From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiang Liu Subject: Re: [PATCH] fs: namespace: Simplify function commit_tree() Date: Tue, 13 Jan 2015 13:33:24 +0800 Message-ID: <54B4AE24.6030906@linux.intel.com> References: <1421125686-23765-1-git-send-email-jiang.liu@linux.intel.com> <20150113052801.GH22149@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Al Viro Return-path: In-Reply-To: <20150113052801.GH22149@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 2015/1/13 13:28, Al Viro wrote: > On Tue, Jan 13, 2015 at 01:08:06PM +0800, Jiang Liu wrote: >> Simplify function commit_tree() in fs/namespace.c, it also improves code >> readability. > > Huh? > >> static void commit_tree(struct mount *mnt, struct mount *shadows) >> { >> struct mount *parent = mnt->mnt_parent; >> - struct mount *m; >> - LIST_HEAD(head); >> struct mnt_namespace *n = parent->mnt_ns; >> >> BUG_ON(parent == mnt); >> - >> - list_add_tail(&head, &mnt->mnt_list); >> - list_for_each_entry(m, &head, mnt_list) >> - m->mnt_ns = n; >> - >> - list_splice(&head, n->list.prev); >> - >> + mnt->mnt_ns = n; >> + list_add_tail(&mnt->mnt_list, &n->list); > > And who will set ->mnt_ns on other mounts reachable via ->mnt_list from mnt? > Not to mention putting them on n->list... > > What you seem to have missed is that list_add_tail(&head, &mnt->mnt_list) > is not the same thing as list_add_tail(&mnt->mnt_list, &head). We are > not ripping mnt->mnt_list from whatever list it was on and insert it into > a previously empty one in head. We take an unanchored cyclic list (all > elements being some_mnt->mnt_list) and anchor it at head, then go through > all elements of the original list and move them all at once into the > end of n->list. Hi Al, Sorry for the noise, didn't realized that mnt->mnt_list anchors a whole list:( Regards! Gerry