[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/config/fault.h

@@ -0,0 +1,19 @@
+#ifndef CONFIG_FAULT_H
+#define CONFIG_FAULT_H
+
+/** @file
+ *
+ * Fault injection
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <config/defaults.h>
+
+/* Drop every N transmitted or received network packets */
+#define	NETDEV_DISCARD_RATE 0
+
+#include <config/local/fault.h>
+
+#endif /* CONFIG_FAULT_H */

src/config/general.h

@@ -156,7 +156,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
-#define	NETDEV_DISCARD_RATE 0	/* Drop every N packets (0=>no drop) */
 #undef	BUILD_SERIAL		/* Include an automatic build serial
 				 * number.  Add "bs" to the list of
 				 * make targets.  For example:

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;
+}

src/include/ipxe/errfile.h

@@ -68,6 +68,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_fbcon		       ( ERRFILE_CORE | 0x001c0000 )
 #define ERRFILE_ansicol		       ( ERRFILE_CORE | 0x001d0000 )
 #define ERRFILE_ansicoldef	       ( ERRFILE_CORE | 0x001e0000 )
+#define ERRFILE_fault		       ( ERRFILE_CORE | 0x001f0000 )
 
 #define ERRFILE_eisa		     ( ERRFILE_DRIVER | 0x00000000 )
 #define ERRFILE_isa		     ( ERRFILE_DRIVER | 0x00010000 )

src/include/ipxe/fault.h

@@ -0,0 +1,32 @@
+#ifndef _IPXE_FAULT_H
+#define _IPXE_FAULT_H
+
+/** @file
+ *
+ * Fault injection
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <config/fault.h>
+
+extern int inject_fault_nonzero ( unsigned int rate );
+
+/**
+ * Inject fault with a specified probability
+ *
+ * @v rate		Reciprocal of fault probability (zero for no faults)
+ * @ret rc		Return status code
+ */
+static inline __attribute__ (( always_inline )) int
+inject_fault ( unsigned int rate ) {
+
+	/* Force dead code elimination in non-fault-injecting builds */
+	if ( rate == 0 )
+		return 0;
+
+	return inject_fault_nonzero ( rate );
+}
+
+#endif /* _IPXE_FAULT_H */

src/net/netdevice.c

@@ -39,6 +39,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/device.h>
 #include <ipxe/errortab.h>
 #include <ipxe/profile.h>
+#include <ipxe/fault.h>
 #include <ipxe/vlan.h>
 #include <ipxe/netdevice.h>
 
@@ -303,11 +304,8 @@ int netdev_tx ( struct net_device *netdev, struct io_buffer *iobuf ) {
 	}
 
 	/* Discard packet (for test purposes) if applicable */
-	if ( ( NETDEV_DISCARD_RATE > 0 ) &&
-	     ( ( random() % NETDEV_DISCARD_RATE ) == 0 ) ) {
-		rc = -EAGAIN;
+	if ( ( rc = inject_fault ( NETDEV_DISCARD_RATE ) ) != 0 )
 		goto err;
-	}
 
 	/* Transmit packet */
 	if ( ( rc = netdev->op->transmit ( netdev, iobuf ) ) != 0 )
@@ -457,14 +455,14 @@ static void netdev_tx_flush ( struct net_device *netdev ) {
  * function takes ownership of the I/O buffer.
  */
 void netdev_rx ( struct net_device *netdev, struct io_buffer *iobuf ) {
+	int rc;
 
 	DBGC2 ( netdev, "NETDEV %s received %p (%p+%zx)\n",
 		netdev->name, iobuf, iobuf->data, iob_len ( iobuf ) );
 
 	/* Discard packet (for test purposes) if applicable */
-	if ( ( NETDEV_DISCARD_RATE > 0 ) &&
-	     ( ( random() % NETDEV_DISCARD_RATE ) == 0 ) ) {
-		netdev_rx_err ( netdev, iobuf, -EAGAIN );
+	if ( ( rc = inject_fault ( NETDEV_DISCARD_RATE ) ) != 0 ) {
+		netdev_rx_err ( netdev, iobuf, rc );
 		return;
 	}