package: add fitblk util to release /dev/fit* devices

Add minimalistic tool to allow releasing /dev/fit* devices which is
needed on sysupgrade when using the fitblk driver.
The package is hidden in menuconfig, it should only be selected by
adding it to the default package selection of boards using it.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/utils/fitblk/Makefile

@@ -0,0 +1,41 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=fitblk
+PKG_RELEASE:=1
+PKG_LICENSE:=GPL-2.0-only
+PKG_MAINTAINER:=Daniel Golle <daniel@makrotopia.org>
+
+PKG_BUILD_DIR := $(BUILD_DIR)/$(PKG_NAME)
+
+PKG_FLAGS:=nonshared
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/fitblk
+  HIDDEN:=1
+  SECTION:=base
+  CATEGORY:=Base system
+  TITLE:=fitblk firmware release tool
+  DEPENDS:=@LINUX_6_1
+endef
+
+define Package/fitblk/description
+Release uImage.FIT block devices using ioctl.
+endef
+
+define Build/Configure
+endef
+
+define Build/Compile
+	$(MAKE) -C $(PKG_BUILD_DIR) \
+		CC="$(TARGET_CC)" \
+		CFLAGS="$(TARGET_CFLAGS) -Wall -Werror" \
+		LDFLAGS="$(TARGET_LDFLAGS)"
+endef
+
+define Package/fitblk/install
+	$(INSTALL_DIR) $(1)/usr/sbin
+	$(INSTALL_BIN) $(PKG_BUILD_DIR)/fitblk $(1)/usr/sbin/
+endef
+
+$(eval $(call BuildPackage,fitblk))

package/utils/fitblk/src/Makefile

@@ -0,0 +1,7 @@
+all: fitblk
+
+fitblk:
+	$(CC) $(CFLAGS) -o $@ fitblk.c $(LDFLAGS)
+
+clean:
+	rm -f fitblk

package/utils/fitblk/src/fitblk.c

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <stdio.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <linux/fitblk.h>
+
+static int fitblk_release(char *device)
+{
+	int fd, ret;
+
+	fd = open(device, O_RDONLY);
+	if (fd == -1)
+		return errno;
+
+	ret = ioctl(fd, FITBLK_RELEASE, NULL);
+	close(fd);
+
+	if (ret == -1)
+		return errno;
+
+	return 0;
+}
+
+int main(int argc, char *argp[])
+{
+	int ret;
+
+	if (argc != 2) {
+		fprintf(stderr, "Release uImage.FIT sub-image block device\n");
+		fprintf(stderr, "Syntax: %s /dev/fitXXX\n", argp[0]);
+		return -EINVAL;
+	}
+
+	ret = fitblk_release(argp[1]);
+	if (ret)
+		fprintf(stderr, "fitblk: error releasing %s: %s\n", argp[1],
+			strerror(ret));
+	else
+		fprintf(stderr, "fitblk: %s released\n", argp[1]);
+
+	return ret;
+}