can't open device file after called?

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After i create device file by calling device_create:

device_create(test_class, parent, devt, test_dev, "%s", "test")

i can list test file device when using ls command
# ls -l /dev/test
but when i using command:
# cat /dev/test
i get an error:
couldn't found '/dev/test' or address

Please explain for me how to solve that problem, thank so much!

Posted 2-Jul-12 20:04pm

mot sach

Updated 2-Jul-12 20:33pm

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Richard MacCutchan 3-Jul-12 4:17am

Please show the actual output of the ls and cat commands, not your interpretation of what you think they said.

mot sach 4-Jul-12 3:42am

sorry, this is out put:
# ls -l /dev/test
output:
/dev/test

# cat /dev/test
output:
cat: can't open '/dev/test': No such device or address

i really don't understand difference between calling device_create function and mknod command

Richard MacCutchan 4-Jul-12 4:05am

If that is all you are getting from ls -l then there is something wrong as your device has no connection to anything, it's just a name. If you do not understand device_create then I recommend reading the man pages and doing some Google research.

mot sach 8-Jul-12 23:54pm

this is my source code:

#define DBG_MSG(msg) printk(KERN_INFO "[test] %s %s\n", __FUNCTION__, msg)

struct class* test_class;
dev_t devt;
struct device* dev;
static int __init test_init(void)
{
DBG_MSG("enter");
test_class = class_create(THIS_MODULE, "test_class");
if ( IS_ERR(test_class) ) {
printk ( "can't create test class\n" );
class_destroy(test_class);
return PTR_ERR(test_class);
}
//register test device
major = register_chrdev(FPGA_DYNAMIC_MAJOR, "test", &test_fops);
printk ( "[test] %d\n", major );
devt = MKDEV(major, 0);
dev = device_create(test_class, NULL, devt, NULL, "test");
device_register(dev);
DBG_MSG("exit succesfull");
return 0;
}

after installed modules, and called mdev -s command, i can read /sys/class/test_class/test/dev, but i can't read /dev/test. Could you help me solve this problem? Thank so much!

Richard MacCutchan 9-Jul-12 4:10am

I already told you: /dev/test does not have a proper entry in the device table - you need to correct it so it is linked to a real device.

mot sach 10-Jul-12 21:51pm

yeah, could you suggest for me how to solve that (sorry because i am newbie), ^_^.

Richard MacCutchan 11-Jul-12 3:03am

Probably by the ln (link) command; it's a while since I did this on Linux.

You say you are a newbie, in which case, I strongly suggest you get hold of a good book on Linux and study the subject you are working on. You will never get to be an expert by asking piecemeal questions on forums like this.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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