Mapping /dev/*st0* to fixed names using scsi_id

Mapping /dev/*st0* to fixed names using scsi_id

[John Stoffel]

Hi all,

I've been pounding my head against this issue for a while, and cursing
the lack of comments in the example rules for udev.  Basically, I've
got a tape library with two drives and a robot on a Debian system,
with a bunch of SCSI devices including disks and tapes.  The robot is
easy, I just use the following snippet:

    # SCSI ATL P1000 Autoloader - make if /dev/changer
    BUS="scsi", SYSFS{model}="P1000     6220051",SYSFS{vendor}="ATL",SYMLINK="changer"

And it works fine.  Now I want to map the two tape drives to some
fixed names:

    /dev/nst?a  -> /dev/dlt7k-{left,right}

easily.  I used to do this with the script I posted way back in 2008
to list this, found at:

    http://article.gmane.org/gmane.linux.hotplug.devel/12579

But I never followed up on it.  Lately, it's been taking multiple
invocations of 'udevadm trigger' after each reboot to make my tape
devices show up properly.  So now I'm trying to figure out what I can
do.

Right now, I've got a rule which looks like this, which works, but
maps to /dev/sg# instead of the proper /dev/nst#a device:

    SUBSYSTEM="scsi_generic", PROGRAM="/lib/udev/scsi_id --replace-whitespace --whitelisted /dev/%k",RESULT="SQUANTUM_DLT7000_CX752S1059", SYMLINK="dlt7k-left"

I've looked at the /lib/udev/rules.d/60-persistent-storage-tape.rules
but I honestly can't make heads or tails of the ${DEV_BSG} stuff,
since it's not documented to explan what's really going on here.

I think I need to add the --whitelisted arg to the scsi_id command to
make this section work properly:

    KERNEL="st*[0-9]|nst*[0-9]",           ENV{ID_SERIAL}!="?*", \
	    SUBSYSTEMS="scsi", KERNELS="[0-9]*:*[0-9]", \
	    ENV{BSG_DEV}="$root/bsg/$id"
    KERNEL="st*[0-9]|nst*[0-9]",           ENV{ID_SERIAL}!="?*", \
	    WAIT_FOR="$env{BSG_DEV}", \
	    ENV{ID_BUS}="scsi", \
	    IMPORT{program}="scsi_id --export --device=$env{BSG_DEV}"

    KERNEL="st*[0-9]|nst*[0-9]",           ENV{ID_SERIAL}="?*", \
	    SYMLINK+="tape/by-id/$env{ID_BUS}-$env{ID_SERIAL}"

    KERNEL="st*[0-9]|nst*[0-9]", \
	    IMPORT{program}="path_id $devpath"
    KERNEL="st*[0-9]",                     ENV{ID_PATH}="?*", \
	    SYMLINK+="tape/by-path/$env{ID_PATH}"
    KERNEL="nst*[0-9]",                    ENV{ID_PATH}="?*", \
	    SYMLINK+="tape/by-path/$env{ID_PATH}-nst"

But the path_id script called here is poorly documented and hard to
follow.  Sorry for sounding whiny, but it's a pain to figure out
without well documented examples.

Can anyone point me in the right direction here?  

Thanks,
John

Re: Mapping /dev/*st0* to fixed names using scsi_id

[John Stoffel]

>>>>> "John" = John Stoffel <john@stoffel.org> writes:

John> I've been pounding my head against this issue for a while, and
John> cursing the lack of comments in the example rules for udev.

I'm still cursing, but I've been reading the docs over and over again
and I've come up with some ideas.

Basically, I need to map my tape device to a scsi_generic device, so
I can then run '/lib/udev/scsi_id --whitelisted --export --device=%k'
on the generic device, to get back a useable $ID_SERIAL that I can use
to match.

I hit upon the idea of using the following as a basic match:

    # Find SCSI_TAPE devices, export SCSI_ID env in "#:#:#:#" format 
    SUBSYSYEMS="scsi",ATTRS{type}="1",ENV{SCSI_ID}="%k"

    # Wait for SCSI_ID, then get the /dev/sg# for this tape
    SUBSYSYEMS="scsi",ATTRS{type}="1",WAIT_FOR="$env{SCSI_ID}", \
      IMPORT{program}="/lib/udev/sg_dev $env{SCSI_ID}"  

    # Wait for SG_DEV, then get the /dev/sg# for this tape
    SUBSYSYEMS="scsi",ATTRS{type}="1",WAIT_FOR="$env{SG_DEV}", \
      IMPORT{program}="/lib/udev/scsi_id --replace-whitespace
      --whitelisted --export --device=$env{SG_DEV}"  

    # Wait for ID_SERIAL and then name the tape device
    SUBSYSYEMS="scsi",ATTRS{type}="1",WAIT_FOR="$env{ID_SERIAL}", \
      ENV{ID_SERIAL}="SQUANTUM_DLT7000_CX752S1059", SYMLINK="dlt7k-left"


And the /lib/udev/sg_dev script is just the trivially simple, but hard
to do (to me at least) in udev script:

    #!/bin/sh

    lsscsi -g $1 | awk '{print "SG_DEV=" $NF}'


BUT!  This doesn't quite address all the issues, since I really need
to have some way to create symlinks to a bunch of /dev/st#[alm ]
devices, and I'm not sure how to do this.  

Any hints?  


I've also tried looking at the output of 

  udevadm info -a -p /sys/class/scsi_tape/st0 > /tmp/st0
  udevadm info -a -p /sys/class/scsi_tape/st0a > /tmp/st0a

and diffing it, but I only see the following, which doesn't help me.
Is there a way to view the minor number(s) of a device from within
UDEV easily?

    # diff -u /tmp/st0* |less
    --- /tmp/st0    2009-06-04 16:58:44.000000000 -0400
    +++ /tmp/st0a   2009-06-04 16:58:14.000000000 -0400
    @@ -5,11 +5,11 @@
     A rule to match, can be composed by the attributes of the device
     and the attributes from one single parent device.

    -  looking at device '/class/scsi_tape/st0':
    -    KERNEL="st0"
    +  looking at device '/class/scsi_tape/st0a':
    +    KERNEL="st0a"
	 SUBSYSTEM="scsi_tape"
	 DRIVER=""
    -    ATTR{defined}="1"
    +    ATTR{defined}="0"
	 ATTR{default_blksize}="-1"
	 ATTR{default_density}="-1"
	 ATTR{default_compression}="-1"


So I would suspect that Udev knows about the major/minor device
numbers, but the docs on

  http://reactivated.net/writing_udev_rules.html 

don't talk about them at all to any useful degree.

Can anyone tell me if I'm on the right track here?

Thanks,
John

Re: Mapping /dev/*st0* to fixed names using scsi_id

[John Huttley]

Hi,
I had similar issues with my collection of scsi tape drives, not all of 
which may be powered up.
 the --page=0x80 does the trick.

my kernel is compiled with the SG version4 block device option enabled.


this is my 60-persistent-storage-tape.rules, hope it helps


ACTION!="add|change", GOTO="persistent_storage_tape_end"

# type 8 devices are "Medium Changers"
KERNEL="sg[0-9]*", SUBSYSTEMS="scsi", ATTRS{type}="8", 
IMPORT{program}="scsi_id --sg-version=3 --page=0x80 --export 
--whitelisted -d $tempnode", 
SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}"

SUBSYSTEM!="scsi_tape", GOTO="persistent_storage_tape_end"

KERNEL="st*[0-9]|nst*[0-9]", ATTRS{ieee1394_id}="?*", 
ENV{ID_SERIAL}="$attr{ieee1394_id}", ENV{ID_BUS}="ieee1394"
KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", SUBSYSTEMS="usb", 
IMPORT{program}="usb_id --export %p"

KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", SUBSYSTEMS="scsi", 
KERNELS="[0-9]*:*[0-9]", ENV{BSG_DEV}="$root/bsg/$id"
KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", 
WAIT_FOR="$env{BSG_DEV}", IMPORT="scsi_id --page=0x80 --whitelisted 
--export --device=$env{BSG_DEV}", ENV{ID_BUS}="scsi"

KERNEL="st*[0-9]",  ENV{ID_SERIAL}="?*", 
SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}"
KERNEL="nst*[0-9]", ENV{ID_SERIAL}="?*", 
SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}-nst"

# by-path (shortest physical path)
KERNEL="st*[0-9]", IMPORT{program}="path_id %p"
KERNEL="st*[0-9]", ENV{ID_PATH}="?*", 
SYMLINK+="tape/by-path/$env{ID_PATH}"

LABEL="persistent_storage_tape_end"

Re: Mapping /dev/*st0* to fixed names using scsi_id

[John Stoffel]

John> I had similar issues with my collection of scsi tape drives, not
John> all of which may be powered up.  the --page=0x80 does the trick.

Interesting.  I'll try this out today if I get a chance.  

John> my kernel is compiled with the SG version4 block device option enabled.

I think mine is too. 

John> this is my 60-persistent-storage-tape.rules, hope it helps


John> ACTION!="add|change", GOTO="persistent_storage_tape_end"

John> # type 8 devices are "Medium Changers"
John> KERNEL="sg[0-9]*", SUBSYSTEMS="scsi", ATTRS{type}="8", 
John> IMPORT{program}="scsi_id --sg-version=3 --page=0x80 --export 
John> --whitelisted -d $tempnode", 
John> SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}"

John> SUBSYSTEM!="scsi_tape", GOTO="persistent_storage_tape_end"

John> KERNEL="st*[0-9]|nst*[0-9]", ATTRS{ieee1394_id}="?*", 
John> ENV{ID_SERIAL}="$attr{ieee1394_id}", ENV{ID_BUS}="ieee1394"
John> KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", SUBSYSTEMS="usb", 
John> IMPORT{program}="usb_id --export %p"

John> KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", SUBSYSTEMS="scsi", 
John> KERNELS="[0-9]*:*[0-9]", ENV{BSG_DEV}="$root/bsg/$id"
John> KERNEL="st*[0-9]|nst*[0-9]", ENV{ID_SERIAL}!="?*", 
John> WAIT_FOR="$env{BSG_DEV}", IMPORT="scsi_id --page=0x80 --whitelisted 
John> --export --device=$env{BSG_DEV}", ENV{ID_BUS}="scsi"

John> KERNEL="st*[0-9]",  ENV{ID_SERIAL}="?*", 
John> SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}"
John> KERNEL="nst*[0-9]", ENV{ID_SERIAL}="?*", 
John> SYMLINK+="tape/by-id/$env{ID_VENDOR}-$env{ID_MODEL}-$env{ID_SERIAL_SHORT}-nst"

John> # by-path (shortest physical path)
John> KERNEL="st*[0-9]", IMPORT{program}="path_id %p"
John> KERNEL="st*[0-9]", ENV{ID_PATH}="?*", 
John> SYMLINK+="tape/by-path/$env{ID_PATH}"

John> LABEL="persistent_storage_tape_end"

John> --
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