Re: [PATCH 08/12] printk: Replace strncmp with str_has_prefix

[Joe Perches]

On Thu, 2019-08-01 at 23:23 +0800, Chuhong Yuan wrote:
> Joe Perches <j...@perches.com> 于2019年7月30日周二 上午8:16写道：
> > On Mon, 2019-07-29 at 23:15 +0800, Chuhong Yuan wrote:
> > > strncmp(str, const, len) is error-prone.
> > > We had better use newly introduced
> > > str_has_prefix() instead of it.
> > []
> > > diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
> > []
> > > @@ -11,10 +11,10 @@
> > > 
> > >  int _braille_console_setup(char **str, char **brl_options)
> > >  {
> > > -     if (!strncmp(*str, "brl,", 4)) {
> > > +     if (str_has_prefix(*str, "brl,")) {
> > >               *brl_options = "";
> > >               *str += 4;
> > > -     } else if (!strncmp(*str, "brl=", 4)) {
> > > +     } else if (str_has_prefix(*str, "brl=")) {
> > >               *brl_options = *str + 4;
> > 
> > Better to get rid of the += 4 uses too by storing the result
> > of str_has_prefix and using that as the addend.
> > 
> > Perhaps
> >         size_t len;
> > 
> >         if ((len = str_has_prefix(*str, "brl,"))) {
> >                 *brl_options = "";
> >                 *str += len;
> >         } else if ((len = str_has_prefix(*str, "brl="))) {
> >                 etc...
> > 
> 
> I find that checkpatch.pl forbids assignment in if condition.
> So this seems to be infeasible...

So the code could be rewritten like below:
(though it's trivial as-is)
---
 kernel/printk/braille.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c
index 1d21ebacfdb8..46dd9fcc7525 100644
--- a/kernel/printk/braille.c
+++ b/kernel/printk/braille.c
@@ -11,19 +11,29 @@
 
 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 = strchr(*brl_options, ',');
-               if (!*str) {
-                       pr_err("need port name after brl=\n");
-                       return -EINVAL;
-               }
-               *((*str)++) = 0;
+               *str += len;
+               return 0;
+       }
+
+       len = str_has_prefix(*str, "brl=");
+       if (!len)
+               return 0;
+
+       *brl_options = *str + len;
+
+       *str = strchr(*brl_options, ',');
+       if (!*str) {
+               pr_err("need port name after brl=\n");
+               return -EINVAL;
        }
 
+       *((*str)++) = 0;
+
        return 0;
 }