linux-kernel - Re: [PATCH 1/2] SCSI: Add a SCSI option for persistent device names in Kernel.

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Date:	Fri, 8 Apr 2011 09:12:12 -0700
From:	Greg KH <greg@...ah.com>
To:	Nao Nishijima <nao.nishijima.xt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-hotplug@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Jon Masters <jcm@...hat.com>, 2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH 1/2] SCSI: Add a SCSI option for persistent device names
 in Kernel.

On Fri, Apr 08, 2011 at 11:07:41PM +0900, Nao Nishijima wrote:
> Hi,
> 
> (2011/04/06 1:14), Greg KH wrote:
> > On Tue, Apr 05, 2011 at 09:49:46PM +0900, Nao Nishijima wrote:
> >> This patch series provides a SCSI option for persistent device
> >> names in kernel. With this option, user can always assign a
> >> same device name (e.g. sda) to a specific device according to
> >> udev rules and device id.
> >>
> >> Issue:
> >> Recently, kernel registers block devices in parallel. As a result,
> >> different device names will be assigned at each boot time. This
> >> will confuse file-system mounter, thus we usually use persistent
> >> symbolic links provided by udev. However, dmesg and procfs outputs
> >> show device names instead of the symbolic link names. This causes
> >> a serious problem when managing multiple devices (e.g. on a
> >> large-scale storage), because usually, device errors are output
> >> with device names on dmesg. We also concern about some commands
> >> which output device names, as well as kernel messages.
> >>
> >> Solution:
> >> To assign a persistent device name, I create unnamed devices (not
> >> a block device, but an intermediate device. users cannot read/write
> >> this device). When scsi device driver finds a LU, the LU is registered
> >> as an unnamed device and inform to udev. After udev finds the unnamed
> >> device, udev assigns a persistent device name to a specific device
> >> according to udev rules and registers it as a block device. Hence,
> >> this is just a naming, not a renaming.
> >>
> >> Some users are satisfied with current udev solution. Therefore, my
> >> proposal is implemented as an option.
> >>
> >> If using this option, add the following kernel parameter.
> >>
> >> 	scsi_mod.persistent_name=1
> >>
> >> Also, if you want to assign a device name with sda, add the
> >> following udev rules.
> >>
> >> SUBSYSTEM=="scsi_unnamed", ATTR{disk_id}=="xxx", PROGRAM="/bin/sh
> >> -c 'echo -n sda > /sys/%p/disk_name'"
> > 
> > Also, where is the "real" program you have created to properly name
> > devices from userspace?  You need that to properly test this patch,
> > right?
> > 
> 
> In the udev rule described above, notation “xxx” indicated by
> ATTR(disk_id) is scsi id given by disk. Then, when udev finds this rule,
> "/bin/sh -c 'echo -n sda>  /sys/%p/disk_name'" indicated by PROGRAM is
> operated using xxx (scsi id) if udev find the disk with scic id xxx.
> Thus, persistent device name is assigned.
> 
> I have tested this patch using the udev rule. and It works well.

That's nice, but it's a "toy".  What have you used to test this with
20000 scsi devices to properly work like it does today?  Where is the
program that will name them in a deterministic manner?

We have that functionality today, you can't break it.

thanks,

greg k-h
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