2019-08-05 12:25:34

by Chuhong Yuan

Subject: [PATCH v3 4/8] printk: Replace strncmp with str_has_prefix

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 <[email protected]>
---
Changes in v3:
- Revise the description.
- Remove else uses in printk.c.

kernel/printk/braille.c | 10 ++++++----
kernel/printk/printk.c | 19 +++++++++++++------
2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 1d21ebacfdb8..e451b8b1d3d5 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -11,11 +11,13 @@

int _braille_console_setup(char **str, char **brl_options)
{
- if (!strncmp(*str, "brl,", 4)) {
+ size_t len;
+
+ if ((len = str_has_prefix(*str, "brl,"))) {
*brl_options = "";
- *str += 4;
- } else if (!strncmp(*str, "brl=", 4)) {
- *brl_options = *str + 4;
+ *str += len;
+ } else if ((len = str_has_prefix(*str, "brl="))) {
+ *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..6b8d9cfebc0b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -118,19 +118,26 @@ 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)) {
+ if ((len = str_has_prefix(str, "on"))) {
devkmsg_log = DEVKMSG_LOG_MASK_ON;
- return 2;
- } else if (!strncmp(str, "off", 3)) {
+ return len;
+ }
+
+ if ((len = str_has_prefix(str, "off"))) {
devkmsg_log = DEVKMSG_LOG_MASK_OFF;
- return 3;
- } else if (!strncmp(str, "ratelimit", 9)) {
+ return len;
+ }
+
+ if ((len = str_has_prefix(str, "ratelimit"))) {
devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
- return 9;
+ return len;
}
+
return -EINVAL;
}

--
2.20.1

2019-08-06 08:09:00

by Geert Uytterhoeven

Subject: Re: [PATCH v3 4/8] printk: Replace strncmp with str_has_prefix

Hi Chuhong,

On Mon, Aug 5, 2019 at 2:24 PM Chuhong Yuan <[email protected]> wrote:
> 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 <[email protected]>

Thanks for your patch!

> --- a/kernel/printk/braille.c
> +++ b/kernel/printk/braille.c
> @@ -11,11 +11,13 @@
>
> int _braille_console_setup(char **str, char **brl_options)
> {
> - if (!strncmp(*str, "brl,", 4)) {
> + size_t len;
> +
> + if ((len = str_has_prefix(*str, "brl,"))) {

Please write this as

len = str_has_prefix(*str, "brl,");
if (len) {

(everywhere)

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds