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>

3 files changed, 219 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 98d9ec85e0eb..8420129fc5ee 100644
--- a/drivers/md/Kconfig
+++ b/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
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index d0138606c2e8..448838b1f92a 100644
--- a/drivers/md/Makefile
+++ b/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
diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
new file mode 100644
index 000000000000..ea790623c30b
--- /dev/null
+++ b/drivers/md/dm-flakey.c
@@ -0,0 +1,212 @@
+/*
+ * 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");