Write an fread function for segments; use in apple2.dd

src/vm_segment.c

@@ -204,3 +204,25 @@ vm_segment_write_map(vm_segment *segment,
     segment->write_table[addr] = fn;
     return OK;
 }
+
+/*
+ * Read the given file stream and write the contents into the given
+ * segment, up to len bytes. If we could not read from the file stream
+ * for some reason, signal that and return an error.
+ */
+int
+vm_segment_fread(vm_segment *segment, FILE *stream, size_t len)
+{
+    fread(segment->memory, sizeof(vm_8bit), len, stream);
+
+    // fread() may return zero in the case of an error, but it may
+    // return a positive non-zero number short of len; we can't quite
+    // count on just that to tell us something went wrong (especially if
+    // len was not a valid length for the file to begin with).
+    if (ferror(stream)) {
+        log_critical("Could not read file stream: %s\n", strerror(errno));
+        return ERR_BADFILE;
+    }
+
+    return OK;
+}