of: overlay: Add DT-Overlay configfs interface (v7)

Add a runtime interface to using configfs for generic device tree overlay
usage. With it its possible to use device tree overlays without having
to use a per-platform overlay manager.

Please see Documentation/devicetree/configfs-overlays.txt for more info.

Changes since v6:
- Default groups properties API changed.

Changes since v5:
- New style configfs.

Changes since v4:
- Loading fix for multiple overlays as found out by
  Geert Uytterhoeven <geert@linux-m68k.org>

Changes since v3:
- Fixed compilation on SPARC & Xtensa

Changes since v2:
- Removed ifdef CONFIG_OF_OVERLAY (since for now it's required)
- Created a documentation entry
- Slight rewording in Kconfig

Changes since v1:
- of_resolve() -> of_resolve_phandles().

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
[geert: Use %zu to format size_t]
[geert: Rebase to v4.15-rc1]
[geert: Make cfs_overlay_item_dtbo_{read,write}() and of_cfs_overlay_group static]
[geert: Let OF_CONFIGFS select OF_FLATTREE to fix sparc all*config]
[geert: Spelling/grammar s/rationalle of/rationale for/]
[geert: Rebase on top of commit 39a751a ("of: change overlay apply input data from unflattened to FDT") in v4.17-rc1]
[geert: Unapplied ov_id is zero since commit  067c098 ("of: overlay: rework overlay apply and remove kfree()s") in v5.19]
[geert: Remove partially applied overlay]
[geert: Use %pe]
[geert: Use sysfs_emit()]
[geert: Make less verbose]
[geert: Coding style]
[geert: Rebase on top of commit commit cf60ce9 ("of: overlay: Fix of_overlay_fdt_apply prototype when !CONFIG_OF_OVERLAY") in v6.6-rc1]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Author: pantoniou

Documentation/devicetree/configfs-overlays.txt

@@ -0,0 +1,31 @@
+Howto use the configfs overlay interface.
+
+A device-tree configfs entry is created in /config/device-tree/overlays
+and and it is manipulated using standard file system I/O.
+Note that this is a debug level interface, for use by developers and
+not necessarily something accessed by normal users due to the
+security implications of having direct access to the kernel's device tree.
+
+* To create an overlay you mkdir the directory:
+
+	# mkdir /config/device-tree/overlays/foo
+
+* Either you echo the overlay firmware file to the path property file.
+
+	# echo foo.dtbo >/config/device-tree/overlays/foo/path
+
+* Or you cat the contents of the overlay to the dtbo file
+
+	# cat foo.dtbo >/config/device-tree/overlays/foo/dtbo
+
+The overlay file will be applied, and devices will be created/destroyed
+as required.
+
+To remove it simply rmdir the directory.
+
+	# rmdir /config/device-tree/overlays/foo
+
+The rationale for the dual interface (firmware & direct copy) is that each is
+better suited to different use patterns. The firmware interface is what's
+intended to be used by hardware managers in the kernel, while the copy interface
+make sense for developers (since it avoids problems with namespaces).

drivers/of/Kconfig

@@ -99,6 +99,14 @@ config OF_OVERLAY
 	  While this option is selected automatically when needed, you can
 	  enable it manually to improve device tree unit test coverage.
 
+config OF_CONFIGFS
+	bool "Device Tree Overlay ConfigFS interface"
+	select CONFIGFS_FS
+	select OF_FLATTREE
+	depends on OF_OVERLAY
+	help
+	  Enable a simple user-space driven DT overlay interface.
+
 config OF_NUMA
 	bool
 

drivers/of/Makefile

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-y = base.o cpu.o device.o module.o platform.o property.o
 obj-$(CONFIG_OF_KOBJ) += kobj.o
+obj-$(CONFIG_OF_CONFIGFS) += configfs.o
 obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
 obj-$(CONFIG_OF_FLATTREE) += fdt.o
 obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o

drivers/of/configfs.c

@@ -0,0 +1,286 @@
+/*
+ * Configfs entries for device-tree
+ *
+ * Copyright (C) 2013 - Pantelis Antoniou <panto@antoniou-consulting.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <linux/ctype.h>
+#include <linux/cpu.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+#include <linux/spinlock.h>
+#include <linux/sizes.h>
+#include <linux/slab.h>
+#include <linux/proc_fs.h>
+#include <linux/configfs.h>
+#include <linux/types.h>
+#include <linux/stat.h>
+#include <linux/limits.h>
+#include <linux/file.h>
+#include <linux/vmalloc.h>
+#include <linux/firmware.h>
+
+#include "of_private.h"
+
+struct cfs_overlay_item {
+	struct config_item	item;
+
+	char			path[PATH_MAX];
+
+	const struct firmware	*fw;
+	struct device_node	*overlay;
+	int			ov_id;
+
+	void			*dtbo;
+	int			dtbo_size;
+};
+
+static int create_overlay(struct cfs_overlay_item *overlay, const void *blob,
+			  size_t size)
+{
+	int err, err2;
+
+	err = of_overlay_fdt_apply(blob, size, &overlay->ov_id, NULL);
+	if (err < 0) {
+		pr_err("%s: Failed to apply overlay: %pe\n", __func__,
+		       ERR_PTR(err));
+
+		/* changeset may be partially applied */
+		err2 = of_overlay_remove(&overlay->ov_id);
+		if (err2 < 0)
+			pr_err("%s: Failed to remove failed overlay: %pe\n",
+			       __func__, ERR_PTR(err2));
+	}
+
+	return err;
+}
+
+static inline struct cfs_overlay_item *to_cfs_overlay_item(
+		struct config_item *item)
+{
+	return item ? container_of(item, struct cfs_overlay_item, item) : NULL;
+}
+
+static ssize_t cfs_overlay_item_path_show(struct config_item *item, char *buf)
+{
+	return sysfs_emit(buf, "%s\n", to_cfs_overlay_item(item)->path);
+}
+
+static ssize_t cfs_overlay_item_path_store(struct config_item *item,
+		const char *buf, size_t count)
+{
+	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
+	const char *p = buf;
+	char *s;
+	int err;
+
+	/* if it's set do not allow changes */
+	if (overlay->path[0] || overlay->dtbo_size > 0)
+		return -EPERM;
+
+	/* copy to path buffer (and make sure it's always zero terminated */
+	count = snprintf(overlay->path, sizeof(overlay->path) - 1, "%s", p);
+	overlay->path[sizeof(overlay->path) - 1] = '\0';
+
+	/* strip trailing newlines */
+	s = overlay->path + strlen(overlay->path);
+	while (s > overlay->path && *--s == '\n')
+		*s = '\0';
+
+	pr_debug("%s: path is '%s'\n", __func__, overlay->path);
+
+	err = request_firmware(&overlay->fw, overlay->path, NULL);
+	if (err)
+		goto out_err;
+
+	err = create_overlay(overlay, overlay->fw->data, overlay->fw->size);
+	if (err < 0)
+		goto out_err;
+
+	return count;
+
+out_err:
+	release_firmware(overlay->fw);
+	overlay->fw = NULL;
+
+	overlay->path[0] = '\0';
+	return err;
+}
+
+static ssize_t cfs_overlay_item_status_show(struct config_item *item,
+					    char *buf)
+{
+	return sysfs_emit(buf, "%sapplied\n",
+			  to_cfs_overlay_item(item)->ov_id > 0 ? "" : "un");
+}
+
+CONFIGFS_ATTR(cfs_overlay_item_, path);
+CONFIGFS_ATTR_RO(cfs_overlay_item_, status);
+
+static struct configfs_attribute *cfs_overlay_attrs[] = {
+	&cfs_overlay_item_attr_path,
+	&cfs_overlay_item_attr_status,
+	NULL,
+};
+
+static ssize_t cfs_overlay_item_dtbo_read(struct config_item *item, void *buf,
+		size_t max_count)
+{
+	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
+
+	pr_debug("%s: buf=%p max_count=%zu\n", __func__,
+			buf, max_count);
+
+	if (overlay->dtbo == NULL)
+		return 0;
+
+	/* copy if buffer provided */
+	if (buf) {
+		/* the buffer must be large enough */
+		if (overlay->dtbo_size > max_count)
+			return -ENOSPC;
+
+		memcpy(buf, overlay->dtbo, overlay->dtbo_size);
+	}
+
+	return overlay->dtbo_size;
+}
+
+static ssize_t cfs_overlay_item_dtbo_write(struct config_item *item,
+		const void *buf, size_t count)
+{
+	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
+	int err;
+
+	/* if it's set do not allow changes */
+	if (overlay->path[0] || overlay->dtbo_size > 0)
+		return -EPERM;
+
+	/* copy the contents */
+	overlay->dtbo = kmemdup(buf, count, GFP_KERNEL);
+	if (overlay->dtbo == NULL)
+		return -ENOMEM;
+
+	overlay->dtbo_size = count;
+
+	err = create_overlay(overlay, overlay->dtbo, overlay->dtbo_size);
+	if (err < 0)
+		goto out_err;
+
+	return count;
+
+out_err:
+	kfree(overlay->dtbo);
+	overlay->dtbo = NULL;
+	overlay->dtbo_size = 0;
+
+	return err;
+}
+
+CONFIGFS_BIN_ATTR(cfs_overlay_item_, dtbo, NULL, SZ_1M);
+
+static struct configfs_bin_attribute *cfs_overlay_bin_attrs[] = {
+	&cfs_overlay_item_attr_dtbo,
+	NULL,
+};
+
+static void cfs_overlay_release(struct config_item *item)
+{
+	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
+
+	if (overlay->ov_id > 0)
+		of_overlay_remove(&overlay->ov_id);
+	if (overlay->fw)
+		release_firmware(overlay->fw);
+
+	/* kfree with NULL is safe */
+	kfree(overlay->dtbo);
+	kfree(overlay);
+}
+
+static struct configfs_item_operations cfs_overlay_item_ops = {
+	.release		= cfs_overlay_release,
+};
+
+static struct config_item_type cfs_overlay_type = {
+	.ct_item_ops	= &cfs_overlay_item_ops,
+	.ct_attrs	= cfs_overlay_attrs,
+	.ct_bin_attrs	= cfs_overlay_bin_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_item *cfs_overlay_group_make_item(
+		struct config_group *group, const char *name)
+{
+	struct cfs_overlay_item *overlay;
+
+	overlay = kzalloc(sizeof(*overlay), GFP_KERNEL);
+	if (!overlay)
+		return ERR_PTR(-ENOMEM);
+
+	config_item_init_type_name(&overlay->item, name, &cfs_overlay_type);
+	return &overlay->item;
+}
+
+static void cfs_overlay_group_drop_item(struct config_group *group,
+		struct config_item *item)
+{
+	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
+
+	config_item_put(&overlay->item);
+}
+
+static struct configfs_group_operations overlays_ops = {
+	.make_item	= cfs_overlay_group_make_item,
+	.drop_item	= cfs_overlay_group_drop_item,
+};
+
+static struct config_item_type overlays_type = {
+	.ct_group_ops   = &overlays_ops,
+	.ct_owner       = THIS_MODULE,
+};
+
+static struct configfs_group_operations of_cfs_ops = {
+	/* empty - we don't allow anything to be created */
+};
+
+static struct config_item_type of_cfs_type = {
+	.ct_group_ops   = &of_cfs_ops,
+	.ct_owner       = THIS_MODULE,
+};
+
+static struct config_group of_cfs_overlay_group;
+
+static struct configfs_subsystem of_cfs_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = "device-tree",
+			.ci_type = &of_cfs_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(of_cfs_subsys.su_mutex),
+};
+
+static int __init of_cfs_init(void)
+{
+	int ret;
+
+	config_group_init(&of_cfs_subsys.su_group);
+	config_group_init_type_name(&of_cfs_overlay_group, "overlays",
+				    &overlays_type);
+	configfs_add_default_group(&of_cfs_overlay_group,
+				   &of_cfs_subsys.su_group);
+
+	ret = configfs_register_subsystem(&of_cfs_subsys);
+	if (ret)
+		pr_err("%s: Failed to register subsys: %pe\n", __func__,
+		       ERR_PTR(ret));
+
+	return ret;
+}
+late_initcall(of_cfs_init);