btrfs-progs: add simple error injection framework

To be able to test errors at specific locations, add a simple way to
check for a condition in code and controlled from user space environment
variable INJECT. For now a single value is accepted.

Use like:

	if (inject_error(0x1234)) {
		do_something();
		return -ERROR;
	}

This is enabled in debugging build by default (make D=1) and can be
enabled on demand too (make EXTRA_CFLAGS=-DINJECT).

Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -67,7 +67,7 @@ include Makefile.extrawarn
 EXTRA_CFLAGS :=
 EXTRA_LDFLAGS :=
 
-DEBUG_CFLAGS_DEFAULT = -O0 -U_FORTIFY_SOURCE -ggdb3
+DEBUG_CFLAGS_DEFAULT = -O0 -U_FORTIFY_SOURCE -ggdb3 -DINJECT
 DEBUG_CFLAGS_INTERNAL =
 DEBUG_CFLAGS :=
 
@@ -202,6 +202,7 @@ objects = \
 	common/format-output.o	\
 	common/fsfeatures.o	\
 	common/help.o	\
+	common/inject-error.o	\
 	common/messages.o	\
 	common/open-utils.o	\
 	common/parse-utils.o	\

common/inject-error.c

@@ -0,0 +1,88 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * 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., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+/*
+ * Simple error injection framework. Enabled at build time by -DINJECT.
+ */
+
+#include "inject-error.h"
+
+#ifdef INJECT
+
+static bool inject_verbose = true;
+
+static bool cookie_enabled(unsigned long cookie) {
+	const char *inj = getenv("INJECT");
+	unsigned long envcookie;
+
+	if (inj == NULL || inj[0] == 0)
+		return false;
+
+	envcookie = strtoul(inj, NULL, 0);
+	if (envcookie == cookie)
+		return true;
+	return false;
+}
+
+#define inject_error(cookie)	__inject_error((cookie), __FILE__, __LINE__)
+
+bool __inject_error(unsigned long cookie, const char *file, int line) {
+	if (cookie == 0x0) {
+		fprintf(stderr, "Error injection testing cookie 0x0\n");
+		return true;
+	}
+
+	if (cookie_enabled(cookie)) {
+		if (inject_verbose)
+			fprintf(stderr, "Error injection: cookie 0x%lx in %s:%d\n",
+				cookie, file, line);
+		return true;
+	}
+
+	return false;
+}
+
+#else
+
+#define inject_error(cookie)		(false)
+
+#endif
+
+#ifdef DEMO
+#include <unistd.h>
+/* gcc -o inject-error inject-error.c -DDEMO */
+int work(int x) {
+	sleep(1);
+	printf("x=%d\n", x);
+	if (x == 3 && inject_error(0x03)) {
+		printf("error injected\n");
+		return -1;
+	}
+	return 0;
+}
+
+int main() {
+	int ret = 0;
+	int x = 1;
+
+	printf("Injection: INJECT=%s\n", getenv("INJECT"));
+	while (ret == 0) {
+		ret = work(x);
+		x++;
+	}
+	return 0;
+}
+#endif

common/inject-error.h

@@ -0,0 +1,35 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * 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., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#ifndef __INJECT_ERROR_H__
+#define __INJECT_ERROR_H__
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+
+#ifdef INJECT
+
+#define inject_error(cookie)	__inject_error((cookie), __FILE__, __LINE__)
+bool __inject_error(unsigned long cookie, const char *file, int line);
+
+#else
+
+#define inject_error(cookie)		(false)
+
+#endif
+
+#endif