dm: delay target

New device-mapper target that can delay I/O (for testing).  Reads can be
separated from writes, redirected to different underlying devices and delayed
by differing amounts of time.

Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com>
Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 393 insertions, 0 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 4540ade6b6b5..7df934d69134 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -262,6 +262,15 @@ config DM_MULTIPATH_EMC
         ---help---
           Multipath support for EMC CX/AX series hardware.
 
+config DM_DELAY
+        tristate "I/O delaying target (EXPERIMENTAL)"
+        depends on BLK_DEV_DM && EXPERIMENTAL
+        ---help---
+        A target that delays reads and/or writes and can send
+        them to different devices.  Useful for testing.
+
+        If unsure, say N.
+
 endmenu
 
 endif
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 34957a68d921..38754084eac7 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -31,6 +31,7 @@ obj-$(CONFIG_MD_FAULTY)		+= faulty.o
 obj-$(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_MULTIPATH)      += dm-multipath.o dm-round-robin.o
 obj-$(CONFIG_DM_MULTIPATH_EMC)  += dm-emc.o
 obj-$(CONFIG_DM_SNAPSHOT)       += dm-snapshot.o
diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
new file mode 100644
index 000000000000..52c7cf9e5803
--- /dev/null
+++ b/drivers/md/dm-delay.c
@@ -0,0 +1,383 @@
+/*
+ * Copyright (C) 2005-2007 Red Hat GmbH
+ *
+ * A target that delays reads and/or writes and can send
+ * them to different devices.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+
+#include "dm.h"
+#include "dm-bio-list.h"
+
+#define DM_MSG_PREFIX "delay"
+
+struct delay_c {
+        struct timer_list delay_timer;
+        struct semaphore timer_lock;
+        struct work_struct flush_expired_bios;
+        struct list_head delayed_bios;
+        atomic_t may_delay;
+        mempool_t *delayed_pool;
+
+        struct dm_dev *dev_read;
+        sector_t start_read;
+        unsigned read_delay;
+        unsigned reads;
+
+        struct dm_dev *dev_write;
+        sector_t start_write;
+        unsigned write_delay;
+        unsigned writes;
+};
+
+struct delay_info {
+        struct delay_c *context;
+        struct list_head list;
+        struct bio *bio;
+        unsigned long expires;
+};
+
+static DEFINE_MUTEX(delayed_bios_lock);
+
+static struct workqueue_struct *kdelayd_wq;
+static struct kmem_cache *delayed_cache;
+
+static void handle_delayed_timer(unsigned long data)
+{
+        struct delay_c *dc = (struct delay_c *)data;
+
+        queue_work(kdelayd_wq, &dc->flush_expired_bios);
+}
+
+static void queue_timeout(struct delay_c *dc, unsigned long expires)
+{
+        down(&dc->timer_lock);
+
+        if (!timer_pending(&dc->delay_timer) || expires < dc->delay_timer.expires)
+                mod_timer(&dc->delay_timer, expires);
+
+        up(&dc->timer_lock);
+}
+
+static void flush_bios(struct bio *bio)
+{
+        struct bio *n;
+
+        while (bio) {
+                n = bio->bi_next;
+                bio->bi_next = NULL;
+                generic_make_request(bio);
+                bio = n;
+        }
+}
+
+static struct bio *flush_delayed_bios(struct delay_c *dc, int flush_all)
+{
+        struct delay_info *delayed, *next;
+        unsigned long next_expires = 0;
+        int start_timer = 0;
+        BIO_LIST(flush_bios);
+
+        mutex_lock(&delayed_bios_lock);
+        list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) {
+                if (flush_all || time_after_eq(jiffies, delayed->expires)) {
+                        list_del(&delayed->list);
+                        bio_list_add(&flush_bios, delayed->bio);
+                        if ((bio_data_dir(delayed->bio) == WRITE))
+                                delayed->context->writes--;
+                        else
+                                delayed->context->reads--;
+                        mempool_free(delayed, dc->delayed_pool);
+                        continue;
+                }
+
+                if (!start_timer) {
+                        start_timer = 1;
+                        next_expires = delayed->expires;
+                } else
+                        next_expires = min(next_expires, delayed->expires);
+        }
+
+        mutex_unlock(&delayed_bios_lock);
+
+        if (start_timer)
+                queue_timeout(dc, next_expires);
+
+        return bio_list_get(&flush_bios);
+}
+
+static void flush_expired_bios(struct work_struct *work)
+{
+        struct delay_c *dc;
+
+        dc = container_of(work, struct delay_c, flush_expired_bios);
+        flush_bios(flush_delayed_bios(dc, 0));
+}
+
+/*
+ * Mapping parameters:
+ *    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>]
+ *
+ * With separate write parameters, the first set is only used for reads.
+ * Delays are specified in milliseconds.
+ */
+static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+        struct delay_c *dc;
+        unsigned long long tmpll;
+
+        if (argc != 3 && argc != 6) {
+                ti->error = "requires exactly 3 or 6 arguments";
+                return -EINVAL;
+        }
+
+        dc = kmalloc(sizeof(*dc), GFP_KERNEL);
+        if (!dc) {
+                ti->error = "Cannot allocate context";
+                return -ENOMEM;
+        }
+
+        dc->reads = dc->writes = 0;
+
+        if (sscanf(argv[1], "%llu", &tmpll) != 1) {
+                ti->error = "Invalid device sector";
+                goto bad;
+        }
+        dc->start_read = tmpll;
+
+        if (sscanf(argv[2], "%u", &dc->read_delay) != 1) {
+                ti->error = "Invalid delay";
+                goto bad;
+        }
+
+        if (dm_get_device(ti, argv[0], dc->start_read, ti->len,
+                          dm_table_get_mode(ti->table), &dc->dev_read)) {
+                ti->error = "Device lookup failed";
+                goto bad;
+        }
+
+        if (argc == 3) {
+                dc->dev_write = NULL;
+                goto out;
+        }
+
+        if (sscanf(argv[4], "%llu", &tmpll) != 1) {
+                ti->error = "Invalid write device sector";
+                goto bad;
+        }
+        dc->start_write = tmpll;
+
+        if (sscanf(argv[5], "%u", &dc->write_delay) != 1) {
+                ti->error = "Invalid write delay";
+                goto bad;
+        }
+
+        if (dm_get_device(ti, argv[3], dc->start_write, ti->len,
+                          dm_table_get_mode(ti->table), &dc->dev_write)) {
+                ti->error = "Write device lookup failed";
+                dm_put_device(ti, dc->dev_read);
+                goto bad;
+        }
+
+out:
+        dc->delayed_pool = mempool_create_slab_pool(128, delayed_cache);
+        if (!dc->delayed_pool) {
+                DMERR("Couldn't create delayed bio pool.");
+                goto bad;
+        }
+
+        init_timer(&dc->delay_timer);
+        dc->delay_timer.function = handle_delayed_timer;
+        dc->delay_timer.data = (unsigned long)dc;
+
+        INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
+        INIT_LIST_HEAD(&dc->delayed_bios);
+        init_MUTEX(&dc->timer_lock);
+        atomic_set(&dc->may_delay, 1);
+
+        ti->private = dc;
+        return 0;
+
+bad:
+        kfree(dc);
+        return -EINVAL;
+}
+
+static void delay_dtr(struct dm_target *ti)
+{
+        struct delay_c *dc = ti->private;
+
+        flush_workqueue(kdelayd_wq);
+
+        dm_put_device(ti, dc->dev_read);
+
+        if (dc->dev_write)
+                dm_put_device(ti, dc->dev_write);
+
+        mempool_destroy(dc->delayed_pool);
+        kfree(dc);
+}
+
+static int delay_bio(struct delay_c *dc, int delay, struct bio *bio)
+{
+        struct delay_info *delayed;
+        unsigned long expires = 0;
+
+        if (!delay || !atomic_read(&dc->may_delay))
+                return 1;
+
+        delayed = mempool_alloc(dc->delayed_pool, GFP_NOIO);
+
+        delayed->context = dc;
+        delayed->bio = bio;
+        delayed->expires = expires = jiffies + (delay * HZ / 1000);
+
+        mutex_lock(&delayed_bios_lock);
+
+        if (bio_data_dir(bio) == WRITE)
+                dc->writes++;
+        else
+                dc->reads++;
+
+        list_add_tail(&delayed->list, &dc->delayed_bios);
+
+        mutex_unlock(&delayed_bios_lock);
+
+        queue_timeout(dc, expires);
+
+        return 0;
+}
+
+static void delay_presuspend(struct dm_target *ti)
+{
+        struct delay_c *dc = ti->private;
+
+        atomic_set(&dc->may_delay, 0);
+        del_timer_sync(&dc->delay_timer);
+        flush_bios(flush_delayed_bios(dc, 1));
+}
+
+static void delay_resume(struct dm_target *ti)
+{
+        struct delay_c *dc = ti->private;
+
+        atomic_set(&dc->may_delay, 1);
+}
+
+static int delay_map(struct dm_target *ti, struct bio *bio,
+                     union map_info *map_context)
+{
+        struct delay_c *dc = ti->private;
+
+        if ((bio_data_dir(bio) == WRITE) && (dc->dev_write)) {
+                bio->bi_bdev = dc->dev_write->bdev;
+                bio->bi_sector = dc->start_write +
+                                 (bio->bi_sector - ti->begin);
+
+                return delay_bio(dc, dc->write_delay, bio);
+        }
+
+        bio->bi_bdev = dc->dev_read->bdev;
+        bio->bi_sector = dc->start_read +
+                         (bio->bi_sector - ti->begin);
+
+        return delay_bio(dc, dc->read_delay, bio);
+}
+
+static int delay_status(struct dm_target *ti, status_type_t type,
+                        char *result, unsigned maxlen)
+{
+        struct delay_c *dc = ti->private;
+        int sz = 0;
+
+        switch (type) {
+        case STATUSTYPE_INFO:
+                DMEMIT("%u %u", dc->reads, dc->writes);
+                break;
+
+        case STATUSTYPE_TABLE:
+                DMEMIT("%s %llu %u", dc->dev_read->name,
+                       (unsigned long long) dc->start_read,
+                       dc->read_delay);
+                if (dc->dev_write)
+                        DMEMIT("%s %llu %u", dc->dev_write->name,
+                               (unsigned long long) dc->start_write,
+                               dc->write_delay);
+                break;
+        }
+
+        return 0;
+}
+
+static struct target_type delay_target = {
+        .name        = "delay",
+        .version     = {1, 0, 2},
+        .module      = THIS_MODULE,
+        .ctr         = delay_ctr,
+        .dtr         = delay_dtr,
+        .map         = delay_map,
+        .presuspend  = delay_presuspend,
+        .resume      = delay_resume,
+        .status      = delay_status,
+};
+
+static int __init dm_delay_init(void)
+{
+        int r = -ENOMEM;
+
+        kdelayd_wq = create_workqueue("kdelayd");
+        if (!kdelayd_wq) {
+                DMERR("Couldn't start kdelayd");
+                goto bad_queue;
+        }
+
+        delayed_cache = kmem_cache_create("dm-delay",
+                                          sizeof(struct delay_info),
+                                          __alignof__(struct delay_info),
+                                          0, NULL, NULL);
+        if (!delayed_cache) {
+                DMERR("Couldn't create delayed bio cache.");
+                goto bad_memcache;
+        }
+
+        r = dm_register_target(&delay_target);
+        if (r < 0) {
+                DMERR("register failed %d", r);
+                goto bad_register;
+        }
+
+        return 0;
+
+bad_register:
+        kmem_cache_destroy(delayed_cache);
+bad_memcache:
+        destroy_workqueue(kdelayd_wq);
+bad_queue:
+        return r;
+}
+
+static void __exit dm_delay_exit(void)
+{
+        int r = dm_unregister_target(&delay_target);
+
+        if (r < 0)
+                DMERR("unregister failed %d", r);
+
+        kmem_cache_destroy(delayed_cache);
+        destroy_workqueue(kdelayd_wq);
+}
+
+/* Module hooks */
+module_init(dm_delay_init);
+module_exit(dm_delay_exit);
+
+MODULE_DESCRIPTION(DM_NAME " delay target");
+MODULE_AUTHOR("Heinz Mauelshagen <mauelshagen@redhat.com>");
+MODULE_LICENSE("GPL");