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

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Message-ID: <4a90aaa9-18c8-f0a7-19e4-1c5bd5915a28@loongson.cn>
Date:   Wed, 11 Dec 2019 14:38:34 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Al Viro <viro@...iv.linux.org.uk>
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,
        "Darrick J. Wong" <darrick.wong@...cle.com>
Subject: Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup

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