/proc/devices related query.

[amith <amith@xxxxxxxxxxxxxxx>]

hi all,
        there seems to be a problem with kernel version 2.4-18, 
regarding the displaying of registered char devices. If i register a 
module which registers itself with an unused major number (200 in the 
below case)and the file_operations table being NULL , i don't see the 
device major number and the corresponding name "sleeper" when i "cat 
/proc/devices".

/* init_module shown below */


#define MAJOR_NUMBER 200   
int
init_module(void)
{       int ret ;  
    ret = register_chrdev(MAJOR_NUMBER,"sleeper",NULL);
   if(ret < 0)
   {
       printk("<1> Could not register device \n");
       return 1;
   }
       printk("<1> SLEEPER registered successfully \n");   
   return 0;
}

i followed up the callback which gets called when the /proc/devices is 
read , whichled me to int get_device_list(char * page) in fs/devices.c.

There, i saw that it wasn't adding to the display buffer , those module 
names whosefile_operations table was NULL. And if someone, now insmod'ed 
a module which inturnregisters a device major number 200 (after looking 
at /proc/devices and assuming no other module is using that device major 
number ) , it would overwrite my modules file_operations(which is NULL) 
and name which is "sleeper", with its f_ops and
name in :
static struct device_struct chrdevs[MAX_CHRDEV];

<snip> (from fs/devices.c)

static struct device_struct chrdevs[MAX_CHRDEV];

int get_device_list(char * page)
{
   int i;
   int len;

   len = sprintf(page, "Character devices:\n");
   read_lock(&chrdevs_lock);
   for (i = 0; i < MAX_CHRDEV ; i++) {
       //if (chrdevs[i].fops) { // ORIGINAL CODE
       if (chrdevs[i].fops || chrdevs[i].name ) { // changed by me
             len += sprintf(page+len, "%3d %s\n", i, chrdevs[i].name);
       }
   }
   read_unlock(&chrdevs_lock);
   len += get_blkdev_list(page+len);
   return len;
}

</snip>

To conclude, it doesnt make sense to register a char device without any 
file_op's defined on it (or does it ??? ) , still, if someone using it 
for testing purposes might get confused with such a situation, where 
/proc/devices doesnt show the module registered with a  major number, 
since f_ops was NULL.

Comments welcome.

cheers,
Amith

PS: After making the above changes and re-compiling the kernel , i could 
see my module registered with the major number 200.
And i would like to know  where , such observations can be reported or 
whether they were  reported earlier.




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