How to make a FIFO buffer with can_frame structure inside? - c

Question

In the moment I am working on a project on which a few processors are communication between then using can bus. The main controler (beagle bone) controls the other device using a can bus. Using a socket can linux framework I wrote a proccess that reads the can messages send from the other devices, and now I want to put the messages I get into a FIFO bufer, and then to obrabotam the messages.
So I need to write the FIFO buffer with can_frame structure inside.
For example:
struct can_buffer {
struct can_frame *frames;
int head;
int tail;
int size;
};
can_buffer new_can_buffer (size_t capacity)
{
can_buffer rb = malloc(sizeof(struct can_buffer));
if (rb) {
/* One byte is used for detecting the full condition. */
rb->size = capacity + 1;
rb->frames = malloc(rb->size * sizeof(struct can_frame));
if (rb->frames)
can_buffer_reset(rb);
else {
free(rb);
return 0;
}
}
return rb;
}
size_t can_buffer_size(const struct can_buffer *rb)
{
return rb->size;
}
size_t can_buffer_capacity(const struct can_buffer *rb)
{
return can_buffer_buffer_size(rb) - 1;
}
size_t can_buffer_free(const struct can_buffer *rb)
{
if (rb->head >= rb->tail)
return can_buffer_capacity(rb) - (rb->head - rb->tail);
else
return rb->tail - rb->head - 1;
}
int can_buffer_is_full(const struct can_buffer *rb)
{
return can_buffer_free(rb) == 0;
}
int can_buffer_is_empty(const struct can_buffer *rb)
{
return can_buffer_free(rb) ==can_buffer_capacity(rb);
}
void can_buffer_reset(can_buffer rb)
{
rb->head = rb->tail = 0;
}
.........
........
/* Add message to the end of the queue. */
void can_buffer_push(struct can_buffer *cb, struct can_frame *frame)
{
memcpy(&cb->frames[cb->tail], frame, sizeof(struct can_frame));
cb->tail = (cb->tail + 1) % cb->size;
}
/* Retrieve message from the start of the queue. */
can_frame *can_buffer_pop(struct can_buffer *cb)
{
struct can_frame *frame;
memcpy(frame, &cb->frames[cb->head], sizeof(struct can_frame));
cb->head = (cb->head + 1) % cb->size;
return frame;
}
But I canoot do it successfully. I think the problem is that every can_frame structure inside is a structure again,that is the problem (for example int, char etc), but I do not know how to solve this issue.
How can I make a FIFO buffer that can store the can_frame structure inside?
I need to write this in C lagnuage
in main i call
can_buffer can_buff;
can_buff = new_can_buffer(100);
can_buffer_push(can_buff,frame);
frame = can_frame i received
can_buff = fifo buffer

Answer 1

Well, you have incompletely modified the ringbuf routines. Specifically, you don't allocate enough space for the structures here:
if (rb) {
/* One byte is used for detecting the full condition. */
rb->size = capacity + 1;
rb->frames = malloc(rb->size);
if (rb->frames)
ringbuf_reset(rb);
else {
free(rb);
return 0;
}
}
The malloc needs to be
rb->frames = malloc(rb->size * sizeof(struct can_frame));
And the you should update the ringbuf_reset() call on the next line to your renamed can_buffer_reset()
Addendum:
I just noticed that you also need to update your ringbuf_reset() function to rb->head = rb->tail = 0
Addendum 2:
Referencing the newly added code, can_buffer_pop() will not work correctly as it doesn't check for the message existing and it doesn't allocate memory for the popped message.
There is also a typo in can_buffer_capacity().
Editorial:
I would strongly suggest writing a simple test program that executes these functions. It's frustrating but will catch a number of these small gotchas.