[PATCH 3/3] xen blkback: add fault injection facility

[Stanislav Kinsburskii <staskins@amazon.com>]

This patch adds wrapper helpers around generic Xen fault inject
facility.
The major reason is to keep all the module fault injection directories
in a dedicated subdirectory instead of Xen fault inject root.

IOW, when using these helpers, per-device and named by device name
fault injection control directories will appear under the following
directory:
- /sys/kernel/debug/xen/fault_inject/xen-blkback/
instead of:
- /sys/kernel/debug/xen/fault_inject/

Signed-off-by: Stanislav Kinsburskii <staskins@amazon.com>
CC: Jens Axboe <axboe@kernel.dk>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: "Roger Pau Monné" <roger.pau@citrix.com>
CC: linux-kernel@vger.kernel.org
CC: linux-block@vger.kernel.org
CC: xen-devel@lists.xenproject.org
CC: Stanislav Kinsburskii <staskins@amazon.com>
CC: David Woodhouse <dwmw@amazon.co.uk>
---
 drivers/block/Kconfig                  |    7 ++
 drivers/block/xen-blkback/Makefile     |    1 
 drivers/block/xen-blkback/blkback.c    |    9 ++
 drivers/block/xen-blkback/blkback_fi.c |  116 ++++++++++++++++++++++++++++++++
 drivers/block/xen-blkback/blkback_fi.h |   37 ++++++++++
 drivers/block/xen-blkback/common.h     |    3 +
 drivers/block/xen-blkback/xenbus.c     |    5 +
 7 files changed, 178 insertions(+)
 create mode 100644 drivers/block/xen-blkback/blkback_fi.c
 create mode 100644 drivers/block/xen-blkback/blkback_fi.h

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index ad9b687..0ce05fe 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -436,6 +436,13 @@ config XEN_BLKDEV_BACKEND
 	  compile this driver as a module, chose M here: the module
 	  will be called xen-blkback.
 
+config XEN_BLKDEV_BACKEND_FAULT_INJECTION
+	  bool "Xen block-device backend driver fault injection"
+	  depends on XEN_BLKDEV_BACKEND
+	  depends on XEN_FAULT_INJECTION
+	  default n
+	  help
+	    Allow to inject errors to Xen backend block driver
 
 config VIRTIO_BLK
 	tristate "Virtio block driver"
diff --git a/drivers/block/xen-blkback/Makefile b/drivers/block/xen-blkback/Makefile
index e491c1b..035d134 100644
--- a/drivers/block/xen-blkback/Makefile
+++ b/drivers/block/xen-blkback/Makefile
@@ -1,3 +1,4 @@
 obj-$(CONFIG_XEN_BLKDEV_BACKEND) := xen-blkback.o
 
 xen-blkback-y	:= blkback.o xenbus.o
+xen-blkback-$(CONFIG_XEN_BLKDEV_BACKEND_FAULT_INJECTION) += blkback_fi.o
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 987d665..2933bec 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -51,6 +51,7 @@
 #include <xen/balloon.h>
 #include <xen/grant_table.h>
 #include "common.h"
+#include "blkback_fi.h"
 
 /*
  * Maximum number of unused free pages to keep in the internal buffer.
@@ -1491,11 +1492,19 @@ static int __init xen_blkif_init(void)
 	if (rc)
 		goto failed_init;
 
+	(void) xen_blkbk_fi_init();
  failed_init:
 	return rc;
 }
 
 module_init(xen_blkif_init);
 
+static void __exit xen_blkif_fini(void)
+{
+	xen_blkbk_fi_fini();
+}
+
+module_exit(xen_blkif_fini);
+
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("xen-backend:vbd");
diff --git a/drivers/block/xen-blkback/blkback_fi.c b/drivers/block/xen-blkback/blkback_fi.c
new file mode 100644
index 0000000..b7abaea
--- /dev/null
+++ b/drivers/block/xen-blkback/blkback_fi.c
@@ -0,0 +1,116 @@
+/*
+ * Fault injection interface for Xen virtual block devices
+ *
+ * Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <linux/slab.h>
+#include <linux/debugfs.h>
+
+#include <xen/fault_inject.h>
+
+#include "blkback_fi.h"
+#include "common.h"
+
+static struct dentry *blkif_fi_dir;
+
+static const char *xen_blkif_fi_names[XENBLKIF_FI_MAX] = {
+};
+
+struct xen_blkif_fi {
+	struct dentry *dir;
+	struct xen_fi *faults[XENBLKIF_FI_MAX];
+};
+
+int xen_blkbk_fi_init(void)
+{
+	blkif_fi_dir = xen_fi_dir_create("xen-blkback");
+	if (!blkif_fi_dir)
+		return -ENOMEM;
+	return 0;
+}
+
+void xen_blkbk_fi_fini(void)
+{
+	debugfs_remove_recursive(blkif_fi_dir);
+}
+
+void xen_blkif_fi_fini(struct xen_blkif *blkif)
+{
+	struct xen_blkif_fi *bfi = blkif->fi_info;
+	int fi;
+
+	if (!blkif->fi_info)
+		return;
+
+	blkif->fi_info = NULL;
+
+	for (fi = 0; fi < XENBLKIF_FI_MAX; fi++)
+		xen_fi_del(bfi->faults[fi]);
+	debugfs_remove_recursive(bfi->dir);
+	kfree(bfi);
+}
+
+int xen_blkif_fi_init(struct xen_blkif *blkif)
+{
+	struct xen_blkif_fi *bfi;
+	int fi, err = -ENOMEM;
+
+	bfi = kmalloc(sizeof(*bfi), GFP_KERNEL);
+	if (!bfi)
+		return -ENOMEM;
+
+	bfi->dir = debugfs_create_dir(dev_name(&blkif->be->dev->dev),
+				      blkif_fi_dir);
+	if (!bfi->dir)
+		goto err_dir;
+
+	for (fi = 0; fi < XENBLKIF_FI_MAX; fi++) {
+		bfi->faults[fi] = xen_fi_dir_add(bfi->dir,
+						 xen_blkif_fi_names[fi]);
+		if (!bfi->faults[fi])
+			goto err_fault;
+	}
+
+	blkif->fi_info = bfi;
+	return 0;
+
+err_fault:
+	for (; fi > 0; fi--)
+		xen_fi_del(bfi->faults[fi]);
+	debugfs_remove_recursive(bfi->dir);
+err_dir:
+	kfree(bfi);
+	return err;
+}
+
+bool xenblkif_should_fail(struct xen_blkif *blkif, xen_blkbk_fi_t type)
+{
+	struct xen_blkif_fi *bfi = blkif->fi_info;
+
+	return xen_should_fail(bfi->faults[type]);
+}
diff --git a/drivers/block/xen-blkback/blkback_fi.h b/drivers/block/xen-blkback/blkback_fi.h
new file mode 100644
index 0000000..4e29850
--- /dev/null
+++ b/drivers/block/xen-blkback/blkback_fi.h
@@ -0,0 +1,37 @@
+#ifndef _XEN_BLKBACK_FI_H
+#define _XEN_BLKBACK_FI_H
+
+struct xen_fi;
+struct xen_blkif;
+
+typedef enum {
+	XENBLKIF_FI_MAX
+} xen_blkbk_fi_t;
+
+#ifdef CONFIG_XEN_BLKDEV_BACKEND_FAULT_INJECTION
+
+void xen_blkbk_fi_fini(void);
+int xen_blkbk_fi_init(void);
+
+void xen_blkif_fi_fini(struct xen_blkif *blkif);
+int xen_blkif_fi_init(struct xen_blkif *blkif);
+
+bool xenblkif_should_fail(struct xen_blkif *blkif, xen_blkbk_fi_t type);
+
+#else
+
+static inline void xen_blkbk_fi_fini(void) { }
+static inline int xen_blkbk_fi_init(void) { return 0; }
+
+static inline void xen_blkif_fi_fini(struct xen_blkif *blkif) { }
+static inline int xen_blkif_fi_init(struct xen_blkif *blkif) { return 0; }
+
+static inline bool xenblkif_should_fail(struct xen_blkif *blkif, xen_blkbk_fi_t type)
+{
+	return false;
+}
+
+#endif /* CONFIG_XEN_BLKDEV_BACKEND_FAULT_INJECTION */
+
+#endif /* _XEN_BLKBACK_FI_H */
+
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index ecb35fe..6d12d4d 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -329,6 +329,9 @@ struct xen_blkif {
 	/* All rings for this device. */
 	struct xen_blkif_ring	*rings;
 	unsigned int		nr_rings;
+#ifdef CONFIG_XEN_BLKDEV_BACKEND_FAULT_INJECTION
+	void			*fi_info;
+#endif
 };
 
 struct seg_buf {
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 21c1be1..9931fc8 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -22,6 +22,7 @@
 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include "common.h"
+#include "blkback_fi.h"
 
 /* On the XenBus the max length of 'ring-ref%u'. */
 #define RINGREF_NAME_LEN (20)
@@ -246,6 +247,8 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 	unsigned int j, r;
 	bool busy = false;
 
+	xen_blkif_fi_fini(blkif);
+
 	for (r = 0; r < blkif->nr_rings; r++) {
 		struct xen_blkif_ring *ring = &blkif->rings[r];
 		unsigned int i = 0;
@@ -998,6 +1001,8 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
 		return err;
 	}
 
+	(void) xen_blkif_fi_init(blkif);
+
 	return 0;
 
 fail:

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