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Date:   Wed, 11 Dec 2019 04:47:23 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Eric Biggers <ebiggers@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup
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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.