dm: add flakey target

This target is the same as the linear target except that it returns I/O
errors periodically.  It's been found useful in simulating failing
devices for testing purposes.

I needed a dm target to do some failure testing on btrfs's raid code, and
Mike pointed me at this.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

Documentation/device-mapper/dm-flakey.txt

+dm-flakey
+=========
+
+This target is the same as the linear target except that it returns I/O
+errors periodically.  It's been found useful in simulating failing
+devices for testing purposes.
+
+Starting from the time the table is loaded, the device is available for
+<up interval> seconds, then returns errors for <down interval> seconds,
+and then this cycle repeats.
+
+Parameters: <dev path> <offset> <up interval> <down interval>
+    <dev path>: Full pathname to the underlying block-device, or a
+                "major:minor" device-number.
+    <offset>: Starting sector within the device.
+    <up interval>: Number of seconds device is available.
+    <down interval>: Number of seconds device returns errors.

drivers/md/Kconfig

@@ -327,4 +327,10 @@ config DM_UEVENT
 	---help---
 	Generate udev events for DM events.
 
+config DM_FLAKEY
+       tristate "Flakey target (EXPERIMENTAL)"
+       depends on BLK_DEV_DM && EXPERIMENTAL
+       ---help---
+         A target that intermittently fails I/O for debugging purposes.
+
 endif # MD

drivers/md/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_BLK_DEV_MD)	+= md-mod.o
 obj-$(CONFIG_BLK_DEV_DM)	+= dm-mod.o
 obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o
 obj-$(CONFIG_DM_DELAY)		+= dm-delay.o
+obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o
 obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o
 obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o
 obj-$(CONFIG_DM_MULTIPATH_ST)	+= dm-service-time.o

drivers/md/dm-flakey.c

+/*
+ * Copyright (C) 2003 Sistina Software (UK) Limited.
+ * Copyright (C) 2004, 2010 Red Hat, Inc. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/device-mapper.h>
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+
+#define DM_MSG_PREFIX "flakey"
+
+/*
+ * Flakey: Used for testing only, simulates intermittent,
+ * catastrophic device failure.
+ */
+struct flakey_c {
+	struct dm_dev *dev;
+	unsigned long start_time;
+	sector_t start;
+	unsigned up_interval;
+	unsigned down_interval;
+};
+
+/*
+ * Construct a flakey mapping: <dev_path> <offset> <up interval> <down interval>
+ */
+static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct flakey_c *fc;
+	unsigned long long tmp;
+
+	if (argc != 4) {
+		ti->error = "dm-flakey: Invalid argument count";
+		return -EINVAL;
+	}
+
+	fc = kmalloc(sizeof(*fc), GFP_KERNEL);
+	if (!fc) {
+		ti->error = "dm-flakey: Cannot allocate linear context";
+		return -ENOMEM;
+	}
+	fc->start_time = jiffies;
+
+	if (sscanf(argv[1], "%llu", &tmp) != 1) {
+		ti->error = "dm-flakey: Invalid device sector";
+		goto bad;
+	}
+	fc->start = tmp;
+
+	if (sscanf(argv[2], "%u", &fc->up_interval) != 1) {
+		ti->error = "dm-flakey: Invalid up interval";
+		goto bad;
+	}
+
+	if (sscanf(argv[3], "%u", &fc->down_interval) != 1) {
+		ti->error = "dm-flakey: Invalid down interval";
+		goto bad;
+	}
+
+	if (!(fc->up_interval + fc->down_interval)) {
+		ti->error = "dm-flakey: Total (up + down) interval is zero";
+		goto bad;
+	}
+
+	if (fc->up_interval + fc->down_interval < fc->up_interval) {
+		ti->error = "dm-flakey: Interval overflow";
+		goto bad;
+	}
+
+	if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &fc->dev)) {
+		ti->error = "dm-flakey: Device lookup failed";
+		goto bad;
+	}
+
+	ti->num_flush_requests = 1;
+	ti->private = fc;
+	return 0;
+
+bad:
+	kfree(fc);
+	return -EINVAL;
+}
+
+static void flakey_dtr(struct dm_target *ti)
+{
+	struct flakey_c *fc = ti->private;
+
+	dm_put_device(ti, fc->dev);
+	kfree(fc);
+}
+
+static sector_t flakey_map_sector(struct dm_target *ti, sector_t bi_sector)
+{
+	struct flakey_c *fc = ti->private;
+
+	return fc->start + (bi_sector - ti->begin);
+}
+
+static void flakey_map_bio(struct dm_target *ti, struct bio *bio)
+{
+	struct flakey_c *fc = ti->private;
+
+	bio->bi_bdev = fc->dev->bdev;
+	if (bio_sectors(bio))
+		bio->bi_sector = flakey_map_sector(ti, bio->bi_sector);
+}
+
+static int flakey_map(struct dm_target *ti, struct bio *bio,
+		      union map_info *map_context)
+{
+	struct flakey_c *fc = ti->private;
+	unsigned elapsed;
+
+	/* Are we alive ? */
+	elapsed = (jiffies - fc->start_time) / HZ;
+	if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval)
+		return -EIO;
+
+	flakey_map_bio(ti, bio);
+
+	return DM_MAPIO_REMAPPED;
+}
+
+static int flakey_status(struct dm_target *ti, status_type_t type,
+			 char *result, unsigned int maxlen)
+{
+	struct flakey_c *fc = ti->private;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		result[0] = '\0';
+		break;
+
+	case STATUSTYPE_TABLE:
+		snprintf(result, maxlen, "%s %llu %u %u", fc->dev->name,
+			 (unsigned long long)fc->start, fc->up_interval,
+			 fc->down_interval);
+		break;
+	}
+	return 0;
+}
+
+static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
+{
+	struct flakey_c *fc = ti->private;
+
+	return __blkdev_driver_ioctl(fc->dev->bdev, fc->dev->mode, cmd, arg);
+}
+
+static int flakey_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
+			struct bio_vec *biovec, int max_size)
+{
+	struct flakey_c *fc = ti->private;
+	struct request_queue *q = bdev_get_queue(fc->dev->bdev);
+
+	if (!q->merge_bvec_fn)
+		return max_size;
+
+	bvm->bi_bdev = fc->dev->bdev;
+	bvm->bi_sector = flakey_map_sector(ti, bvm->bi_sector);
+
+	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
+static int flakey_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
+{
+	struct flakey_c *fc = ti->private;
+
+	return fn(ti, fc->dev, fc->start, ti->len, data);
+}
+
+static struct target_type flakey_target = {
+	.name   = "flakey",
+	.version = {1, 1, 0},
+	.module = THIS_MODULE,
+	.ctr    = flakey_ctr,
+	.dtr    = flakey_dtr,
+	.map    = flakey_map,
+	.status = flakey_status,
+	.ioctl	= flakey_ioctl,
+	.merge	= flakey_merge,
+	.iterate_devices = flakey_iterate_devices,
+};
+
+static int __init dm_flakey_init(void)
+{
+	int r = dm_register_target(&flakey_target);
+
+	if (r < 0)
+		DMERR("register failed %d", r);
+
+	return r;
+}
+
+static void __exit dm_flakey_exit(void)
+{
+	dm_unregister_target(&flakey_target);
+}
+
+/* Module hooks */
+module_init(dm_flakey_init);
+module_exit(dm_flakey_exit);
+
+MODULE_DESCRIPTION(DM_NAME " flakey target");
+MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");