Add struct ksw_config and ksw_parse_config() to parse user string.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 mm/kstackwatch/kernel.c      | 112 +++++++++++++++++++++++++++++++++++
 mm/kstackwatch/kstackwatch.h |  27 +++++++++
 2 files changed, 139 insertions(+)

diff --git a/mm/kstackwatch/kernel.c b/mm/kstackwatch/kernel.c
index 78f1d019225f..3b7009033dd4 100644
--- a/mm/kstackwatch/kernel.c
+++ b/mm/kstackwatch/kernel.c
@@ -1,16 +1,128 @@
 // SPDX-License-Identifier: GPL-2.0
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/kstrtox.h>
 #include <linux/module.h>
+#include <linux/string.h>
+
+#include "kstackwatch.h"
+
+static struct ksw_config *ksw_config;
+
+struct param_map {
+	const char *name;       /* long name */
+	const char *short_name; /* short name (2 letters) */
+	size_t offset;          /* offsetof(struct ksw_config, field) */
+	bool is_string;         /* true for string */
+};
+
+/* macro generates both long and short name automatically */
+#define PMAP(field, short, is_str) \
+	{ #field, #short, offsetof(struct ksw_config, field), is_str }
+
+static const struct param_map ksw_params[] = {
+	PMAP(func_name,   fn, true),
+	PMAP(func_offset, fo, false),
+	PMAP(depth,       dp, false),
+	PMAP(max_watch,   mw, false),
+	PMAP(sp_offset,   so, false),
+	PMAP(watch_len,   wl, false),
+};
+
+static int ksw_parse_param(struct ksw_config *config, const char *key,
+			   const char *val)
+{
+	const struct param_map *pm = NULL;
+	int ret;
+
+	for (int i = 0; i < ARRAY_SIZE(ksw_params); i++) {
+		if (strcmp(key, ksw_params[i].name) == 0 ||
+		    strcmp(key, ksw_params[i].short_name) == 0) {
+			pm = &ksw_params[i];
+			break;
+		}
+	}
+
+	if (!pm)
+		return -EINVAL;
+
+	if (pm->is_string) {
+		char **dst = (char **)((char *)config + pm->offset);
+		*dst = kstrdup(val, GFP_KERNEL);
+		if (!*dst)
+			return -ENOMEM;
+	} else {
+		ret = kstrtou16(val, 0, (u16 *)((char *)config + pm->offset));
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+/*
+ * Configuration string format:
+ *    param_name=<value> [param_name=<value> ...]
+ *
+ * Required parameters:
+ * - func_name  |fn (str) : target function name
+ * - func_offset|fo (u16) : instruction pointer offset
+ *
+ * Optional parameters:
+ * - depth      |dp (u16) : recursion depth
+ * - max_watch  |mw (u16) : maximum number of watchpoints
+ * - sp_offset  |so (u16) : offset from stack pointer at func_offset
+ * - watch_len  |wl (u16) : watch length (1,2,4,8)
+ */
+static int __maybe_unused ksw_parse_config(char *buf, struct ksw_config *config)
+{
+	char *part, *key, *val;
+	int ret;
+
+	kfree(config->func_name);
+	kfree(config->user_input);
+	memset(ksw_config, 0, sizeof(*ksw_config));
+
+	buf = strim(buf);
+	config->user_input = kstrdup(buf, GFP_KERNEL);
+	if (!config->user_input)
+		return -ENOMEM;
+
+	while ((part = strsep(&buf, " \t\n")) != NULL) {
+		if (*part == '\0')
+			continue;
+
+		key = strsep(&part, "=");
+		val = part;
+		if (!key || !val)
+			continue;
+		ret = ksw_parse_param(config, key, val);
+		if (ret)
+			pr_warn("unsupported param %s=%s", key, val);
+	}
+
+	if (!config->func_name || !config->func_offset) {
+		pr_err("Missing required parameters: function or func_offset\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
 
 static int __init kstackwatch_init(void)
 {
+	ksw_config = kzalloc(sizeof(*ksw_config), GFP_KERNEL);
+	if (!ksw_config)
+		return -ENOMEM;
+
 	pr_info("module loaded\n");
 	return 0;
 }
 
 static void __exit kstackwatch_exit(void)
 {
+	kfree(ksw_config);
+
 	pr_info("module unloaded\n");
 }
 
diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index 0273ef478a26..a7bad207f863 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -2,4 +2,31 @@
 #ifndef _KSTACKWATCH_H
 #define _KSTACKWATCH_H
 
+#include <linux/types.h>
+
+#define MAX_CONFIG_STR_LEN 128
+
+struct ksw_config {
+	char *func_name;
+	u16 depth;
+
+	/*
+	 * watched variable info:
+	 * - func_offset : instruction offset in the function, typically the
+	 *                 assignment of the watched variable, where ksw
+	 *                 registers a kprobe post-handler.
+	 * - sp_offset   : offset from stack pointer at func_offset. Usually 0.
+	 * - watch_len   : size of the watched variable (1, 2, 4, or 8 bytes).
+	 */
+	u16 func_offset;
+	u16 sp_offset;
+	u16 watch_len;
+
+	/* max number of hwbps that can be used */
+	u16 max_watch;
+
+	/* save to show */
+	char *user_input;
+};
+
 #endif /* _KSTACKWATCH_H */
-- 
2.43.0