configure: Fix compilation on the older kernels

configure.d/1_ida_alloc.conf

@@ -0,0 +1,56 @@
+#!/bin/bash
+#
+# Copyright(c) 2026 Unvertical
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+. $(dirname $3)/conf_framework.sh
+
+# ida_alloc_max()/ida_free() were introduced in v4.19; older kernels only
+# have ida_simple_get()/ida_simple_remove(), which were removed in v6.9.
+check() {
+	cur_name=$(basename $2)
+	config_file_path=$1
+	if compile_module $cur_name "ida_alloc_max(NULL, 0, GFP_KERNEL);" "linux/idr.h"
+	then
+		echo $cur_name "1" >> $config_file_path
+	elif compile_module $cur_name "ida_simple_get(NULL, 0, 0, GFP_KERNEL);" "linux/idr.h"
+	then
+		echo $cur_name "2" >> $config_file_path
+	else
+		echo $cur_name "X" >> $config_file_path
+	fi
+}
+
+apply() {
+    case "$1" in
+    "1")
+		add_function "
+	static inline int cas_ida_alloc_max(struct ida *ida, unsigned int max,
+			gfp_t gfp)
+	{
+		return ida_alloc_max(ida, max, gfp);
+	}"
+		add_function "
+	static inline void cas_ida_free(struct ida *ida, unsigned int id)
+	{
+		ida_free(ida, id);
+	}" ;;
+    "2")
+		add_function "
+	static inline int cas_ida_alloc_max(struct ida *ida, unsigned int max,
+			gfp_t gfp)
+	{
+		return ida_simple_get(ida, 0, max + 1, gfp);
+	}"
+		add_function "
+	static inline void cas_ida_free(struct ida *ida, unsigned int id)
+	{
+		ida_simple_remove(ida, id);
+	}" ;;
+    *)
+        exit 1
+    esac
+}
+
+conf_run $@

configure.d/1_sysfs_emit.conf

@@ -0,0 +1,34 @@
+#!/bin/bash
+#
+# Copyright(c) 2026 Unvertical
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+. $(dirname $3)/conf_framework.sh
+
+# sysfs_emit() was introduced in v5.10.
+check() {
+	cur_name=$(basename $2)
+	config_file_path=$1
+	if compile_module $cur_name "sysfs_emit(NULL, \"\");" "linux/sysfs.h"
+	then
+		echo $cur_name "1" >> $config_file_path
+	else
+		echo $cur_name "2" >> $config_file_path
+	fi
+}
+
+apply() {
+    case "$1" in
+    "1")
+		add_define "cas_sysfs_emit(buf, fmt, ...) \\
+			sysfs_emit(buf, fmt, ##__VA_ARGS__)" ;;
+    "2")
+		add_define "cas_sysfs_emit(buf, fmt, ...) \\
+			scnprintf(buf, PAGE_SIZE, fmt, ##__VA_ARGS__)" ;;
+    *)
+        exit 1
+    esac
+}
+
+conf_run $@

modules/cas_bd/exp_obj.c

@@ -117,13 +117,13 @@ static CAS_MAKE_REQ_RET_TYPE _cas_exp_obj_make_rq_fn(struct request_queue *q,
 
 static int _cas_exp_obj_allocate_minor_slot(void)
 {
-	return ida_alloc_max(&exp_obj_global.minor_ida,
+	return cas_ida_alloc_max(&exp_obj_global.minor_ida,
 			CAS_MINOR_SLOT_MAX, GFP_KERNEL);
 }
 
 static void _cas_exp_obj_free_minor_slot(int slot)
 {
-	ida_free(&exp_obj_global.minor_ida, slot);
+	cas_ida_free(&exp_obj_global.minor_ida, slot);
 }
 
 static int _cas_exp_obj_set_dev_t(struct cas_exp_obj *exp_obj,
@@ -301,7 +301,7 @@ static ssize_t device_attr_serial_show(struct device *dev,
 	struct gendisk *gd = dev_to_disk(dev);
 	struct cas_exp_obj *exp_obj = gd->private_data;
 
-	return sysfs_emit(buf, "opencas-%s", exp_obj->dev_name);
+	return cas_sysfs_emit(buf, "opencas-%s", exp_obj->dev_name);
 }
 
 static struct device_attribute device_attr_serial =