From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gao Xiang Subject: Re: [PATCH v5] fs: introduce is_dot_or_dotdot helper for cleanup Date: Wed, 11 Dec 2019 15:17:11 +0800 Message-ID: <20191211071711.GA231266@architecture4> References: <1576030801-8609-1-git-send-email-yangtiezhu@loongson.cn> <20191211024858.GB732@sol.localdomain> <20191211044723.GC4203@ZenIV.linux.org.uk> <4a90aaa9-18c8-f0a7-19e4-1c5bd5915a28@loongson.cn> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Content-Disposition: inline In-Reply-To: <4a90aaa9-18c8-f0a7-19e4-1c5bd5915a28@loongson.cn> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Transfer-Encoding: 7bit To: Tiezhu Yang Cc: Al Viro , Eric Biggers , Matthew Wilcox , "Theodore Y. Ts'o" , Jaegeuk Kim , Chao Yu , Tyler Hicks , 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" 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 >