Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup

[Tiezhu Yang]

On 12/11/2019 12:47 PM, Al Viro wrote:
> On Wed, Dec 11, 2019 at 11:59:40AM +0800, Tiezhu Yang wrote:
>
> > static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
> > {
> >          if (len == 1 && name[0] == '.')
> >                  return true;
> >
> >          if (len == 2 && name[0] == '.' && name[1] == '.')
> >                  return true;
> >
> >          return false;
> > }
> >
> > Hi Matthew,
> >
> > How do you think? I think the performance influence is very small
> > due to is_dot_or_dotdot() is a such short static inline function.
> It's a very short inline function called on a very hot codepath.
> Often.
>
> I mean it - it's done literally for every pathname component of
> every pathname passed to a syscall.

OK. I understand. Let us do not use the helper function in fs/namei.c,
just use the following implementation for other callers:

static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
{
        if (len >= 1 && unlikely(name[0] == '.')) {
                if (len < 2 || (len == 2 && name[1] == '.'))
                        return true;
        }

        return false;
}

Special thanks for Matthew, Darrick, Al and Eric.
If you have any more suggestion, please let me know.

Thanks,

Tiezhu Yang