Working on a usb-storage hotplug script

[Martin <drink@hyperlogos.org>]

I recently got my first USB flash drive - I have one on loan from work, 
but I finally OWN one, so I am motivated to do something with it now. 
One of the things I want to have working is hotplugging, with automatic 
mounting. The device it's mounted on doesn't matter so much but one of 
the absolutely mandatory requirements is that I not need a fstab entry. 
This became a requirement when I noticed that plugging the device in, 
then unplugging it, then plugging it BACK in resulted in it being 
attached first to sdc and then to sdd. (This is a SCSI system.)

Before I go on, some relevant information:
Linux suckit 2.4.20-xfs-r3 #3 SMP Fri Nov 28 14:20:48 PST 2003 i686 AMD 
Athlon(tm) Processor AuthenticAMD GNU/Linux
(This is the gentoo xfs-sources version of the kernel.)
Hotplug version 20030805-r2
usbcore, usb-ohci, and usb-storage modules all load as they should.

So I began to google for a usb-storage hotplug script which would do 
what I want. Alas, no such thing exists. The closest script I found 
really didn't work to begin with, so I set out to write something. 
Unfortunately there seems to be no simple way to get from the 
information that hotplug will feed one about the connected mass storage 
device to the particular scsi device which it has been attached to.

I began by writing a script which probably looks familiar to everyone 
who's worked on this problem.

#!/bin/bash
echo "ACTION ${ACTION}" >> /tmp/usblog
echo "PRODUCT ${PRODUCT}" >> /tmp/usblog
echo "TYPE ${TYPE}" >> /tmp/usblog
echo "INTERFACE ${INTERFACE}" >> /tmp/usblog
echo "DEVFS ${DEVFS}" >> /tmp/usblog
echo "DEVICE ${DEVICE}" >> /tmp/usblog

This resulted in the following output upon insertion of my flash drive:

ACTION add
PRODUCT ea0/6828/110
TYPE usb
INTERFACE 8/6/80
DEVFS /proc/bus/usb
DEVICE /proc/bus/usb/001/006

By looking in the usb and scsi nodes under /proc I decided that the only 
unique information between the two trees was the serial number.

/proc/bus/usb/devices (as you know)  is an ascii file which contains 
long descriptions of every connected usb device in the system.

Each device begins with a T: line, here is the entry for my flash drive.

T:  Bus\x01 Lev\x01 Prnt\x01 Port\x01 Cnt\x01 Dev#=  6 Spd\x12  MxCh= 0
D:  Ver= 1.10 Cls\0(>ifc ) Sub\0 Prot\0 MxPSd #Cfgs=  1
P:  Vendor\x0ea0 ProdIDh28 Rev= 1.10
S:  Manufacturer=USB    
S:  Product=Flash Disk     
S:  SerialNumber#0760A43F777AB2
C:* #Ifs= 1 Cfg#= 1 AtrÄ MxPwr\x100mA
I:  If#= 0 Alt= 0 #EPs= 3 Cls\b(stor.) Sub\x06 ProtP Driver=usb-storage
E:  AdÅ(I) Atr\x02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad\x02(O) Atr\x02(Bulk) MxPS=  64 Ivl=0ms
E:  AdÉ(I) Atr\x03(Int.) MxPS=   2 Ivl%5ms

our device is 001/006 which is bus/dev. so we can use the T: line to 
find our device. This is useful because there is only one T: line per 
device. After this I went to find the serial number (S:  SerialNumber=*)

Then I went to look in /proc/scsi/usb-storage-* to find devices. 
/proc/scsi/usb-storage-0/1 looks like so:

   Host scsi1: usb-storage
       Vendor: USB    
      Product: Flash Disk     
Serial Number: 230760A43F777AB2
     Protocol: Transparent SCSI
    Transport: Bulk
         GUID: 0ea06828230760a43f777ab2
     Attached: Yes

So we can see that our serial number matches. The first line of the file 
tells me the Host which I will obviously need. Looking in /proc/scsi/scsi:

Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: IBM      Model: DDRS-39130D      Rev: DC1B
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
  Vendor: SEAGATE  Model: ST39140N         Rev: 1498
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 06 Lun: 00
  Vendor: IBM      Model: CDRM00203     !K Rev: BZ26
  Type:   CD-ROM                           ANSI SCSI revision: 02
Host: scsi1 Channel: 00 Id: 00 Lun: 00
  Vendor: 64MB     Model: HardDrive        Rev: 1.88
  Type:   Direct-Access                    ANSI SCSI revision: 02

unfortunately the entries here are not really unique in any way if you 
have more than one of the same thing. The Revision from the 
/proc/bus/usb/devices might be used to HELP identify something, but it 
still will not be unique. The question is, what happens when I plug in 
another one? Will it get a new host? Answer is yes. The device also 
shows up in a new usb-storage-? directory under /proc/scsi. Here is its 
entry in usb/devices:

T:  Bus\x01 Lev\x01 Prnt\x01 Port\x01 Cnt\x02 Dev#=  6 Spd\x12  MxCh= 0
D:  Ver= 1.10 Cls\0(>ifc ) Sub\0 Prot\0 MxPSd #Cfgs=  1
P:  Vendor\x0ea0 ProdIDh28 Rev= 1.10
S:  Manufacturer=USB    
S:  Product=Flash Disk     
S:  SerialNumber#0760A43F777AB2
C:* #Ifs= 1 Cfg#= 1 AtrÄ MxPwr\x100mA
I:  If#= 0 Alt= 0 #EPs= 3 Cls\b(stor.) Sub\x06 ProtP Driver=usb-storage
E:  AdÅ(I) Atr\x02(Bulk) MxPS=  64 Ivl=0ms
E:  Ad\x02(O) Atr\x02(Bulk) MxPS=  64 Ivl=0ms
E:  AdÉ(I) Atr\x03(Int.) MxPS=   2 Ivl%5ms

And here is the new entry in /proc/scsi/scsi:

Host: scsi2 Channel: 00 Id: 00 Lun: 00
  Vendor: JetFlash Model: 128MB            Rev: 1.11
  Type:   Direct-Access                    ANSI SCSI revision: 02

Obviously I don't have two identical flash devices to play with, or I 
would be using them.

Does the Port\x01 correspond to the usb-storage-? directory in 
/proc/scsi? That is the only number which seems to have gone from 0 to 
1. I only have two flash devices so I can't tell for sure by installing 
another one. The new device has an entry in usb-storage-1/2 rather than 
1/1 as I would have suspected. The Cnt\x02 leads me to believe that Port 
becomes the usb-storage-? directory and Cnt becomes the filename under 
that directory. Are my assumptions correct? If so I can do away with 
most of my nonsense about the serial number, it was just the first thing 
I came up with.

I do have one further problem before I even start, which is that I don't 
seem to get a remove event when I disconnect a flash drive. Is this a 
known problem with my version of the kernel or of hotplug?



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