In many cases, it results in simpler code.  For example:

	-       prefix_len = str_has_prefix(name, PDSC_FW_COMPONENT_PREFIX);
	-       if (prefix_len)
	-               name += prefix_len;
	+       name = strprefix(name, PDSC_FW_COMPONENT_PREFIX) ?: name;

It avoids explicit pointer arithmetic, which also prevents certain bugs.

After this commit, only a few uses of str_has_prefix() remain.  Those
are difficult to remove, as the surrounding code is deeply based on
lengths.  Let's leave those, as it's too risky to touch that code.

Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
 drivers/net/ethernet/amd/pds_core/fw.c |  5 +--
 kernel/printk/braille.c                | 14 ++++----
 kernel/trace/trace.c                   |  9 +++---
 kernel/trace/trace_events.c            |  3 +-
 kernel/trace/trace_events_hist.c       | 44 ++++++++++++--------------
 kernel/trace/trace_events_synth.c      |  8 +++--
 kernel/trace/trace_stack.c             |  6 ++--
 7 files changed, 42 insertions(+), 47 deletions(-)

diff --git a/drivers/net/ethernet/amd/pds_core/fw.c b/drivers/net/ethernet/amd/pds_core/fw.c
index 7fe4594e9f9b..3f0b1137dd90 100644
--- a/drivers/net/ethernet/amd/pds_core/fw.c
+++ b/drivers/net/ethernet/amd/pds_core/fw.c
@@ -50,16 +50,13 @@ void pdsc_fw_components_invalidate(struct pdsc *pdsc)
 
 static u8 pdsc_name_to_fw_type(const char *name)
 {
-	size_t prefix_len;
 	int i;
 
 	/* "fw" without suffix maps to main firmware */
 	if (!strcmp(name, "fw"))
 		return PDS_CORE_FW_TYPE_MAIN;
 
-	prefix_len = str_has_prefix(name, PDSC_FW_COMPONENT_PREFIX);
-	if (prefix_len)
-		name += prefix_len;
+	name = strprefix(name, PDSC_FW_COMPONENT_PREFIX) ?: name;
 
 	for (i = 1; i < ARRAY_SIZE(pdsc_fw_type_names); i++) {
 		if (pdsc_fw_type_names[i] &&
diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 17a9591e54ff..18847d88140b 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -11,18 +11,18 @@
 
 int _braille_console_setup(char **str, char **brl_options)
 {
-	size_t len;
+	char *p;
 
-	len = str_has_prefix(*str, "brl,");
-	if (len) {
+	p = strprefix(*str, "brl,");
+	if (p) {
 		*brl_options = "";
-		*str += len;
+		*str = p;
 		return 0;
 	}
 
-	len = str_has_prefix(*str, "brl=");
-	if (len) {
-		*brl_options = *str + len;
+	p = strprefix(*str, "brl=");
+	if (p) {
+		*brl_options = p;
 		*str = strchr(*brl_options, ',');
 		if (!*str) {
 			pr_err("need port name after brl=\n");
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e8c4efa8107b..1c40a00c5bd7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4085,19 +4085,18 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 
 int trace_set_options(struct trace_array *tr, char *option)
 {
-	char *cmp;
+	char *cmp, *p;
 	int neg = 0;
 	int ret;
 	size_t orig_len = strlen(option);
-	int len;
 
 	cmp = strstrip(option);
 
-	len = str_has_prefix(cmp, "no");
-	if (len)
+	p = strprefix(cmp, "no");
+	if (p)
 		neg = 1;
 
-	cmp += len;
+	cmp = p;
 
 	mutex_lock(&event_mutex);
 	mutex_lock(&trace_types_lock);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index d467cdf9c805..72e42def1dd0 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -266,9 +266,8 @@ static struct trace_event_fields *find_event_field(const char *fmt,
 	const char *p = fmt;
 	int len;
 
-	if (!(len = str_has_prefix(fmt, "REC->")))
+	if (!(fmt = strprefix(fmt, "REC->")))
 		return NULL;
-	fmt += len;
 	for (p = fmt; *p; p++) {
 		if (!isalnum(*p) && *p != '_')
 			break;
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index c099bfbb9fb6..d5578b67ce9f 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1485,25 +1485,26 @@ static int parse_action(char *str, struct hist_trigger_attrs *attrs)
 static int parse_assignment(struct trace_array *tr,
 			    char *str, struct hist_trigger_attrs *attrs)
 {
-	int len, ret = 0;
+	char *p;
+	int ret = 0;
 
-	if ((len = str_has_prefix(str, "key=")) ||
-	    (len = str_has_prefix(str, "keys="))) {
-		attrs->keys_str = kstrdup(str + len, GFP_KERNEL);
+	if ((p = strprefix(str, "key=")) ||
+	    (p = strprefix(str, "keys="))) {
+		attrs->keys_str = kstrdup(p, GFP_KERNEL);
 		if (!attrs->keys_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if ((len = str_has_prefix(str, "val=")) ||
-		   (len = str_has_prefix(str, "vals=")) ||
-		   (len = str_has_prefix(str, "values="))) {
-		attrs->vals_str = kstrdup(str + len, GFP_KERNEL);
+	} else if ((p = strprefix(str, "val=")) ||
+		   (p = strprefix(str, "vals=")) ||
+		   (p = strprefix(str, "values="))) {
+		attrs->vals_str = kstrdup(p, GFP_KERNEL);
 		if (!attrs->vals_str) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if ((len = str_has_prefix(str, "sort="))) {
-		attrs->sort_key_str = kstrdup(str + len, GFP_KERNEL);
+	} else if ((p = strprefix(str, "sort="))) {
+		attrs->sort_key_str = kstrdup(p, GFP_KERNEL);
 		if (!attrs->sort_key_str) {
 			ret = -ENOMEM;
 			goto out;
@@ -1514,17 +1515,15 @@ static int parse_assignment(struct trace_array *tr,
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if ((len = str_has_prefix(str, "clock="))) {
-		str += len;
-
-		str = strstrip(str);
-		attrs->clock = kstrdup(str, GFP_KERNEL);
+	} else if ((p = strprefix(str, "clock="))) {
+		p = strstrip(p);
+		attrs->clock = kstrdup(p, GFP_KERNEL);
 		if (!attrs->clock) {
 			ret = -ENOMEM;
 			goto out;
 		}
-	} else if ((len = str_has_prefix(str, "size="))) {
-		int map_bits = parse_map_size(str + len);
+	} else if ((p = strprefix(str, "size="))) {
+		int map_bits = parse_map_size(p);
 
 		if (map_bits < 0) {
 			ret = map_bits;
@@ -4881,8 +4880,7 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 	struct action_data *data;
 	unsigned int i;
 	int ret = 0;
-	char *str;
-	int len;
+	char *str, *p;
 
 	for (i = 0; i < hist_data->attrs->n_actions; i++) {
 		enum handler_id hid = 0;
@@ -4890,14 +4888,14 @@ static int parse_actions(struct hist_trigger_data *hist_data)
 
 		str = hist_data->attrs->action_str[i];
 
-		if ((len = str_has_prefix(str, "onmatch(")))
+		if ((p = strprefix(str, "onmatch(")))
 			hid = HANDLER_ONMATCH;
-		else if ((len = str_has_prefix(str, "onmax(")))
+		else if ((p = strprefix(str, "onmax(")))
 			hid = HANDLER_ONMAX;
-		else if ((len = str_has_prefix(str, "onchange(")))
+		else if ((p = strprefix(str, "onchange(")))
 			hid = HANDLER_ONCHANGE;
 
-		action_str = str + len;
+		action_str = p ?: str;
 
 		switch (hid) {
 		case HANDLER_ONMATCH:
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 016ca522e5af..2a7df262aa8f 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -2268,12 +2268,14 @@ static int create_synth_event(const char *raw_command)
 
 	/* This interface accepts group name prefix */
 	if (strchr(name, '/')) {
-		len = str_has_prefix(name, SYNTH_SYSTEM "/");
-		if (len == 0) {
+		const char *n;
+
+		n = strprefix(name, SYNTH_SYSTEM "/");
+		if (!n) {
 			synth_err(SYNTH_ERR_INVALID_DYN_CMD, 0);
 			return -EINVAL;
 		}
-		name += len;
+		name = n;
 	}
 
 	len = name - raw_command;
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index e7f4e523587d..3f8ddb7b8530 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -539,10 +539,10 @@ static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
 
 static __init int enable_stacktrace(char *str)
 {
-	int len;
+	char *p;
 
-	if ((len = str_has_prefix(str, "_filter=")))
-		strscpy(stack_trace_filter_buf, str + len);
+	if ((p = strprefix(str, "_filter=")))
+		strscpy(stack_trace_filter_buf, p);
 
 	stack_tracer_enabled = 1;
 	return 1;
-- 
2.55.0