdev:
+	platform_device_put(fitblk->pdev);
+out_cleanup_disk:
+	put_disk(disk);
+out_free_fitblk:
+	kfree(fitblk);
+out_unlock:
+	refcount_dec(&num_devs);
+	mutex_unlock(&devices_mutex);
+	return err;
+}
+
+static void fitblk_mark_dead(struct block_device *bdev, bool surprise)
+{
+	struct list_head *n, *tmp;
+	struct fitblk *fitblk;
+
+	mutex_lock(&devices_mutex);
+	list_for_each_safe(n, tmp, &fitblk_devices) {
+		fitblk = list_entry(n, struct fitblk, list);
+		if (fitblk->lower_bdev != bdev)
+			continue;
+
+		fitblk->dead = true;
+		list_del(&fitblk->list);
+		/* removal needs to be deferred to avoid deadlock */
+		schedule_work(&fitblk->remove_work);
+	}
+	mutex_unlock(&devices_mutex);
+}
+
+static const struct blk_holder_ops fitblk_hops = {
+	.mark_dead = fitblk_mark_dead,
+};
+
+static int parse_fit_on_dev(struct device *dev)
+{
+	struct block_device *bdev;
+	struct address_space *mapping;
+	struct folio *folio;
+	pgoff_t f_index = 0;
+	size_t bytes_left, bytes_to_copy;
+	void *pre_fit, *fit, *fit_c;
+	u64 dsize, dsectors, imgmaxsect = 0;
+	u32 size, image_pos, image_len;
+	const __be32 *image_offset_be, *image_len_be, *image_pos_be;
+	int ret = 0, node, images, config;
+	const char *image_name, *image_type, *image_description,
+		*config_default, *config_description, *config_loadables;
+	u32 image_name_len, image_type_len, image_description_len,
+		bootconf_len, config_default_len, config_description_len,
+		config_loadables_len;
+	sector_t start_sect, nr_sects;
+	struct device_node *np = NULL;
+	const char *bootconf_c;
+	const char *loadable;
+	char *bootconf = NULL, *bootconf_term;
+	bool found;
+	int loadables_rem_len, loadable_len;
+	u16 loadcnt;
+	unsigned int slot = 0;
+
+	/* Exclusive open the block device to receive holder notifications */
+	bdev = blkdev_get_by_dev(dev->devt, BLK_OPEN_READ, &_fitblk_claim_ptr, &fitblk_hops);
+	if (!bdev)
+		return -ENODEV;
+
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+
+	mapping = bdev->bd_inode->i_mapping;
+
+	/* map first page */
+	folio = read_mapping_folio(mapping, f_index++, NULL);
+	if (IS_ERR(folio)) {
+		ret = PTR_ERR(folio);
+		goto out_blkdev;
+	}
+	pre_fit = folio_address(folio) + offset_in_folio(folio, 0);
+
+	/* uImage.FIT is based on flattened device tree structure */
+	if (fdt_check_header(pre_fit)) {
+		ret = -EINVAL;
+		folio_put(folio);
+		goto out_blkdev;
+	}
+
+	size = fdt_totalsize(pre_fit);
+
+	if (size > PAGE_SIZE * FIT_MAX_PAGES) {
+		ret = -EOPNOTSUPP;
+		folio_put(folio);
+		goto out_blkdev;
+	}
+
+	/* acquire disk size */
+	dsectors = bdev_nr_sectors(bdev);
+	dsize = dsectors << SECTOR_SHIFT;
+
+	/* abort if FIT structure is larger than disk or partition size */
+	if (size >= dsize) {
+		ret = -EFBIG;
+		folio_put(folio);
+		goto out_blkdev;
+	}
+
+	fit = kmalloc(size, GFP_KERNEL);
+	if (!fit) {
+		ret = -ENOMEM;
+		folio_put(folio);
+		goto out_blkdev;
+	}
+
+	bytes_left = size;
+	fit_c = fit;
+	while (bytes_left > 0) {
+		bytes_to_copy = min_t(size_t, bytes_left,
+				     folio_size(folio) - offset_in_folio(folio, 0));
+		memcpy(fit_c, pre_fit, bytes_to_copy);
+		fit_c += bytes_to_copy;
+		bytes_left -= bytes_to_copy;
+		if (bytes_left) {
+			folio_put(folio);
+			folio = read_mapping_folio(mapping, f_index++, NULL);
+			if (IS_ERR(folio)) {
+				ret = PTR_ERR(folio);
+				goto out_blkdev;
+			};
+			pre_fit = folio_address(folio) + offset_in_folio(folio, 0);
+		}
+	}
+	folio_put(folio);
+
+	/* set boot config node name U-Boot may have added to the device tree */
+	np = of_find_node_by_path("/chosen");
+	if (np) {
+		bootconf_c = of_get_property(np, "u-boot,bootconf", &bootconf_len);
+		if (bootconf_c && bootconf_len)
+			bootconf = kmemdup_nul(bootconf_c, bootconf_len, GFP_KERNEL);
+	}
+
+	if (bootconf) {
+		bootconf_term = strchr(bootconf, '#');
+		if (bootconf_term)
+			*bootconf_term = '\0';
+	}
+
+	/* find configuration path in uImage.FIT */
+	config = fdt_path_offset(fit, FIT_CONFS_PATH);
+	if (config < 0) {
+		pr_err("FIT: Cannot find %s node: %d\n",
+			FIT_CONFS_PATH, config);
+		ret = -ENOENT;
+		goto out_bootconf;
+	}
+
+	/* get default configuration node name */
+	config_default =
+		fdt_getprop(fit, config, FIT_DEFAULT_PROP, &config_default_len);
+
+	/* make sure we got either default or selected boot config node name */
+	if (!config_default && !bootconf) {
+		pr_err("FIT: Cannot find default configuration\n");
+		ret = -ENOENT;
+		goto out_bootconf;
+	}
+
+	/* find selected boot config node, fallback on default config node */
+	node = fdt_subnode_offset(fit, config, bootconf ?: config_default);
+	if (node < 0) {
+		pr_err("FIT: Cannot find %s node: %d\n",
+			bootconf ?: config_default, node);
+		ret = -ENOENT;
+		goto out_bootconf;
+	}
+
+	pr_info("FIT: Detected U-Boot %s\n", ubootver);
+
+	/* get selected configuration data */
+	config_description =
+		fdt_getprop(fit, node, FIT_DESC_PROP, &config_description_len);
+	config_loadables = fdt_getprop(fit, node, FIT_LOADABLE_PROP,
+				       &config_loadables_len);
+
+	pr_info("FIT: %s configuration: \"%.*s\"%s%.*s%s\n",
+		bootconf ? "Selected" : "Default",
+		bootconf ? bootconf_len : config_default_len,
+		bootconf ?: config_default,
+		config_description ? " (" : "",
+		config_description ? config_description_len : 0,
+		config_description ?: "",
+		config_description ? ")" : "");
+
+	if (!config_loadables || !config_loadables_len) {
+		pr_err("FIT: No loadables configured in \"%s\"\n",
+			bootconf ?: config_default);
+		ret = -ENOENT;
+		goto out_bootconf;
+	}
+
+	/* get images path in uImage.FIT */
+	images = fdt_path_offset(fit, FIT_IMAGES_PATH);
+	if (images < 0) {
+		pr_err("FIT: Cannot find %s node: %d\n", FIT_IMAGES_PATH, images);
+		ret = -EINVAL;
+		goto out_bootconf;
+	}
+
+	/* iterate over images in uImage.FIT */
+	fdt_for_each_subnode(node, fit, images) {
+		image_name = fdt_get_name(fit, node, &image_name_len);
+		image_type = fdt_getprop(fit, node, FIT_TYPE_PROP, &image_type_len);
+		image_offset_be = fdt_getprop(fit, node, FIT_DATA_OFFSET_PROP, NULL);
+		image_pos_be = fdt_getprop(fit, node, FIT_DATA_POSITION_PROP, NULL);
+		image_len_be = fdt_getprop(fit, node, FIT_DATA_SIZE_PROP, NULL);
+
+		if (!image_name || !image_type || !image_len_be ||
+		    !image_name_len || !image_type_len)
+			continue;
+
+		image_len = be32_to_cpu(*image_len_be);
+		if (!image_len)
+			continue;
+
+		if (image_offset_be)
+			image_pos = be32_to_cpu(*image_offset_be) + size;
+		else if (image_pos_be)
+			image_pos = be32_to_cpu(*image_pos_be);
+		else
+			continue;
+
+		image_description = fdt_getprop(fit, node, FIT_DESC_PROP,
+						&image_description_len);
+
+		pr_info("FIT: %16s sub-image 0x%08x..0x%08x \"%.*s\"%s%.*s%s\n",
+			image_type, image_pos, image_pos + image_len - 1,
+			image_name_len, image_name, image_description ? " (" : "",
+			image_description ? image_description_len : 0,
+			image_description ?: "", image_description ? ") " : "");
+
+		/* only 'filesystem' images should be mapped as partitions */
+		if (strncmp(image_type, FIT_FILESYSTEM_PROP, image_type_len))
+			continue;
+
+		/* check if sub-image is part of configured loadables */
+		found = false;
+		loadable = config_loadables;
+		loadables_rem_len = config_loadables_len;
+		for (loadcnt = 0; loadables_rem_len > 1 &&
+				  loadcnt < MAX_FIT_LOADABLES; ++loadcnt) {
+			loadable_len =
+				strnlen(loadable, loadables_rem_len - 1) + 1;
+			loadables_rem_len -= loadable_len;
+			if (!strncmp(image_name, loadable, loadable_len)) {
+				found = true;
+				break;
+			}
+			loadable += loadable_len;
+		}
+		if (!found)
+			continue;
+
+		if (image_pos % (1 << PAGE_SHIFT)) {
+			dev_err(dev, "FIT: image %.*s start not aligned to page boundaries, skipping\n",
+				image_name_len, image_name);
+			continue;
+		}
+
+		if (image_len % (1 << PAGE_SHIFT)) {
+			dev_err(dev, "FIT: sub-image %.*s end not aligned to page boundaries, skipping\n",
+				image_name_len, image_name);
+			continue;
+		}
+
+		start_sect = image_pos >> SECTOR_SHIFT;
+		nr_sects = image_len >> SECTOR_SHIFT;
+		imgmaxsect = max_t(sector_t, imgmaxsect, start_sect + nr_sects);
+
+		if (start_sect + nr_sects > dsectors) {
+			dev_err(dev, "FIT: sub-image %.*s disk access beyond EOD\n",
+				image_name_len, image_name);
+			continue;
+		}
+
+		if (!slot) {
+			ret = sysfs_create_link_nowarn(&pdev->dev.kobj, bdev_kobj(bdev), "lower_dev");
+			if (ret && ret != -EEXIST)
+				goto out_bootconf;
+
+			ret = 0;
+		}
+
+		add_fit_subimage_device(bdev, slot++, start_sect, nr_sects, true);
+	}
+
+	if (!found || !slot)
+		goto out_bootconf;
+
+	dev_info(dev, "mapped %u uImage.FIT filesystem sub-image%s as /dev/fit%s%u%s\n",
+		 slot, (slot > 1)?"s":"", (slot > 1)?"[0...":"", slot - 1,
+		 (slot > 1)?"]":"");
+
+	/* in case uImage.FIT is stored in a partition, map the remaining space */
+	if (!bdev->bd_read_only && bdev_is_partition(bdev) &&
+	    (imgmaxsect + MIN_FREE_SECT) < dsectors) {
+		add_fit_subimage_device(bdev, slot++, imgmaxsect,
+					dsectors - imgmaxsect, false);
+		dev_info(dev, "mapped remaining space as /dev/fitrw\n");
+	}
+
+out_bootconf:
+	kfree(bootconf);
+	kfree(fit);
+out_blkdev:
+	if (!found || ret)
+		blkdev_put(bdev, &_fitblk_claim_ptr);
+
+	return ret;
+}
+
+static int fitblk_match_of_node(struct device *dev, const void *np)
+{
+	int ret;
+
+	ret = device_match_of_node(dev, np);
+	if (ret)
+		return ret;
+
+	/*
+	 * To match ubiblock and mtdblock devices by their parent ubi
+	 * or mtd device, also consider block device parent
+	 */
+	if (!dev->parent)
+		return 0;
+
+	return device_match_of_node(dev->parent, np);
+}
+
+static int fitblk_probe(struct platform_device *pdev)
+{
+	struct device *dev;
+
+	dev = class_find_device(&block_class, NULL, rootdisk, fitblk_match_of_node);
+	if (!dev)
+		return -EPROBE_DEFER;
+
+	return parse_fit_on_dev(dev);
+}
+
+static struct platform_driver fitblk_driver = {
+	.probe		= fitblk_probe,
+	.driver		= {
+		.name   = "fitblk",
+	},
+};
+
+static int __init fitblk_init(void)
+{
+	/* detect U-Boot firmware */
+	ubootver = of_get_property(of_chosen, "u-boot,version", NULL);
+	if (!ubootver)
+		return 0;
+
+	/* parse 'rootdisk' property phandle */
+	rootdisk = of_parse_phandle(of_chosen, "rootdisk", 0);
+	if (!rootdisk)
+		return 0;
+
+	if (platform_driver_register(&fitblk_driver))
+		return -ENODEV;
+
+	refcount_set(&num_devs, 1);
+	pdev = platform_device_register_simple("fitblk", -1, NULL, 0);
+	if (IS_ERR(pdev))
+		return PTR_ERR(pdev);
+
+	return 0;
+}
+device_initcall(fitblk_init);
--- /dev/null
+++ b/include/uapi/linux/fitblk.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_FITBLK_H
+#define _UAPI_LINUX_FITBLK_H
+
+/*
+ * IOCTL commands --- we will commandeer 0x46 ('F')
+ */
+#define FITBLK_RELEASE             0x4600
+
+#endif /* _UAPI_LINUX_FITBLK_H */
