Computer Help for the New and Veteran User for Linux

UDEV Primer Misc Devices

Palm Pilots, USB and udev

By: Chris Atkinson

This section describes how to set up a Palm Pilot USB cradle to synch on a pure udev system.

I'll assume that you have properly configured your system to work with your Palm Pilot.

The Palm Pilot only exists in sysfs after HotSynch button is pressed and prior to completion, cancellation or expiration of the synch. This means that you will be pressing the synch button a lot of times before you're sorted.

First, plug the cradle into your USB port. Press the hotsynch button on the cradle. Then run dmesg.

The result should be similar to:

usb 2-1: new full speed USB device using address 2

Now we need to burrow into sysfs to find this new full speed USB device. Try in /sys/class/tty. While the hotsynch is active, change to the /sys/class/tty directory and run a listing, as follows.

bash-2.05b# cd /sys/class/tty
bash-2.05b# ls
console  tty12  tty19  tty25  tty31  tty38  tty44  tty50  tty57  tty63  ttyS3
ptmx     tty13  tty2   tty26  tty32  tty39  tty45  tty51  tty58  tty7   ttyS4
tty      tty14  tty20  tty27  tty33  tty4   tty46  tty52  tty59  tty8   ttyS5
tty0     tty15  tty21  tty28  tty34  tty40  tty47  tty53  tty6   tty9   ttyS6
tty1     tty16  tty22  tty29  tty35  tty41  tty48  tty54  tty60  ttyS0  ttyS7
tty10    tty17  tty23  tty3   tty36  tty42  tty49  tty55  tty61  ttyS1  ttyUSB0
tty11    tty18  tty24  tty30  tty37  tty43  tty5   tty56  tty62  ttyS2  ttyUSB1

The entry we're interested in is the last one, ttyUSB1. (Both USB links are created by the Palm Pilot, but only the latter does anything, so we'll disregard ttyUSB0.)

Let's double check, though. Wait until the hotsynch has timed out and then rerun the list command. The two ttyUSB entries should have vanished.

Now that we know which entry in sysfs we care about, let's use udevinfo to track down the data we'll need for our udev rules, as follows:

bash-2.05b$ udevinfo -p /sys/class/tty/ttyUSB1 -a

One of the entries is of interest:

looking at the device chain at '/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1'                 :
    SYSFS{bMaxPower}="  2mA"
    SYSFS{bNumInterfaces}=" 1"
    SYSFS{manufacturer}="Palm, Inc."
    SYSFS{product}="Palm Handheld"
    SYSFS{version}=" 1.00"

With this information we can create a udev rule in the /etc/udev/rules.d/10-udev.rules file which will create an entry in /dev for the Palm Pilot. There are a variety of ways to do this, the one I is use is as follows:

#Chris Palm Pilot

BUS="usb", SYSFS{serial}="123456789ABC", NAME="pilot"

Now we need to set the permissions for the new pilot device. Since it is better practice to leave the default settings in the /etc/udev/permissions.d/50-udev.permissions file alone, we need to create a /etc/udev/permissions.d/10-udev.permissions file containing the following entry to make the device world read/write:

#set Palm Pilot rw

Now let's check to see if it worked. First, press the hotsynch button. Now issue a nice, harmless command to the Palm to list its files:

bash-2.05b$ pilot-xfer -p /dev/pilot -L

You should get a nice list of your Palm Pilot's files. Now, just make sure that whatever GUI interface you use with your Palm is looking at the /dev/pilot device (rather than, say, TTYUSB), and you're ready to go.

USB Thumb/Flash Drives

By: Chris Atkinson

One common device type about which questions are frequently asked is the USB drive/thumbdrive/keychain drive. This is a finger-sized device which can be inserted into a USB port and mounted as a harddrive.

This just covers the udev. aspects of using such a drive. I'd recommend reviewing a more general tutorial on these drives, to make sure that you've covered the non-udev issues as well.

One non-udev issue to note is that, starting in some of the 2.6.9 kernels, an option to compile in support for usb block drives rather than using SCSI emulation. Since this is pretty new, I'll give examples using both the old sd* devices and the new ub* devices.

To start, let's insert the drive and run a dmesg. Using SCSI emulation, the last line of the output should look like

usb 1-2: new high speed USB device using address 2
Initializing USB Mass Storage driver...
scsi0 : SCSI emulation for USB Mass Storage devices
Vendor: 128MB Model: USB2.0FlashDrive Rev:
Type: Direct-Access ANSI SCSI revision: 02
USB Mass Storage device found at 2
usbcore: registered new driver usb-storage
USB Mass Storage support registered.
SCSI device sda: 251904 512-byte hdwr sectors (129 MB)
sda: Write Protect is off
sda: Mode Sense: 03 00 00 00
sda: assuming drive cache: write through
sda: sda4
Attached scsi removable disk sda at scsi0, channel 0, id 0, lun 0

Or, if you are using the 2.6.9+ usb block device support, like:

usb 1-2: new high speed USB device using address 2
ub: sizeof ub_scsi_cmd 60 ub_dev 924
uba: device 2 capacity nsec 256000 bsize 512
uba: was not changed
uba: uba1
usbcore: registered new driver ub

We now hunt for this device in /sys. The tricky piece is that you are not looking for the device sda (or uba) but rather for its partition sda4 (or uba1). So we run the command

udevinfo -p /sys/block/sda/sda4 -a

Or, for the new ub* devices:

udevinfo -p /sys/block/uba/uba1 -a

The interesting part of the output might look similar too:

looking at the device chain at '/sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1':
SYSFS{bMaxPower}=" 84mA"
SYSFS{bNumInterfaces}=" 1"
SYSFS{manufacturer}="Power by USB"
SYSFS{product}="USB 2.0 Flash Drive "
SYSFS{version}=" 2.00"

We then create a rule in /etc/udev/rules.d/10-udev.rules as follows:

#Black USB Thumb Drive

BUS="usb", SYSFS{serial}="A083014282978", NAME="blackthumb"

We check to make sure that the thumbdrive is now present as a device in /dev with the we assigned it:

ls -la /dev | grep thumb

If it is there, we now add an entry to the /etc/fstab file to allow it to be mounted.

The following shows the entry for a single-partitioned vfat-formatted drive set up to be mountable by any user. Change as you see fit for your situation.

/dev/thumb /mnt/thumbdrive vfat noauto,user,umask=000 0 0

Now, lets mount it and make sure it's where we expect it to be.

mount /dev/thumb
cd /mnt/thumbdrive


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