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Subject: Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup
To:     Al Viro <viro@zeniv.linux.org.uk>
References: <1576030801-8609-1-git-send-email-yangtiezhu@loongson.cn>
 <20191211024858.GB732@sol.localdomain>
 <febbd7eb-5e53-6e7c-582d-5b224e441e37@loongson.cn>
 <20191211044723.GC4203@ZenIV.linux.org.uk>
Cc:     Eric Biggers <ebiggers@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        Tyler Hicks <tyhicks@canonical.com>,
        linux-fsdevel@vger.kernel.org, ecryptfs@vger.kernel.org,
        linux-fscrypt@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org,
        "Darrick J. Wong" <darrick.wong@oracle.com>
From:   Tiezhu Yang <yangtiezhu@loongson.cn>
Message-ID: <4a90aaa9-18c8-f0a7-19e4-1c5bd5915a28@loongson.cn>
Date:   Wed, 11 Dec 2019 14:38:34 +0800
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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