From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nao Nishijima Subject: Re: [PATCH 1/2] SCSI: Add a SCSI option for persistent device names in Kernel. Date: Tue, 12 Apr 2011 22:23:55 +0900 Message-ID: <4DA4526B.2030609@hitachi.com> References: <20110405124946.7969.66796.stgit@ltc233.sdl.hitachi.co.jp> <20110405161400.GA885@kroah.com> <4D9F17DF.5030601@hitachi.com> <4D9F1CD1.2020600@suse.de> <1302275652.4090.10.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1302275652.4090.10.camel@mulgrave.site> Sender: linux-hotplug-owner@vger.kernel.org To: James Bottomley Cc: Hannes Reinecke , Greg KH , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-hotplug@vger.kernel.org, Kay Sievers , Jon Masters , 2nddept-manager@sdl.hitachi.co.jp List-Id: linux-scsi@vger.kernel.org Hi, James (2011/04/09 0:14), James Bottomley wrote: > On Fri, 2011-04-08 at 07:33 -0700, Hannes Reinecke wrote: >>> The problem I would like to discuss here is that users can not iden= tify >>> a disk from kernel messages when they DIRECTLY refer to these messa= ges. >>> For example, a device name is used instead of a symbolic link names= in >>> bootup messages, I/O devices errors and /proc/partitions =E2=80=A6e= tc. >>> >>> In particular, users can not identify an appropriate device from a >>> device name in syslog since different device name may be assigned t= o it >>> at each boot time. >>> >>> My idea is able to fix this issue with small changes in scsi subsys= tem. >>> Also, it is implemented as an option. Therefore, it does not affect >>> users who do not select this option. >>> >> We have been discussing this problem several times in the past, and >> indeed on these very mailing list. >> >> The conclusion we arrived at is that the kernel-provided device node >> name is inherently unstable and impossible to fix within the existin= g >> 'sdX' naming scheme. >> So the choices have been to either move to a totally different namin= g >> scheme or keep the naming scheme and provide the required informatio= n >> by other means. >> We have decided on the latter, and agreed on using udev to provide >> persistent device names. >> We are fully aware that any kernel related messages are subject to >> chance after reboot, but then most kernel related messages are >> (PID number, timestamps, login tty etc). >> And also we are aware that any kernel messages need to be matched >> against the current system layout to figure out any hardware-related >> issue. >> >> But then basically all products requiring to filter out information >> from kernel messages already do so I don't see a problem with that. >> >> Just adding an in-kernel identifier to the LUN will only be an >> incomplete solution, as other identifiers will still be volatile. >> >> So I would prefer by keeping the in-kernel information as small >> as possible to reduce memory consumption and rely on out-of-band >> programs to provide the required mapping. >=20 > So, while I agree totally with the above: udev and userspace is the w= ay > to go, I'm not totally opposed to having a non-invasive mechanism for > indicating a user's preferred name for a device. I think there are a > couple of ways to do this: >=20 > 1. Entirely in userspace: just have udev consult a preferred nam= e > file and create say /dev/disk/by-preferred. Then have all th= e > tools that normally output device information do the same (i.= e. > since real name to preferred name is 1:1, they could all do a > reverse lookup). > 2. have a writeable sysfs preferred_name field, either in the > generic device or just in SCSI. The preferred name would be > used by outbound only (i.e. kernel dev_printk messages and > possibly /proc/partitions). All inbound uses of the device > would come via the standard udev mechanisms > (i.e. /dev/disk/by-preferred would be the usual symlink). Th= is > means from the kernel point of view, no renaming has happened= =2E > We'd just try to print out the preferred name in certain > circumstances, which should solve most of the described probl= em. >=20 > James >=20 >=20 >=20 I have a question. Why is in-kernel device name necessary? The kernel can identify a device by major/miner number and udev can create a device node of a prefer name. Currently, device names are only used to show to users. Therefore I think that in-kernel device name is unnecessary if we introduce your /dev/disk/by-prefferd idea. thanks, --=20 Nao NISHIJIMA Software Platform Research Dept. Linux Technology Center Hitachi, Ltd., YOKOHAMA Research Laboratory Email=EF=BC=9A nao.nishijima.xt@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-hotplug= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html