-/* Read LEN bytes at PTR from descriptor DESC, for file FILENAME,
- retrying if necessary. Return a negative value if an error occurs,
- otherwise return the actual number of bytes read,
- which must be LEN unless end-of-file was reached. */
+/* Read LEN bytes at PTR from descriptor DESC, retrying if interrupted.
+ Return the actual number of bytes read, zero for EOF, or negative
+ for an error. */