Bubblesort on singly linked lists

bubblelist.c

/* bubble sort a linked list */
#include <stdio.h>
#include <stdlib.h>

static struct list *scan_list(void);
static void sort_list(struct list **);
static void print_list(struct list *);
static void free_list(struct list *);

struct list {
	struct list *next;
	int elem;
};

int main()
{
	struct list *l = scan_list();

	sort_list(&l);
	print_list(l);
	free_list(l);
}

static struct list *
scan_list(void)
{
	struct list *l = NULL, **cell = &l;
	int val;

	while (scanf("%d", &val) == 1) {
		*cell = malloc(sizeof **cell);
		if (*cell == NULL) {
			perror("malloc");
			exit(EXIT_FAILURE);
		}

		(*cell)->next = NULL;
		(*cell)->elem = val;
		cell = &(*cell)->next;
	}

	return (l);
}

static void
print_list(struct list *l)
{
	while (l != NULL) {
		printf("%d\n", l->elem);
		l = l->next;
	}
}

static void
free_list(struct list *l)
{
	struct list *ll;

	while (l != NULL) {
		ll = l->next;
		free(l);
		l = ll;
	}
}

/* sort list using bubble sort */
static void
sort_list(struct list **l)
{
	int swap;
	struct list **i, *a, *b;

	do {
		swap = 0;
		for (i = l; *i != NULL && (*i)->next != NULL; i = &(*i)->next)
			if ((*i)->elem > (*i)->next->elem) {
				swap = 1;
				a = *i;
				b = (*i)->next;
				a->next = b->next;
				b->next = a;
				*i = b;
			}
	} while (swap);
}