On 11/22/06, Keppler Alecrim <alecrim@xxxxxxxxx> wrote:
Is buf always large enough?
What happens when I do something like this?:
#define MSIZE 4
int fd;
char mbuf[MSIZE];
fd=open(modname, O_RDONLY);
read(fd, mbuf, MSIZE);
AFAIK, using the proc_read mechanism is not safe. Suppose that
your module gets rmmod-ed when some process is inside your
proc_read(). Kernel panics on return.
A safe way is to use create_proc_entry() and then set proc_fops
member of the returned struct proc_dir_entry.
The proc_fops is of type struct file_operations. It is enough
to implement the open(), read(), and release() functions.
Inside the open(), you would call try_module_get(THIS_MODULE).
Inside the release(), you would call module_put(). This way,
the rmmod would not succeed if there was a process reading
your proc file.
Hi all ,
I created a simple module to measure boot time,that is loaded on last run level of my machine. Any comment about the code or a better way?
thanks ;)
static int proc_read ( char *buf, char **start, off_t off, int count )
{
int len;
unsigned long jiffiesinit,freq;
len = 0;
jiffiesinit=INITIAL_JIFFIES;
freq=HZ;
len += sprintf (buf+len, "timestamp-cpu freq (HZ) = %lu \n",freq);
len += sprintf (buf+len, "timestamp-jiffies init= %lu \n",jiffiesinit);
len += sprintf( buf+len, "timestamp-jiffies end = %lu \n", jiffiesend );
len += sprintf( buf+len, "timestamp-jiffies diff= %lu \n", (jiffiesend-jiffiesinit) );
len += sprintf (buf+len, "timestamp-boot time in sec = %lu \n",((jiffiesend-jiffiesinit)/freq) );
return len;
}
Is buf always large enough?
What happens when I do something like this?:
#define MSIZE 4
int fd;
char mbuf[MSIZE];
fd=open(modname, O_RDONLY);
read(fd, mbuf, MSIZE);
int init_module( void )
{
printk( "<1>\nInstalling \'%s\' module\n", modname );
jiffiesend=jiffies;
create_proc_info_entry( modname, 0, NULL, proc_read );
return 0; //SUCCESS
}
AFAIK, using the proc_read mechanism is not safe. Suppose that
your module gets rmmod-ed when some process is inside your
proc_read(). Kernel panics on return.
A safe way is to use create_proc_entry() and then set proc_fops
member of the returned struct proc_dir_entry.
The proc_fops is of type struct file_operations. It is enough
to implement the open(), read(), and release() functions.
Inside the open(), you would call try_module_get(THIS_MODULE).
Inside the release(), you would call module_put(). This way,
the rmmod would not succeed if there was a process reading
your proc file.
BlackHole
