From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 24 Oct 2002 19:36:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 24 Oct 2002 19:36:12 -0400 Received: from host194.steeleye.com ([66.206.164.34]:27666 "EHLO pogo.mtv1.steeleye.com") by vger.kernel.org with ESMTP id ; Thu, 24 Oct 2002 19:36:11 -0400 Message-Id: <200210242342.g9ONgGT04819@localhost.localdomain> X-Mailer: exmh version 2.4 06/23/2000 with nmh-1.0.4 To: Steven Dake cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] [RFC] Advanced TCA SCSI Disk Hotswap In-Reply-To: Message from Steven Dake of "Thu, 24 Oct 2002 13:45:48 PDT." <3DB85BFC.2080009@mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Thu, 24 Oct 2002 18:42:16 -0500 From: James Bottomley X-AntiVirus: scanned for viruses by AMaViS 0.2.1 (http://amavis.org/) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > The locking most definately needs to be added to the kernel. I'm > surprised the original patch didn't contain any locking, but then > again, my first patch didn't either:) When I first read the SCSI code many years ago, I found surprise wasn't adequate and I was forced to resort to astonishment. It's being cleaned up slowly. Originally hot removal/insertion was the exception, so nobody tripped over the locking issue. Now it's fast becoming the rule. > This may be true, but most systems will only have at most 4-5 devices. > > Theres only so much room on PCI for FC devices :) I have to think about other SCSI systems as well. Some IBM beasties have > 256 PCI slots. Infiniband is threatening direct bus-fibre attachment. > In Advanced TCA (what spawned this work) a button is pressed to > indicate hotswap removal which makes for easy detection of hotswap > events. This is why there are kernel interfaces for removal and > insertion (so a kernel driver can be written to detect the button > press and remove the devices from the os data structures and then > light a blue led indicating safe for removal). OK, I understand what's going on now. It's no different from those hotplug PCI busses where you press the button and a second or so later the LED goes out and you can remove the card. 10ms sounds rather a short maximum time for a technician to wait for a light to go out....I suppose Telco technicians are rather impatient. I really think you need to lengthen this interval. The kernel is moving towards this type of hotplug infrastructure which you can easily leverage (or even help build), but it's definitely going to be mainly in user space. James