Re: [PATCH 1/2] SCSI: Add a SCSI option for persistent device namesin Kernel.

From: Greg KH
Date: Fri Apr 08 2011 - 12:13:25 EST

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 âxxxâ 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.


greg k-h
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