Identical USB devices rules

Identical USB devices rules

[James Finnall]

Hello All,

New to the list and searched the archives some but unable to locate something 
on identical hotplug devices for writing rules.  I am running udev and I had 
a custom rule for an external drive enclosure as follows:

SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk/drv%n"

This works as desired for either of my devices that are identical when only 
one is attached.  But today I had a need to clone one drive to another using 
both devices at the same time.  I found that udev assigned the device 
assignments to the 2nd drive unit as the first drive.

The kernel originally used /dev/sde and /dev/sdf for each of the drives when 
they were connected.  And of course these could change depending on what else 
may be connected at any given time by USB or IEEE1394.  Being unable to 
identify them separately in a rule to be sequential, I could only remark out 
the rule above and then proceed with the kernel names that were assigned.

Is there a way to sequentially assign the drives using the name convention 
above as in /dev/disk1/drv%n and /dev/disk2/drv%n when using multiple devices 
that are identical?

Thank you for your consideration.
James



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Re: Identical USB devices rules

[Kay Sievers]

On Wed, 2006-08-02 at 18:09 -0400, James Finnall wrote:
> New to the list and searched the archives some but unable to locate something 
> on identical hotplug devices for writing rules.  I am running udev and I had 
> a custom rule for an external drive enclosure as follows:
> 
> SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk/drv%n"
> 
> This works as desired for either of my devices that are identical when only 
> one is attached.  But today I had a need to clone one drive to another using 
> both devices at the same time.  I found that udev assigned the device 
> assignments to the 2nd drive unit as the first drive.
> 
> The kernel originally used /dev/sde and /dev/sdf for each of the drives when 
> they were connected.  And of course these could change depending on what else 
> may be connected at any given time by USB or IEEE1394.  Being unable to 
> identify them separately in a rule to be sequential, I could only remark out 
> the rule above and then proceed with the kernel names that were assigned.
> 
> Is there a way to sequentially assign the drives using the name convention 
> above as in /dev/disk1/drv%n and /dev/disk2/drv%n when using multiple devices 
> that are identical?

Almost all recent distros ship the persistent disk links maintained by
udev which create /dev/disk/by-{id,label,uuid,path} directories and put
symlinks in there. If you clone disks you copy uuid and label, which
breaks by-label and by-uuid, but by-path should still work. If your
drive enclosure is not one of the real cheap ones, you get a serial
number there, which should make by-id work.

Kay


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Re: Identical USB devices rules

[James Finnall]

Thank you for the response.   From the udevinfo returned from the units they 
are identical, even the serial number.   Of course, the hard disk is most apt 
to change every time I use the device so that info is not of any value to me.   

The only thing I found I could use here was to write two rules and then select 
them by the USB ID field, ID="3-2" and ID="3-4".   At present that seems to 
work OK on my system.   I only have three USB ports and one is used for a USB 
mouse.  So I have to use the other two for operations like this.  So I think 
these rules should be OK.  So my rules lare ike below now.

ID="3-2",SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk/drv%n"
ID="3-4",SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk1/drv%n"

Not really a good way to identify, because I think it so system specific on 
the hardware support.   To allow identical devices to be distinguished 
differently only by the actual port it is connected removes the true hot plug 
and play operation.  Ideally, it shouldn't matter which port it is connected 
or at least it should be invisible to the user creating the rules.  On my 
system each port is both USB level 1 and USB level 2.   These are different 
controllers and are on different busses.   The "3" in ID="3-2" indicates it 
is on buss 3 from what I am able to determine.   My mouse is only USB level 1 
and it is on USB buss "2".   The rules have to then be created for every 
device multiple times if they are identical.   For my instance, ideally, the 
first drive connected to any port should get the first assignment.  Then the 
2nd drive connected gets the next assignment but within the single rule.   
But with the rules above the drive that is connected to that specific port 
will get the assigned devices, regardless of whether it is first or not.   
Now, that may not always be undesirable either.   Like my circumstances 
cloning a hard disk, I think I actually prefer the method above.   That way I 
know which drive is the source drive of the operation.

Thank you once again for your consideration.
James

On Thursday 03 August 2006 03:38, Kay Sievers wrote:
> On Wed, 2006-08-02 at 18:09 -0400, James Finnall wrote:
> > New to the list and searched the archives some but unable to locate
> > something on identical hotplug devices for writing rules.  I am running
> > udev and I had a custom rule for an external drive enclosure as follows:
> >
> > SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk/drv%n"
> >
> > This works as desired for either of my devices that are identical when
> > only one is attached.  But today I had a need to clone one drive to
> > another using both devices at the same time.  I found that udev assigned
> > the device assignments to the 2nd drive unit as the first drive.
> >
> > The kernel originally used /dev/sde and /dev/sdf for each of the drives
> > when they were connected.  And of course these could change depending on
> > what else may be connected at any given time by USB or IEEE1394.  Being
> > unable to identify them separately in a rule to be sequential, I could
> > only remark out the rule above and then proceed with the kernel names
> > that were assigned.
> >
> > Is there a way to sequentially assign the drives using the name
> > convention above as in /dev/disk1/drv%n and /dev/disk2/drv%n when using
> > multiple devices that are identical?
>
> Almost all recent distros ship the persistent disk links maintained by
> udev which create /dev/disk/by-{id,label,uuid,path} directories and put
> symlinks in there. If you clone disks you copy uuid and label, which
> breaks by-label and by-uuid, but by-path should still work. If your
> drive enclosure is not one of the real cheap ones, you get a serial
> number there, which should make by-id work.
>
> Kay
>
>
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Re: Identical USB devices rules

[Kay Sievers]

On Thu, 2006-08-03 at 08:56 -0400, James Finnall wrote:
> Thank you for the response.   From the udevinfo returned from the units they 
> are identical, even the serial number.   Of course, the hard disk is most apt 
> to change every time I use the device so that info is not of any value to me.   
> 
> The only thing I found I could use here was to write two rules and then select 
> them by the USB ID field, ID="3-2" and ID="3-4".   At present that seems to 
> work OK on my system.   I only have three USB ports and one is used for a USB 
> mouse.  So I have to use the other two for operations like this.  So I think 
> these rules should be OK.  So my rules lare ike below now.
> 
> ID="3-2",SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk/drv%n"
> ID="3-4",SYSFS{idVendor}="0402", SYSFS{idProduct}="5642", NAME="disk1/drv%n"
> 
> Not really a good way to identify, because I think it so system specific on 
> the hardware support.

Please look at the the persistent disk rules. I'm not talking about USB
vendor/product numbers. Serious USB-ata bridges export the disks serial
number like the disk on its native interface would do.

>    To allow identical devices to be distinguished 
> differently only by the actual port it is connected removes the true hot plug 
> and play operation.  Ideally, it shouldn't matter which port it is connected 
> or at least it should be invisible to the user creating the rules.  On my 
> system each port is both USB level 1 and USB level 2.   These are different 
> controllers and are on different busses.   The "3" in ID="3-2" indicates it 
> is on buss 3 from what I am able to determine.   My mouse is only USB level 1 
> and it is on USB buss "2".   The rules have to then be created for every 
> device multiple times if they are identical.   For my instance, ideally, the 
> first drive connected to any port should get the first assignment.  Then the 
> 2nd drive connected gets the next assignment but within the single rule.

Nope, we are not going to implement another form of dumb and
unpredictable enumeration. :)
   
> But with the rules above the drive that is connected to that specific port 
> will get the assigned devices, regardless of whether it is first or not.   
> Now, that may not always be undesirable either.   Like my circumstances 
> cloning a hard disk, I think I actually prefer the method above.   That way I 
> know which drive is the source drive of the operation.

Again, take a look at the persistent rules for disks and input devices
and start from there.

Kay


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