Re: [PATCH 1/2] SCSI: Add a SCSI option for persistent device names

[Nao Nishijima <nao.nishijima.xt@hitachi.com>]

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.


> thanks,
> 
> greg k-h
> 

Thanks,

-- 
Nao NISHIJIMA
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., YOKOHAMA Research  Laboratory
Email： nao.nishijima.xt@hitachi.com