[fault] Generalise NETDEV_DISCARD_RATE fault injection mechanism

Provide a generic inject_fault() function that can be used to inject
random faults with configurable probabilities.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/fault.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdlib.h>
+#include <errno.h>
+#include <ipxe/fault.h>
+
+/** @file
+ *
+ * Fault injection
+ *
+ */
+
+/**
+ * Inject fault with a specified probability
+ *
+ * @v rate		Reciprocal of fault probability (must be non-zero)
+ * @ret rc		Return status code
+ */
+int inject_fault_nonzero ( unsigned int rate ) {
+
+	/* Do nothing unless we want to inject a fault now */
+	if ( ( random() % rate ) != 0 )
+		return 0;
+
+	/* Generate error number here so that faults can be injected
+	 * into files that don't themselves have error file
+	 * identifiers (via errfile.h).
+	 */
+	return -EFAULT;
+}