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Tino Keitel | 24 Sep 21:58

Differend udev names with different kernels

Hi,

what's the intention of /dev/disk/by-id/?

My firewire hard disk seems to have different names with different
kernels.

With 2.6.26.3, it's name is
/dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.

With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
the disk has the same name.

With 2.6.27-rc7, it is called
/dev/disk/by-id/scsi-1WDC_WD10EACS-00D6B0_WD-WCAU41668315.

One major config difference is that 2.6.26.3 has CONFIG_FIREWIRE and
CONFIG_FIREWIRE_SBP2 set to "m", whereas the 2.6.27 kernels have set
them to "y". But that doesn't explain the difference between both
2.6.27-rc kernels.

Shouldn't these names be somewhat constant? Otherwise they would be
totally useless.

Regards,
Tino
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Kay Sievers | 25 Sep 05:12
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Re: Differend udev names with different kernels

On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
> what's the intention of /dev/disk/by-id/?
>
> My firewire hard disk seems to have different names with different
> kernels.
>
> With 2.6.26.3, it's name is
> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>
> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
> the disk has the same name.
>
> With 2.6.27-rc7, it is called
> /dev/disk/by-id/scsi-1WDC_WD10EACS-00D6B0_WD-WCAU41668315.

Seems, for some reason, the "ieee1394_id" attribute becomes readable
because of lucky timing, which wasn't the case before.

> One major config difference is that 2.6.26.3 has CONFIG_FIREWIRE and
> CONFIG_FIREWIRE_SBP2 set to "m", whereas the 2.6.27 kernels have set
> them to "y". But that doesn't explain the difference between both
> 2.6.27-rc kernels.

I guess, it's just a not-easy-to-reproduce timing issue with the sysfs
attribute.

> Shouldn't these names be somewhat constant? Otherwise they would be
> totally useless.

Yeah, sure they should not change like this.
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Stefan Richter | 25 Sep 07:08

Re: Differend udev names with different kernels

Kay Sievers wrote:
> On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
>> what's the intention of /dev/disk/by-id/?
>>
>> My firewire hard disk seems to have different names with different
>> kernels.
>>
>> With 2.6.26.3, it's name is
>> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>>
>> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
>> the disk has the same name.

Then this is a regression of the fastboot patch or whatever.

I will watch what will happen in 2.6.28-rc.

>> With 2.6.27-rc7, it is called
>> /dev/disk/by-id/scsi-1WDC_WD10EACS-00D6B0_WD-WCAU41668315.
> 
> Seems, for some reason, the "ieee1394_id" attribute becomes readable
> because of lucky timing, which wasn't the case before.
> 
>> One major config difference is that 2.6.26.3 has CONFIG_FIREWIRE and
>> CONFIG_FIREWIRE_SBP2 set to "m", whereas the 2.6.27 kernels have set
>> them to "y". But that doesn't explain the difference between both
>> 2.6.27-rc kernels.
> 
> I guess, it's just a not-easy-to-reproduce timing issue with the sysfs
> attribute.
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Tino Keitel | 25 Sep 07:47

Re: Differend udev names with different kernels

On Thu, Sep 25, 2008 at 07:08:20 +0200, Stefan Richter wrote:
> Kay Sievers wrote:
>> On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
>>> what's the intention of /dev/disk/by-id/?
>>>
>>> My firewire hard disk seems to have different names with different
>>> kernels.
>>>
>>> With 2.6.26.3, it's name is
>>> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>>>
>>> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
>>> the disk has the same name.
>
> Then this is a regression of the fastboot patch or whatever.

It has the same name with 2.6.26.3 and with 2.6.27-rc7-something with
fastboot merged. So why would this be a regression? The different name
(scsi-...) happended with a vanilla 2.6.27-rc7.

Initially, my intention was to find a unique name for the hard disk,
that stays even if the disk is changed from Firewire to USB. However,
this doesn't seem to be possible with a default udev.

Regards,
Tino
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Stefan Richter | 25 Sep 23:13

Re: Differend udev names with different kernels

Tino Keitel wrote:

Tino, when you reply on LKML, please keep _all_ responders in a thread 
in the Cc list.  I for one am not subscribed to linux-hotplug, and I may 
easily miss a response on LKML with its hundreds of messages per day if 
I am not Cc'd.  Thanks.

> On Thu, Sep 25, 2008 at 07:08:20 +0200, Stefan Richter wrote:
>> Kay Sievers wrote:
>>> On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
>>>> what's the intention of /dev/disk/by-id/?
>>>>
>>>> My firewire hard disk seems to have different names with different
>>>> kernels.
>>>>
>>>> With 2.6.26.3, it's name is
>>>> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>>>>
>>>> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
>>>> the disk has the same name.
>> Then this is a regression of the fastboot patch or whatever.
> 
> It has the same name with 2.6.26.3 and with 2.6.27-rc7-something with
> fastboot merged. So why would this be a regression? The different name
> (scsi-...) happended with a vanilla 2.6.27-rc7.

I misunderstood.  (Comprehension difficulties at 0700 AM.)

It is of course intended that FireWire disks get the 
/dev/disk/by-id/ieee1394-* link.  Only this one is reliably unique.  The
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Tino Keitel | 25 Sep 23:23

Re: Differend udev names with different kernels

On Thu, Sep 25, 2008 at 23:13:19 +0200, Stefan Richter wrote:

[...]

>> Initially, my intention was to find a unique name for the hard disk,
>> that stays even if the disk is changed from Firewire to USB. However,
>> this doesn't seem to be possible with a default udev.

[...]

> An alternative though would be filesystem labels or filesystem UUIDs, if  
> unique and persistent identifiers at the filesystem level rather than at  
> the block device level are sufficient for your needs.

Not really. My initial problem was that a volume sometimes came up very
late, so that the lvm2 initscript didn't activate that volume group. So
I wanted to wait for this specific disk during boot. Meanwhile, I
created an udev rule that uses the vendor and device name, which also
has the advantage of being the same when the disk is connected via
Firewire and USB (or, should be the same at least, I didn't test USB
yet).

Regards,
Tino
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Stefan Richter | 25 Sep 07:59

Re: Differend udev names with different kernels

I wrote:
>> On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
>>> My firewire hard disk seems to have different names with different
>>> kernels.
>>>
>>> With 2.6.26.3, it's name is
>>> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>>>
>>> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
>>> the disk has the same name.
> 
> Then this is a regression of the fastboot patch or whatever.
> 
> I will watch what will happen in 2.6.28-rc.
> 
>>> With 2.6.27-rc7, it is called
>>> /dev/disk/by-id/scsi-1WDC_WD10EACS-00D6B0_WD-WCAU41668315.

Uh, sorry, I misunderstood.  It is a regression of mainline then.

> The scsi-* link may not be unique because it may be based on unsuitable
> information generated by the SBP-2 bridge device's firmware.
...
> I will look into it.
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Kay Sievers | 25 Sep 08:09
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Re: Differend udev names with different kernels

On Wed, Sep 24, 2008 at 22:59, Stefan Richter <stefanr <at> s5r6.in-berlin.de> wrote:
> I wrote:
>>>
>>> On Wed, Sep 24, 2008 at 13:01, Tino Keitel <tino.keitel <at> gmx.de> wrote:
>>>>
>>>> My firewire hard disk seems to have different names with different
>>>> kernels.
>>>>
>>>> With 2.6.26.3, it's name is
>>>> /dev/disk/by-id/ieee1394-0030e001e0006585:00043c:0000.
>>>>
>>>> With someting after 2.6.27-rc7, merged with Arjan's fastboot branch,
>>>> the disk has the same name.
>>
>> Then this is a regression of the fastboot patch or whatever.
>>
>> I will watch what will happen in 2.6.28-rc.
>>
>>>> With 2.6.27-rc7, it is called
>>>> /dev/disk/by-id/scsi-1WDC_WD10EACS-00D6B0_WD-WCAU41668315.
>
> Uh, sorry, I misunderstood.  It is a regression of mainline then.

Yeah, I have more reports from people, that with recent kernels, the
ieee1394-* links showed up and replaced the scsi-* links, which they
say never happended before.
We ship these rules for a long time now, so I just guessed, they never
really worked before, but as all depends on timing, it's probably not
predictable what happens. Regardless of the needed fix for scsi sysfs,
we should provide both links, I guess.
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