Counting system calls - c

Question

I have this .c file that counts the system calls that linux calls. These are just the main functions. There were a couple of other things that I had to do, like create an array
unsigned long syscall_counts[345];
and then in another file with some assembly I incremented the array with the command:
incl syscall_counts(,%eax,4)
// This function is called each time the application calls read(). It starts the process of
// accumulating data to fill the application buffer. Return a pointer representing the current
// item. Return NULL if there are no more items.
//
static void *counter_seq_start(struct seq_file *s, loff_t *record_number)
{
if (*record_number > 347)
return NULL;
return (void*)s;
}
// This function is called to compute the next record in the sequence given a pointer to the
// current record (in bookmark). It returns a pointer to the new record (essentially, an updated
// bookmark) and updates *record_number appropriately. Return NULL if there are no more items.
//
static void *counter_seq_next(struct seq_file *s, void *bookmark, loff_t *record_number)
{
unsigned long *temp_b =(unsigned long*) bookmark;
(*temp_b)++;
if (*temp_b > 345)
return NULL;
return (void*)temp_b;
}
// This function is called whenever an application buffer is filled (or when start or next
// returns NULL. It can be used to undo any special preparations done in start (such as
// deallocating auxillary memory that was allocated in start. In simple cases, you often do not
// need to do anything in this function.
//
static void counter_seq_stop(struct seq_file *s, void *bookmark)
{
}
// This function is called after next to actually compute the output. It can use various seq_...
// printing functions (such as seq_printf) to format the output. It returns 0 if successful or a
// negative value if it fails.
//
static int counter_seq_show(struct seq_file *s, void *bookmark)
{
loff_t *bpos = (loff_t *) bookmark;
seq_printf(s, "value: %Ld\n", *bpos);
return 0;
}
// Define the only file handling function we need.
static int counter_open(struct inode *inode, struct file *file)
{
return seq_open(file, &counter_seq_ops);
}
my output is very strange:
Anyone have any idea where the issue is?

Answer 1

Don't you think :
static int counter_seq_show(struct seq_file *s, void *bookmark) {
unsigned long *bpos = (unsigned long *) bookmark;
seq_printf(s, "value: %Ld\n", *bpos);
return 0;
}
Or even
static int counter_seq_show(struct seq_file *s, void *bookmark) {
seq_printf(s, "value: %lu\n", *((unsigned long *)bpos));
return 0;
}
I haven't fully understood your program but I saw two different ways you cast 'bookmark'. In one function you cast it to be 'unsigned long *' and other you do 'loff_t *' (long int). Ideally they should be the same, but are you doing it this way for some reason ?
HTH