On Wed, Dec 11, 2019 at 02:38:34PM +0800, Tiezhu Yang wrote:
> 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] == '.')) {
And I suggest drop "unlikely" here since files start with prefix
'.' (plus specical ".", "..") are not as uncommon as you expected...
Thanks,
Gao Xiang
> 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
>
