linux-kernel - Re: [PATCH v5] fs: introduce is_dot_or

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Message-ID: <20191211044723.GC4203@ZenIV.linux.org.uk>
Date:   Wed, 11 Dec 2019 04:47:23 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>,
        Tyler Hicks <tyhicks@...onical.com>,
        linux-fsdevel@...r.kernel.org, ecryptfs@...r.kernel.org,
        linux-fscrypt@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup

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.