Thread: Linux device files

Hi,

Is there a limit to how many times you can open or write to a device file? I have a program which is a continuous loop and is always writing or reading an I2C device file. After about the 1000th time it fails to open the device.

Anybody have an idea?

Here's the code:

Code:

/************************************************************************/
/* read_ad								*/
/* inputs: I2C address to write to (addr)				*/
/* outputs: Reading from the A/D in hex (ad_output)			*/
/* descritpion: Reads I2C A/D chip		*/
/************************************************************************/
int read_ad(char addr){

	sprintf(filename, "/dev/i2c-%d", adapter_nr);
	if ((file = open(filename,O_RDWR)) < 0) 
	{
		printf("Error openning device file in read_ad()\n");
		exit(1);
	}
		else{
		//printf("Device file opened\n");
		}
	
	if (ioctl(file,I2C_SLAVE,addr) < 0) 
	{
		printf("Error with ioctl function in read()\n");
		exit(1);
	}
		
  	if (read(file,ad_output,2) != 2) 
	{
    		printf("Error reading A/D chip\n");
  	}
		else{
		printf("Device file (A/D chip) reads %x\n", ad_output[0]);
		}

}

Code:

ulimit -aH

will show you the current hard limit for open files (file descriptors).

If error checking shows that is the problem you can :

Edit /etc/security/limits.conf and add the lines:

* soft nofile 1024
* hard nofile 65535

Edit /etc/pam.d/login, adding the line:

session required /lib/security/pam_limits.so

The system file descriptor limit is set in
/proc/sys/fs/file-max.

This will increase the limit to 65535:

echo 65535 > /proc/sys/fs/file-max

Then increase the file descriptor limits for the process

[quote[ulimit -n unlimited[/quote]

(--- after you log out and then back in.)

The command will set the limits to the hard limit in /etc/security/limits.conf.

You really should consider a different program design - maybe forking some new processes, or closing and reusing fd's. Using 65335 for file limit is usually not a good idea system-wide.

Thanks for the reply guys,

I went back and closed the file I opened and it seems to work.

Thanks for the help.