Started implementing backing managment

src/backing.c

@@ -0,0 +1,63 @@
+#include "backing.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+bool is_valid_backing_id(const char* backing_id) {
+	if (backing_id == NULL)
+		return false;
+
+	size_t length = strlen(backing_id);
+
+	// Check that the length is valid
+	if (length == 0 || length > MAX_BACKING_LENGTH)
+		return false;
+
+	// Check that the backing id does not contain any slashes
+	for (size_t i = 0; i < length; i++)
+		if (backing_id[i] == '/')
+			return false;
+
+	// Check that the backing id is not a reserved name
+	if (strcmp(backing_id, ".") == 0 || strcmp(backing_id, "..") == 0)
+		return false;
+
+	return true;
+}
+
+Result get_backing_path(const char* backing_id, char** out_path) {
+	*out_path = NULL;
+
+	// Check that the backing id is valid
+	if (!is_valid_backing_id(backing_id)) {
+		log_message(LOG_LEVEL_ERROR, "Invalid backing id '%s'.", backing_id);
+		return FAILURE;
+	}
+
+	return format(out_path, "%s/%s", BACKING_POOL_DIR, backing_id);
+}
+
+Result backing_exists(const char* backing_id, bool* out_exists) {
+	*out_exists = false;
+
+	// Get the path of the backing
+	char* path;
+	Result result = get_entry_path(backing_id, &path);
+	if (result != SUCCESS)
+		return result;
+
+	// Check if the backing exists and is a file
+	struct stat st;
+	bool exists = stat(path, &st) == 0 && S_ISREG(st.st_mode);
+
+	// Free the path
+	free(path);
+
+	// Output the result
+	*out_exists = exists;
+
+	return SUCCESS;
+}