From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754649Ab0IJT4K (ORCPT ); Fri, 10 Sep 2010 15:56:10 -0400 Received: from smtp126.sbc.mail.sp1.yahoo.com ([69.147.65.185]:41462 "HELO smtp126.sbc.mail.sp1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753036Ab0IJT4I (ORCPT ); Fri, 10 Sep 2010 15:56:08 -0400 X-Yahoo-SMTP: fzDSGlOswBCWnIOrNw7KwwK1j9PqyNbe5PtLKiS4dDU.UNl_t6bdEZu9tTLW X-YMail-OSG: JkLCNa0VM1nAZgOVxnTMhSp4IQMlmzwfilmuFVvIv0ddyVq WZlGRfVo5VufYT0KksnDyiOLIj7iVbtzDjy5UwGixmTLtaA4HlMvjMqjAZl. 2oSdLAmddPCdTQzQTv_H8s_RtrY5jq8KC_KaDDOiXUcNGahPkNrnNZbcr7wK .AiDVyztI1cs8sGwyfhm9TL9IsBZPturvY8mrbMqUPxRj0wP3ZyEKDy0lB1w sXOAK.jjNOZGAOO.URjDUryC0MZ_AyO7Z6I0tF06Wb5ikLx0BfdAeBS4w1dX sYwcnszeh5sBx5b3.5svJtj0- X-Yahoo-Newman-Property: ymail-3 Subject: Re: [RFC 02/22] configfs: Add struct configfs_item_operations->check_link() in configfs_unlink() From: "Nicholas A. Bellinger" To: Joel Becker Cc: Konrad Rzeszutek Wilk , linux-scsi , linux-kernel , FUJITA Tomonori , Mike Christie , Christoph Hellwig , Hannes Reinecke , James Bottomley , Jens Axboe , Boaz Harrosh , Linux-fsdevel In-Reply-To: <20100910194404.GJ885@mail.oracle.com> References: <1283160025-6598-1-git-send-email-nab@linux-iscsi.org> <20100902064814.GB27904@mail.oracle.com> <1283456440.5598.108.camel@haakon2.linux-iscsi.org> <201009071701.02847.konrad@darnok.org> <20100907224413.GC21935@mail.oracle.com> <1283911739.556.420.camel@haakon2.linux-iscsi.org> <20100908192639.GD29545@mail.oracle.com> <1283979207.556.510.camel@haakon2.linux-iscsi.org> <20100910152802.GG885@mail.oracle.com> <1284145606.19890.68.camel@haakon2.linux-iscsi.org> <20100910194404.GJ885@mail.oracle.com> Content-Type: text/plain Date: Fri, 10 Sep 2010 12:52:03 -0700 Message-Id: <1284148323.19890.94.camel@haakon2.linux-iscsi.org> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-09-10 at 12:44 -0700, Joel Becker wrote: > On Fri, Sep 10, 2010 at 12:06:46PM -0700, Nicholas A. Bellinger wrote: > > On Fri, 2010-09-10 at 08:28 -0700, Joel Becker wrote: > > > The trivial solution is to refcount your ACLs. You get both > > > allow_link() calls, so you should be able to increment a counter there, > > > and then drop them when the last drop_link() call is made. That will > > > keep your consumer structures around until all links are exhausted. > > > > > > > So I am a bit confused wrt to this last response.. The ->check_link() > > patch and it's use in the fabric independent code within > > target_core_fabric_configfs.c does exactly this for the 'MappedLUN' > > symlink case, eg: requires the consumer to do the allow_link() + > > drop_link() refcounting, and add the > > API check into fs/configfs/symlink.c:configfs_unlink() > > You can refcount without check_link(). So what do you recommend here..? > > > Is there another form of configfs consumer refcounting that you had in > > mind beyond using an atomic_t for this with ->check_link() here..? > > I'm saying that you won't crash if you don't free the ACLs on > the first drop_link(). That is, the drop_link() goes through as > configfs wants it to, but you don't crash. The problem is that the 'unlink sub_child/group1/src_0/src_link' can't signal to the other struct config_group to also call an internal 'unlink sub_child/group2/dst_0/dst_link' to drop the child link outside of it's struct config_group. > > > So beyond a configfs consumer solution, what do you think about checking > > for the sub_child/group2/dst_0/dst_link style of symlink > > in fs/configfs/symlink.c:configfs_symlink() in order to add some form of > > internal refcount when the symlink source is within the same consumer > > LKM, but outside of the parent struct config_group..? > > > > This would involve the conversion of fs/configfs/symlink.c: > > configfs_unlink() path to check for the existence of this internal > > refcount and returning -EPERM when any sub_child/group2/dst_0/dst_link > > exist when 'unlink sub_child/group1/src_0/src_link' is attempted. > > You're still fighting allowing the links to go away. You > haven't explained why that is necessary. You had a problem with a crash > because you expected one reference to your ACLs and actually have two, > but you can fix that without modifying configfs. If this is the case then I must be mis-understanding what you mean by configfs consumer refcounting from allow_link() and drop_link(). Can you give me a bit more detail where I should be looking..? Thanks! --nab