From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Becker Subject: Re: [RFC 02/22] configfs: Add struct configfs_item_operations->check_link() in configfs_unlink() Date: Fri, 10 Sep 2010 12:44:04 -0700 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Konrad Rzeszutek Wilk , linux-scsi , linux-kernel , FUJITA Tomonori , Mike Christie , Christoph Hellwig , Hannes Reinecke , James Bottomley , Jens Axboe , Boaz Harrosh , Linux-fsdevel To: "Nicholas A. Bellinger" Return-path: Content-Disposition: inline In-Reply-To: <1284145606.19890.68.camel@haakon2.linux-iscsi.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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(). > 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. > 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. Joel -- "I have never let my schooling interfere with my education." - Mark Twain Joel Becker Consulting Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127