[PATCH v4 4/8] printk: Replace strncmp with str_has_prefix

[Chuhong Yuan]

strncmp(str, const, len) is error-prone because len
is easy to have typo.
The example is the hard-coded len has counting error
or sizeof(const) forgets - 1.
So we prefer using newly introduced str_has_prefix()
to substitute such strncmp to make code better.

Signed-off-by: Chuhong Yuan <hsleste...@gmail.com>
---
Changes in v4:
  - Eliminate assignments in if conditions.

 kernel/printk/braille.c | 15 +++++++++++----
 kernel/printk/printk.c  | 22 ++++++++++++++++------
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 1d21ebacfdb8..17a9591e54ff 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -11,11 +11,18 @@
 
 int _braille_console_setup(char **str, char **brl_options)
 {
-       if (!strncmp(*str, "brl,", 4)) {
+       size_t len;
+
+       len = str_has_prefix(*str, "brl,");
+       if (len) {
                *brl_options = "";
-               *str += 4;
-       } else if (!strncmp(*str, "brl=", 4)) {
-               *brl_options = *str + 4;
+               *str += len;
+               return 0;
+       }
+
+       len = str_has_prefix(*str, "brl=");
+       if (len) {
+               *brl_options = *str + len;
                *str = strchr(*brl_options, ',');
                if (!*str) {
                        pr_err("need port name after brl=\n");
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1888f6a3b694..43a31015ec93 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -118,19 +118,29 @@ static unsigned int __read_mostly devkmsg_log = 
DEVKMSG_LOG_MASK_DEFAULT;
 
 static int __control_devkmsg(char *str)
 {
+       size_t len;
+
        if (!str)
                return -EINVAL;
 
-       if (!strncmp(str, "on", 2)) {
+       len = str_has_prefix(str, "on");
+       if (len) {
                devkmsg_log = DEVKMSG_LOG_MASK_ON;
-               return 2;
-       } else if (!strncmp(str, "off", 3)) {
+               return len;
+       }
+
+       len = str_has_prefix(str, "off");
+       if (len) {
                devkmsg_log = DEVKMSG_LOG_MASK_OFF;
-               return 3;
-       } else if (!strncmp(str, "ratelimit", 9)) {
+               return len;
+       }
+
+       len = str_has_prefix(str, "ratelimit");
+       if (len) {
                devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
-               return 9;
+               return len;
        }
+
        return -EINVAL;
 }
 
-- 
2.20.1