Re: More Elegant udev rules

Thanks Daniel

On Mon, 21 Nov 2011 09:25:26 +1300, Daniel Lawson <[email protected]>
wrote:
>> I found the following udev rules on the citrix forums designed to expose
>> hard drive devices to VMs. By adding these rules to 50-udev.rules it does
>> the job but exposes a bunch of other rubbish I could do without.
>>
>>
>>
>> ACTION=="add", SYSFS{vendor}=="ATA     ",
>> ID=="1:0:0:0|2:0:0:0|3:0:0:0|4:0:0:0",
>>
>> SYMLINK+="xapi/block/%k", \
>>
>> RUN+="/bin/sh -c '/opt/xensource/libexec/local-device-change %k 2>&1
>>> /dev/null&'"
>> ACTION=="remove", SYSFS{vendor}=="ATA     ",
>> ID=="1:0:0:0|2:0:0:0|3:0:0:0|4:0:0:0", \
>>
>> RUN+="/bin/sh -c '/opt/xensource/libexec/local-device-change %k 2>&1
>>> /dev/null&'"
>>
>>
>> Can anyone see how I could alter these rules to only expose my 3 2Tb Seagate
>> sata drives?
> 
> Yes, you can use one of the sysfs variables to limit on the specific
> serial number of the drive. Or you could limit it to a model number,
> or manufacturer, etc
> 
> In the "ACTION" line, it currently selects based on the SYSFS{vendor}
> variable being "ATA     ", you could change that to SYSFS{serial} =
> "yourserial". Get the serial number via sysfs itself to make sure
> you're referring to the right thing
> 
I had considered that but was more looking for code that would work in
all instances instead of a specific instance.
Not being a programmer I can't fully comprehend why the combination of
SYSFS{vendor} and ID doesn't isolate devices more than it seems to
already.
Literally hundreds of devices appear in the removable storage list
using the above code.
> 
>> And while we are at it, is there a way to use IOCTL or hdparm
>> within the rules to turn write cache off on each of my three drives without
>> turning it off on the drive holding the system? (a completely separate
>> drive, SSD in this case, which is also exposed to the VMs by the above
>> rules)
> 
> You already run a script in that rule on add/remove events. You could
> either modify that script or write a new wrapper script that calls
> your hdparm command and then calls the local-device-change script. Or
> maybe the semantics of the RUN command allow multiple RUN lines, I
> can't recall.

Thanks,  I'm a little worried about the warning to not run long running
tasks using RUN. To make this elegant I would need to run hdparm on all
possible hard disk devices. As part of a wrapper script would this be
regarded as long?

> 
> Either way, reading the udev manuals will help you a lot.

I have read and re-read this site
http://reactivated.net/writing_udev_rules.html and tried to understand
the man pages prior to asking for help.
My lack of programming knowledge is restricting my progress.
I'm sorry I'm a real novice, particularly at low level interactions
with hardware.
Can anyone point me to a link better addressing the specific example
with respect to udev rules writing?

> 
> 
> 
> 
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