From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [RFC] Disk shock protection (revisited) Date: Tue, 26 Feb 2008 12:39:46 +0000 Message-ID: <20080226123946.75dbe3d2@core> References: <87skzgd1zk.fsf@denkblock.local> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:35344 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751473AbYBZMu2 (ORCPT ); Tue, 26 Feb 2008 07:50:28 -0500 In-Reply-To: <87skzgd1zk.fsf@denkblock.local> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Elias Oltmanns Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe > The general idea: A daemon running in user space monitors input data > from an accelerometer. When the daemon detects a critical condition, That sounds like a non starter. What if the box is busy, what if the daemon or something you touch needs memory and causes paging ? Given the accelerometer data should be very simple doesn't it actually make sense in this specific case to put the logic (not thresholds) in kernel space. > state. To this end, the kernel has to issue an idle immediate command > with unload feature and stop the block layer queue afterwards. Once the Yep. Pity the worst case completion time for an IDE I/O is 60 seconds or so. > 1. Who is to be in charge for the shock protection application? Should > userspace speak to libata / ide directly (through sysfs) and the low I think it has to be kernel side for speed, and because you will need to issue idle immediate while a command sequence is active which is *extremely* hairy as you have to recover from the mess and restart the relevant I/O. Plus you may need controller specific knowledge on issuing it (and changes to libata). > 2. Depending on the answer to the previous question, by what mechanism > should block layer and lld interact? Special requests, queue hooks or > something in some way similar to power management functions (once > suggested by James Bottomley)? Idle immediate seem to simply fit the queue model, it happens in *parallel* to I/O events and is special in all sorts of ways. > 3. What is the preferred way to pass device specific configuration > options to libata (preferrably at runtime, i.e., after module > loading)? sysfs