Get Major number from shell script

answerme · 05-18-2015, 11:24 PM

Hi All
I have made sample test driver for linux. Now I want to do insmod & mknod using shell script.In my shell script I am able to insert the module (i.e. insmod), but not able to do mknod because I am not able to get major number value. I print the variable major but it is blank .
By doing cat /proc/devices major number exist. But in awk command I am doing something wrong which I am unable to find out. Down is the source for script .

Code:

#!/bin/sh
module="char-dev-reg"
device="char-dev-reg"
mode="664"


/sbin/insmod ./$module.ko $* || exit 1 //insmod happing

# remove stale nodes
rm -f /dev/${device}[0-3]

major=$(awk "\$2==\"$module\" {print \$1}" /proc/devices)
echo "major='$major'"          //HERE MAJOR VALUE IS BLANK
echo "module='$module'"

mknod /dev/${device} c ${major} 0

rtmistler · 05-19-2015, 06:23 AM

Not an awk expert, or even competant at it, however I know of no device named "char-dev-reg". Like for me the type of devices I make nodes for would be ttyUSB and in my /proc/devices file I have a line saying:

Code:

188 ttyUSB

so I would be searching for that exact string.

When your module is inserted, what line does show up in your /proc/devices file? Show that line and even given my lack of awk experience, someone else who does have good awk experience can probably help you with your setting of the major mode.

pan64 · 05-19-2015, 06:28 AM

// cannot be used as comment sign in shells, you should use # instead

rtmistler · 05-19-2015, 06:34 AM

Quote:

Originally Posted by pan64

// cannot be used as comment sign in shells, you should use # instead

I think that's just a comment within their code block and not really in their shell. Instead just the point they're identifying where they've detected the variable is not the expected value.

rtmistler · 05-19-2015, 06:38 AM

@answerme your awk works. I cut back the script to just "search" and changed the module to be ttyUSB which I have in my system:

Code:

#!/bin/sh
module="ttyUSB"
major=$(awk "\$2==\"$module\" {print \$1}" /proc/devices)
echo "major='$major'"
echo "module='$module'"

The result when I ran it showed:

Code:

major='188'
module='ttyUSB'

Which is a correct result.

I'd re-check the /proc/devices file after you insert that module.

Why are you doing the "rm -f /dev/${device}[0-3]"? Maybe comment out that line for now? How do you know at that point it would be a stale device?