Add debugging messages about truncation and seeking (#45).

src/pv/state.c

@@ -276,6 +276,8 @@ static void pv_truncate_output(pvstate_t state)
 	if (current_offset == (off_t) - 1)
 		return;
 
+	debug("%s: %ld", "truncating to current offset", (long) current_offset);
+
 	if (0 != ftruncate(state->control.output_fd, current_offset)) {
 		debug("%s: %s", "output ftruncate() failed", strerror(errno));
 	}

src/pv/transfer.c

@@ -711,6 +711,8 @@ static int pv__transfer_write(pvstate_t state, bool *eof_in, bool *eof_out, long
 					state->transfer.output_not_seekable = true;
 				} else {
 					/* Seek successful - skip write. */
+					debug("%s (%ld) -> %s: %ld", "skipped null writes",
+					      (long) (state->transfer.to_write), "new position", (long) output_offset);
 					nwritten = state->transfer.to_write;
 					goto pv__transfer_write_completed;
 				}