From mboxrd@z Thu Jan 1 00:00:00 1970 From: KII Keiichi Subject: Re: [PATCH v2 -mm 9/9] netconsole: Support dynamic reconfiguration using configfs Date: Fri, 13 Jul 2007 22:50:16 +0900 Message-ID: <46978318.9080804@bx.jp.nec.com> References: <20070710091920.23907.96483.sendpatchset@cselinux1.cse.iitk.ac.in> <20070710092006.23907.33652.sendpatchset@cselinux1.cse.iitk.ac.in> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Cc: Linux Kernel Mailing List , Matt Mackall , Netdev , Joel Becker , Stephen Hemminger , Andrew Morton , David Miller To: Satyam Sharma Return-path: Received: from TYO202.gate.nec.co.jp ([202.32.8.206]:57580 "EHLO tyo202.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757415AbXGMNuT (ORCPT ); Fri, 13 Jul 2007 09:50:19 -0400 In-Reply-To: <20070710092006.23907.33652.sendpatchset@cselinux1.cse.iitk.ac.in> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Hi Satyam, > From: Satyam Sharma > > [9/9] netconsole: Support dynamic reconfiguration using configfs > > This patch introduces support for dynamic reconfiguration (adding, removing > and/or modifying parameters of netconsole targets at runtime) using a > userspace interface exported via configfs. Documentation is also updated > accordingly. > > Issues and brief design overview: > > (1) Kernel-initiated creation / destruction of kernel objects is not > possible with configfs -- the lifetimes of the "config items" is managed > exclusively from userspace. But netconsole must support boot/module params > too, and these are parsed in kernel and hence netpolls must be setup from > the kernel. Joel Becker suggested to separately manage the lifetimes of > the two kinds of netconsole_target objects -- those created via configfs > mkdir(2) from userspace and those specified from the boot/module option > string. This adds complexity and some redundancy here and also means that > boot/module param-created targets are not exposed through the configfs > namespace (and hence cannot be updated / destroyed dynamically). However, > this saves us from locking / refcounting complexities that would need to > be introduced in configfs to support kernel-initiated item creation / > destroy there. Also, this is similar to present behaviour in any case so > not really a problem. > > (2) In configfs, item creation takes place in the call chain of the mkdir(2) > syscall in the driver subsystem. If we used an ioctl(2) to create / destroy > objects from userspace, the special userspace program is able to fill out > the structure to be passed into the ioctl and hence specify attributes such > as local interface that are required at the time we set up the netpoll. > For configfs, this information is not available at the time of mkdir(2). > So, we keep all newly-created targets (via configfs) disabled by default. > The user is expected to set various attributes appropriately (including the > local network interface if required) and then write(2) "1" to the "enabled" > attribute. Thus, netpoll_setup() is then called on the set parameters in the > context of _this_ write(2) on the "enabled" attribute itself. This design > enables the user to reconfigure existing netconsole targets at runtime to > be attached to newly-come-up interfaces that may not have existed when > netconsole was loaded or when the targets were actually created. This all > enables us to get rid of custom ioctls. > > (3) Ultra-paranoid configfs attribute show() and store() operations, with > sanity and input range checking, using only safe string primitives, and > compliant with the recommendations in Documentation/filesystems/sysfs.txt. > > (4) A new function netpoll_print_options() is created in the netpoll API, > that just prints out the configured parameters for a netpoll structure. > netpoll_parse_options() is modified to use that and it is also exported to > be used from netconsole. > > Signed-off-by: Satyam Sharma > Cc: Keiichi Kii > Acked-by: Keiichi Kii Thanks -- Keiichi KII NEC Corporation OSS Platform Development Division E-mail: k-keiichi@bx.jp.nec.com