Started reimplementing some functions for the backing system

src/backing.c

@@ -0,0 +1,74 @@
+#include "backing.h"
+
+#include <string.h>
+#include <sys/stat.h>
+
+bool is_valid_backing_name(const char* name) {
+	if (name == NULL)
+		return false;
+
+	size_t len = strlen(name);
+	if (len == 0)
+		return false;
+
+	for (size_t i = 0; i < len; i++)
+		if (name[i] == '/')
+			return false;
+
+	if (name[0] < '0' || name[0] > '9')
+		return false;
+
+	return true;
+}
+
+char* get_backing_path(const char* name) {
+	if (name == NULL)
+		return NULL;
+
+	return format("%s/%s", "/var/lib/sandbox/backings", name);
+}
+
+bool backing_exists(const char* name) {
+	if (name == NULL)
+		return false;
+
+	char* path = get_backing_path(name);
+	if (path == NULL)
+		return false;
+
+	// Check if the backing exists
+	struct stat st;
+	if (stat(path, &st) != 0) {
+		free(path);
+		return false;
+	}
+
+	// Free the path, as it is no longer needed
+	free(path);
+
+	if (!S_ISREG(st.st_mode))
+		return false;
+
+	return true;
+}
+
+time_t get_backing_ctime(const char* name) {
+	// As the name starts with the ctime, we can just convert the first part of the name to a time_t
+	size_t len = strlen(name);
+	size_t ctime_len = 0;
+	for (size_t i = 0; i < len; i++) {
+		if (name[i] < '0' || name[i] > '9')
+			break;
+
+		ctime_len++;
+	}
+
+	char* ctime_str = strndup(name, ctime_len);
+	if (ctime_str == NULL)
+		return 0;
+
+	time_t ctime = (time_t)strtoull(ctime_str, NULL, 10);
+	free(ctime_str);
+
+	return ctime;
+}