9 files changed, 1448 insertions, 1 deletions

diff --git a/Documentation/device-mapper/dm-log.txt b/Documentation/device-mapper/dm-log.txt
new file mode 100644
index 000000000000..994dd75475a6
--- /dev/null
+++ b/Documentation/device-mapper/dm-log.txt
@@ -0,0 +1,54 @@
+Device-Mapper Logging
+=====================
+The device-mapper logging code is used by some of the device-mapper
+RAID targets to track regions of the disk that are not consistent.
+A region (or portion of the address space) of the disk may be
+inconsistent because a RAID stripe is currently being operated on or
+a machine died while the region was being altered.  In the case of
+mirrors, a region would be considered dirty/inconsistent while you
+are writing to it because the writes need to be replicated for all
+the legs of the mirror and may not reach the legs at the same time.
+Once all writes are complete, the region is considered clean again.
+
+There is a generic logging interface that the device-mapper RAID
+implementations use to perform logging operations (see
+dm_dirty_log_type in include/linux/dm-dirty-log.h).  Various different
+logging implementations are available and provide different
+capabilities.  The list includes:
+
+Type            Files
+====            =====
+disk            drivers/md/dm-log.c
+core            drivers/md/dm-log.c
+userspace       drivers/md/dm-log-userspace* include/linux/dm-log-userspace.h
+
+The "disk" log type
+-------------------
+This log implementation commits the log state to disk.  This way, the
+logging state survives reboots/crashes.
+
+The "core" log type
+-------------------
+This log implementation keeps the log state in memory.  The log state
+will not survive a reboot or crash, but there may be a small boost in
+performance.  This method can also be used if no storage device is
+available for storing log state.
+
+The "userspace" log type
+------------------------
+This log type simply provides a way to export the log API to userspace,
+so log implementations can be done there.  This is done by forwarding most
+logging requests to userspace, where a daemon receives and processes the
+request.
+
+The structure used for communication between kernel and userspace are
+located in include/linux/dm-log-userspace.h.  Due to the frequency,
+diversity, and 2-way communication nature of the exchanges between
+kernel and userspace, 'connector' is used as the interface for
+communication.
+
+There are currently two userspace log implementations that leverage this
+framework - "clustered_disk" and "clustered_core".  These implementations
+provide a cluster-coherent log for shared-storage.  Device-mapper mirroring
+can be used in a shared-storage environment when the cluster log implementations
+are employed.
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 09f93fa68912..020f9573fd82 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -231,6 +231,17 @@ config DM_MIRROR
          Allow volume managers to mirror logical volumes, also
          needed for live data migration tools such as 'pvmove'.
 
+config DM_LOG_USERSPACE
+        tristate "Mirror userspace logging (EXPERIMENTAL)"
+        depends on DM_MIRROR && EXPERIMENTAL && NET
+        select CONNECTOR
+        ---help---
+          The userspace logging module provides a mechanism for
+          relaying the dm-dirty-log API to userspace.  Log designs
+          which are more suited to userspace implementation (e.g.
+          shared storage logs) or experimental logs can be implemented
+          by leveraging this framework.
+
 config DM_ZERO
         tristate "Zero target"
         depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index dade52f60733..1dc4185bd781 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -8,6 +8,8 @@ dm-multipath-y	+= dm-path-selector.o dm-mpath.o
 dm-snapshot-y   += dm-snap.o dm-exception-store.o dm-snap-transient.o \
                     dm-snap-persistent.o
 dm-mirror-y     += dm-raid1.o
+dm-log-userspace-y \
+                += dm-log-userspace-base.o dm-log-userspace-transfer.o
 md-mod-y        += md.o bitmap.o
 raid456-y       += raid5.o
 raid6_pq-y      += raid6algos.o raid6recov.o raid6tables.o \
@@ -40,6 +42,7 @@ obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o
 obj-$(CONFIG_DM_MULTIPATH_ST)   += dm-service-time.o
 obj-$(CONFIG_DM_SNAPSHOT)       += dm-snapshot.o
 obj-$(CONFIG_DM_MIRROR)         += dm-mirror.o dm-log.o dm-region-hash.o
+obj-$(CONFIG_DM_LOG_USERSPACE)  += dm-log-userspace.o
 obj-$(CONFIG_DM_ZERO)           += dm-zero.o
 
 quiet_cmd_unroll = UNROLL  $@
diff --git a/drivers/md/dm-log-userspace-base.c b/drivers/md/dm-log-userspace-base.c
new file mode 100644
index 000000000000..e69b96560997
--- /dev/null
+++ b/drivers/md/dm-log-userspace-base.c
@@ -0,0 +1,696 @@
+/*
+ * Copyright (C) 2006-2009 Red Hat, Inc.
+ *
+ * This file is released under the LGPL.
+ */
+
+#include <linux/bio.h>
+#include <linux/dm-dirty-log.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-log-userspace.h>
+
+#include "dm-log-userspace-transfer.h"
+
+struct flush_entry {
+        int type;
+        region_t region;
+        struct list_head list;
+};
+
+struct log_c {
+        struct dm_target *ti;
+        uint32_t region_size;
+        region_t region_count;
+        char uuid[DM_UUID_LEN];
+
+        char *usr_argv_str;
+        uint32_t usr_argc;
+
+        /*
+         * in_sync_hint gets set when doing is_remote_recovering.  It
+         * represents the first region that needs recovery.  IOW, the
+         * first zero bit of sync_bits.  This can be useful for to limit
+         * traffic for calls like is_remote_recovering and get_resync_work,
+         * but be take care in its use for anything else.
+         */
+        uint64_t in_sync_hint;
+
+        spinlock_t flush_lock;
+        struct list_head flush_list;  /* only for clear and mark requests */
+};
+
+static mempool_t *flush_entry_pool;
+
+static void *flush_entry_alloc(gfp_t gfp_mask, void *pool_data)
+{
+        return kmalloc(sizeof(struct flush_entry), gfp_mask);
+}
+
+static void flush_entry_free(void *element, void *pool_data)
+{
+        kfree(element);
+}
+
+static int userspace_do_request(struct log_c *lc, const char *uuid,
+                                int request_type, char *data, size_t data_size,
+                                char *rdata, size_t *rdata_size)
+{
+        int r;
+
+        /*
+         * If the server isn't there, -ESRCH is returned,
+         * and we must keep trying until the server is
+         * restored.
+         */
+retry:
+        r = dm_consult_userspace(uuid, request_type, data,
+                                 data_size, rdata, rdata_size);
+
+        if (r != -ESRCH)
+                return r;
+
+        DMERR(" Userspace log server not found.");
+        while (1) {
+                set_current_state(TASK_INTERRUPTIBLE);
+                schedule_timeout(2*HZ);
+                DMWARN("Attempting to contact userspace log server...");
+                r = dm_consult_userspace(uuid, DM_ULOG_CTR, lc->usr_argv_str,
+                                         strlen(lc->usr_argv_str) + 1,
+                                         NULL, NULL);
+                if (!r)
+                        break;
+        }
+        DMINFO("Reconnected to userspace log server... DM_ULOG_CTR complete");
+        r = dm_consult_userspace(uuid, DM_ULOG_RESUME, NULL,
+                                 0, NULL, NULL);
+        if (!r)
+                goto retry;
+
+        DMERR("Error trying to resume userspace log: %d", r);
+
+        return -ESRCH;
+}
+
+static int build_constructor_string(struct dm_target *ti,
+                                    unsigned argc, char **argv,
+                                    char **ctr_str)
+{
+        int i, str_size;
+        char *str = NULL;
+
+        *ctr_str = NULL;
+
+        for (i = 0, str_size = 0; i < argc; i++)
+                str_size += strlen(argv[i]) + 1; /* +1 for space between args */
+
+        str_size += 20; /* Max number of chars in a printed u64 number */
+
+        str = kzalloc(str_size, GFP_KERNEL);
+        if (!str) {
+                DMWARN("Unable to allocate memory for constructor string");
+                return -ENOMEM;
+        }
+
+        for (i = 0, str_size = 0; i < argc; i++)
+                str_size += sprintf(str + str_size, "%s ", argv[i]);
+        str_size += sprintf(str + str_size, "%llu",
+                            (unsigned long long)ti->len);
+
+        *ctr_str = str;
+        return str_size;
+}
+
+/*
+ * userspace_ctr
+ *
+ * argv contains:
+ *      <UUID> <other args>
+ * Where 'other args' is the userspace implementation specific log
+ * arguments.  An example might be:
+ *      <UUID> clustered_disk <arg count> <log dev> <region_size> [[no]sync]
+ *
+ * So, this module will strip off the <UUID> for identification purposes
+ * when communicating with userspace about a log; but will pass on everything
+ * else.
+ */
+static int userspace_ctr(struct dm_dirty_log *log, struct dm_target *ti,
+                         unsigned argc, char **argv)
+{
+        int r = 0;
+        int str_size;
+        char *ctr_str = NULL;
+        struct log_c *lc = NULL;
+        uint64_t rdata;
+        size_t rdata_size = sizeof(rdata);
+
+        if (argc < 3) {
+                DMWARN("Too few arguments to userspace dirty log");
+                return -EINVAL;
+        }
+
+        lc = kmalloc(sizeof(*lc), GFP_KERNEL);
+        if (!lc) {
+                DMWARN("Unable to allocate userspace log context.");
+                return -ENOMEM;
+        }
+
+        lc->ti = ti;
+
+        if (strlen(argv[0]) > (DM_UUID_LEN - 1)) {
+                DMWARN("UUID argument too long.");
+                kfree(lc);
+                return -EINVAL;
+        }
+
+        strncpy(lc->uuid, argv[0], DM_UUID_LEN);
+        spin_lock_init(&lc->flush_lock);
+        INIT_LIST_HEAD(&lc->flush_list);
+
+        str_size = build_constructor_string(ti, argc - 1, argv + 1, &ctr_str);
+        if (str_size < 0) {
+                kfree(lc);
+                return str_size;
+        }
+
+        /* Send table string */
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_CTR,
+                                 ctr_str, str_size, NULL, NULL);
+
+        if (r == -ESRCH) {
+                DMERR("Userspace log server not found");
+                goto out;
+        }
+
+        /* Since the region size does not change, get it now */
+        rdata_size = sizeof(rdata);
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_GET_REGION_SIZE,
+                                 NULL, 0, (char *)&rdata, &rdata_size);
+
+        if (r) {
+                DMERR("Failed to get region size of dirty log");
+                goto out;
+        }
+
+        lc->region_size = (uint32_t)rdata;
+        lc->region_count = dm_sector_div_up(ti->len, lc->region_size);
+
+out:
+        if (r) {
+                kfree(lc);
+                kfree(ctr_str);
+        } else {
+                lc->usr_argv_str = ctr_str;
+                lc->usr_argc = argc;
+                log->context = lc;
+        }
+
+        return r;
+}
+
+static void userspace_dtr(struct dm_dirty_log *log)
+{
+        int r;
+        struct log_c *lc = log->context;
+
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_DTR,
+                                 NULL, 0,
+                                 NULL, NULL);
+
+        kfree(lc->usr_argv_str);
+        kfree(lc);
+
+        return;
+}
+
+static int userspace_presuspend(struct dm_dirty_log *log)
+{
+        int r;
+        struct log_c *lc = log->context;
+
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_PRESUSPEND,
+                                 NULL, 0,
+                                 NULL, NULL);
+
+        return r;
+}
+
+static int userspace_postsuspend(struct dm_dirty_log *log)
+{
+        int r;
+        struct log_c *lc = log->context;
+
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_POSTSUSPEND,
+                                 NULL, 0,
+                                 NULL, NULL);
+
+        return r;
+}
+
+static int userspace_resume(struct dm_dirty_log *log)
+{
+        int r;
+        struct log_c *lc = log->context;
+
+        lc->in_sync_hint = 0;
+        r = dm_consult_userspace(lc->uuid, DM_ULOG_RESUME,
+                                 NULL, 0,
+                                 NULL, NULL);
+
+        return r;
+}
+
+static uint32_t userspace_get_region_size(struct dm_dirty_log *log)
+{
+        struct log_c *lc = log->context;
+
+        return lc->region_size;
+}
+
+/*
+ * userspace_is_clean
+ *
+ * Check whether a region is clean.  If there is any sort of
+ * failure when consulting the server, we return not clean.
+ *
+ * Returns: 1 if clean, 0 otherwise
+ */
+static int userspace_is_clean(struct dm_dirty_log *log, region_t region)
+{
+        int r;
+        uint64_t region64 = (uint64_t)region;
+        int64_t is_clean;
+        size_t rdata_size;
+        struct log_c *lc = log->context;
+
+        rdata_size = sizeof(is_clean);
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_IS_CLEAN,
+                                 (char *)&region64, sizeof(region64),
+                                 (char *)&is_clean, &rdata_size);
+
+        return (r) ? 0 : (int)is_clean;
+}
+
+/*
+ * userspace_in_sync
+ *
+ * Check if the region is in-sync.  If there is any sort
+ * of failure when consulting the server, we assume that
+ * the region is not in sync.
+ *
+ * If 'can_block' is set, return immediately
+ *
+ * Returns: 1 if in-sync, 0 if not-in-sync, -EWOULDBLOCK
+ */
+static int userspace_in_sync(struct dm_dirty_log *log, region_t region,
+                             int can_block)
+{
+        int r;
+        uint64_t region64 = region;
+        int64_t in_sync;
+        size_t rdata_size;
+        struct log_c *lc = log->context;
+
+        /*
+         * We can never respond directly - even if in_sync_hint is
+         * set.  This is because another machine could see a device
+         * failure and mark the region out-of-sync.  If we don't go
+         * to userspace to ask, we might think the region is in-sync
+         * and allow a read to pick up data that is stale.  (This is
+         * very unlikely if a device actually fails; but it is very
+         * likely if a connection to one device from one machine fails.)
+         *
+         * There still might be a problem if the mirror caches the region
+         * state as in-sync... but then this call would not be made.  So,
+         * that is a mirror problem.
+         */
+        if (!can_block)
+                return -EWOULDBLOCK;
+
+        rdata_size = sizeof(in_sync);
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_IN_SYNC,
+                                 (char *)&region64, sizeof(region64),
+                                 (char *)&in_sync, &rdata_size);
+        return (r) ? 0 : (int)in_sync;
+}
+
+/*
+ * userspace_flush
+ *
+ * This function is ok to block.
+ * The flush happens in two stages.  First, it sends all
+ * clear/mark requests that are on the list.  Then it
+ * tells the server to commit them.  This gives the
+ * server a chance to optimise the commit, instead of
+ * doing it for every request.
+ *
+ * Additionally, we could implement another thread that
+ * sends the requests up to the server - reducing the
+ * load on flush.  Then the flush would have less in
+ * the list and be responsible for the finishing commit.
+ *
+ * Returns: 0 on success, < 0 on failure
+ */
+static int userspace_flush(struct dm_dirty_log *log)
+{
+        int r = 0;
+        unsigned long flags;
+        struct log_c *lc = log->context;
+        LIST_HEAD(flush_list);
+        struct flush_entry *fe, *tmp_fe;
+
+        spin_lock_irqsave(&lc->flush_lock, flags);
+        list_splice_init(&lc->flush_list, &flush_list);
+        spin_unlock_irqrestore(&lc->flush_lock, flags);
+
+        if (list_empty(&flush_list))
+                return 0;
+
+        /*
+         * FIXME: Count up requests, group request types,
+         * allocate memory to stick all requests in and
+         * send to server in one go.  Failing the allocation,
+         * do it one by one.
+         */
+
+        list_for_each_entry(fe, &flush_list, list) {
+                r = userspace_do_request(lc, lc->uuid, fe->type,
+                                         (char *)&fe->region,
+                                         sizeof(fe->region),
+                                         NULL, NULL);
+                if (r)
+                        goto fail;
+        }
+
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_FLUSH,
+                                 NULL, 0, NULL, NULL);
+
+fail:
+        /*
+         * We can safely remove these entries, even if failure.
+         * Calling code will receive an error and will know that
+         * the log facility has failed.
+         */
+        list_for_each_entry_safe(fe, tmp_fe, &flush_list, list) {
+                list_del(&fe->list);
+                mempool_free(fe, flush_entry_pool);
+        }
+
+        if (r)
+                dm_table_event(lc->ti->table);
+
+        return r;
+}
+
+/*
+ * userspace_mark_region
+ *
+ * This function should avoid blocking unless absolutely required.
+ * (Memory allocation is valid for blocking.)
+ */
+static void userspace_mark_region(struct dm_dirty_log *log, region_t region)
+{
+        unsigned long flags;
+        struct log_c *lc = log->context;
+        struct flush_entry *fe;
+
+        /* Wait for an allocation, but _never_ fail */
+        fe = mempool_alloc(flush_entry_pool, GFP_NOIO);
+        BUG_ON(!fe);
+
+        spin_lock_irqsave(&lc->flush_lock, flags);
+        fe->type = DM_ULOG_MARK_REGION;
+        fe->region = region;
+        list_add(&fe->list, &lc->flush_list);
+        spin_unlock_irqrestore(&lc->flush_lock, flags);
+
+        return;
+}
+
+/*
+ * userspace_clear_region
+ *
+ * This function must not block.
+ * So, the alloc can't block.  In the worst case, it is ok to
+ * fail.  It would simply mean we can't clear the region.
+ * Does nothing to current sync context, but does mean
+ * the region will be re-sync'ed on a reload of the mirror
+ * even though it is in-sync.
+ */
+static void userspace_clear_region(struct dm_dirty_log *log, region_t region)
+{
+        unsigned long flags;
+        struct log_c *lc = log->context;
+        struct flush_entry *fe;
+
+        /*
+         * If we fail to allocate, we skip the clearing of
+         * the region.  This doesn't hurt us in any way, except
+         * to cause the region to be resync'ed when the
+         * device is activated next time.
+         */
+        fe = mempool_alloc(flush_entry_pool, GFP_ATOMIC);
+        if (!fe) {
+                DMERR("Failed to allocate memory to clear region.");
+                return;
+        }
+
+        spin_lock_irqsave(&lc->flush_lock, flags);
+        fe->type = DM_ULOG_CLEAR_REGION;
+        fe->region = region;
+        list_add(&fe->list, &lc->flush_list);
+        spin_unlock_irqrestore(&lc->flush_lock, flags);
+
+        return;
+}
+
+/*
+ * userspace_get_resync_work
+ *
+ * Get a region that needs recovery.  It is valid to return
+ * an error for this function.
+ *
+ * Returns: 1 if region filled, 0 if no work, <0 on error
+ */
+static int userspace_get_resync_work(struct dm_dirty_log *log, region_t *region)
+{
+        int r;
+        size_t rdata_size;
+        struct log_c *lc = log->context;
+        struct {
+                int64_t i; /* 64-bit for mix arch compatibility */
+                region_t r;
+        } pkg;
+
+        if (lc->in_sync_hint >= lc->region_count)
+                return 0;
+
+        rdata_size = sizeof(pkg);
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_GET_RESYNC_WORK,
+                                 NULL, 0,
+                                 (char *)&pkg, &rdata_size);
+
+        *region = pkg.r;
+        return (r) ? r : (int)pkg.i;
+}
+
+/*
+ * userspace_set_region_sync
+ *
+ * Set the sync status of a given region.  This function
+ * must not fail.
+ */
+static void userspace_set_region_sync(struct dm_dirty_log *log,
+                                      region_t region, int in_sync)
+{
+        int r;
+        struct log_c *lc = log->context;
+        struct {
+                region_t r;
+                int64_t i;
+        } pkg;
+
+        pkg.r = region;
+        pkg.i = (int64_t)in_sync;
+
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_SET_REGION_SYNC,
+                                 (char *)&pkg, sizeof(pkg),
+                                 NULL, NULL);
+
+        /*
+         * It would be nice to be able to report failures.
+         * However, it is easy emough to detect and resolve.
+         */
+        return;
+}
+
+/*
+ * userspace_get_sync_count
+ *
+ * If there is any sort of failure when consulting the server,
+ * we assume that the sync count is zero.
+ *
+ * Returns: sync count on success, 0 on failure
+ */
+static region_t userspace_get_sync_count(struct dm_dirty_log *log)
+{
+        int r;
+        size_t rdata_size;
+        uint64_t sync_count;
+        struct log_c *lc = log->context;
+
+        rdata_size = sizeof(sync_count);
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_GET_SYNC_COUNT,
+                                 NULL, 0,
+                                 (char *)&sync_count, &rdata_size);
+
+        if (r)
+                return 0;
+
+        if (sync_count >= lc->region_count)
+                lc->in_sync_hint = lc->region_count;
+
+        return (region_t)sync_count;
+}
+
+/*
+ * userspace_status
+ *
+ * Returns: amount of space consumed
+ */
+static int userspace_status(struct dm_dirty_log *log, status_type_t status_type,
+                            char *result, unsigned maxlen)
+{
+        int r = 0;
+        size_t sz = (size_t)maxlen;
+        struct log_c *lc = log->context;
+
+        switch (status_type) {
+        case STATUSTYPE_INFO:
+                r = userspace_do_request(lc, lc->uuid, DM_ULOG_STATUS_INFO,
+                                         NULL, 0,
+                                         result, &sz);
+
+                if (r) {
+                        sz = 0;
+                        DMEMIT("%s 1 COM_FAILURE", log->type->name);
+                }
+                break;
+        case STATUSTYPE_TABLE:
+                sz = 0;
+                DMEMIT("%s %u %s %s", log->type->name, lc->usr_argc + 1,
+                       lc->uuid, lc->usr_argv_str);
+                break;
+        }
+        return (r) ? 0 : (int)sz;
+}
+
+/*
+ * userspace_is_remote_recovering
+ *
+ * Returns: 1 if region recovering, 0 otherwise
+ */
+static int userspace_is_remote_recovering(struct dm_dirty_log *log,
+                                          region_t region)
+{
+        int r;
+        uint64_t region64 = region;
+        struct log_c *lc = log->context;
+        static unsigned long long limit;
+        struct {
+                int64_t is_recovering;
+                uint64_t in_sync_hint;
+        } pkg;
+        size_t rdata_size = sizeof(pkg);
+
+        /*
+         * Once the mirror has been reported to be in-sync,
+         * it will never again ask for recovery work.  So,
+         * we can safely say there is not a remote machine
+         * recovering if the device is in-sync.  (in_sync_hint
+         * must be reset at resume time.)
+         */
+        if (region < lc->in_sync_hint)
+                return 0;
+        else if (jiffies < limit)
+                return 1;
+
+        limit = jiffies + (HZ / 4);
+        r = userspace_do_request(lc, lc->uuid, DM_ULOG_IS_REMOTE_RECOVERING,
+                                 (char *)&region64, sizeof(region64),
+                                 (char *)&pkg, &rdata_size);
+        if (r)
+                return 1;
+
+        lc->in_sync_hint = pkg.in_sync_hint;
+
+        return (int)pkg.is_recovering;
+}
+
+static struct dm_dirty_log_type _userspace_type = {
+        .name = "userspace",
+        .module = THIS_MODULE,
+        .ctr = userspace_ctr,
+        .dtr = userspace_dtr,
+        .presuspend = userspace_presuspend,
+        .postsuspend = userspace_postsuspend,
+        .resume = userspace_resume,
+        .get_region_size = userspace_get_region_size,
+        .is_clean = userspace_is_clean,
+        .in_sync = userspace_in_sync,
+        .flush = userspace_flush,
+        .mark_region = userspace_mark_region,
+        .clear_region = userspace_clear_region,
+        .get_resync_work = userspace_get_resync_work,
+        .set_region_sync = userspace_set_region_sync,
+        .get_sync_count = userspace_get_sync_count,
+        .status = userspace_status,
+        .is_remote_recovering = userspace_is_remote_recovering,
+};
+
+static int __init userspace_dirty_log_init(void)
+{
+        int r = 0;
+
+        flush_entry_pool = mempool_create(100, flush_entry_alloc,
+                                          flush_entry_free, NULL);
+
+        if (!flush_entry_pool) {
+                DMWARN("Unable to create flush_entry_pool:  No memory.");
+                return -ENOMEM;
+        }
+
+        r = dm_ulog_tfr_init();
+        if (r) {
+                DMWARN("Unable to initialize userspace log communications");
+                mempool_destroy(flush_entry_pool);
+                return r;
+        }
+
+        r = dm_dirty_log_type_register(&_userspace_type);
+        if (r) {
+                DMWARN("Couldn't register userspace dirty log type");
+                dm_ulog_tfr_exit();
+                mempool_destroy(flush_entry_pool);
+                return r;
+        }
+
+        DMINFO("version 1.0.0 loaded");
+        return 0;
+}
+
+static void __exit userspace_dirty_log_exit(void)
+{
+        dm_dirty_log_type_unregister(&_userspace_type);
+        dm_ulog_tfr_exit();
+        mempool_destroy(flush_entry_pool);
+
+        DMINFO("version 1.0.0 unloaded");
+        return;
+}
+
+module_init(userspace_dirty_log_init);
+module_exit(userspace_dirty_log_exit);
+
+MODULE_DESCRIPTION(DM_NAME " userspace dirty log link");
+MODULE_AUTHOR("Jonathan Brassow <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");
diff --git a/drivers/md/dm-log-userspace-transfer.c b/drivers/md/dm-log-userspace-transfer.c
new file mode 100644
index 000000000000..0ca1ee768a1f
--- /dev/null
+++ b/drivers/md/dm-log-userspace-transfer.c
@@ -0,0 +1,276 @@
+/*
+ * Copyright (C) 2006-2009 Red Hat, Inc.
+ *
+ * This file is released under the LGPL.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <net/sock.h>
+#include <linux/workqueue.h>
+#include <linux/connector.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-log-userspace.h>
+
+#include "dm-log-userspace-transfer.h"
+
+static uint32_t dm_ulog_seq;
+
+/*
+ * Netlink/Connector is an unreliable protocol.  How long should
+ * we wait for a response before assuming it was lost and retrying?
+ * (If we do receive a response after this time, it will be discarded
+ * and the response to the resent request will be waited for.
+ */
+#define DM_ULOG_RETRY_TIMEOUT (15 * HZ)
+
+/*
+ * Pre-allocated space for speed
+ */
+#define DM_ULOG_PREALLOCED_SIZE 512
+static struct cn_msg *prealloced_cn_msg;
+static struct dm_ulog_request *prealloced_ulog_tfr;
+
+static struct cb_id ulog_cn_id = {
+        .idx = CN_IDX_DM,
+        .val = CN_VAL_DM_USERSPACE_LOG
+};
+
+static DEFINE_MUTEX(dm_ulog_lock);
+
+struct receiving_pkg {
+        struct list_head list;
+        struct completion complete;
+
+        uint32_t seq;
+
+        int error;
+        size_t *data_size;
+        char *data;
+};
+
+static DEFINE_SPINLOCK(receiving_list_lock);
+static struct list_head receiving_list;
+
+static int dm_ulog_sendto_server(struct dm_ulog_request *tfr)
+{
+        int r;
+        struct cn_msg *msg = prealloced_cn_msg;
+
+        memset(msg, 0, sizeof(struct cn_msg));
+
+        msg->id.idx = ulog_cn_id.idx;
+        msg->id.val = ulog_cn_id.val;
+        msg->ack = 0;
+        msg->seq = tfr->seq;
+        msg->len = sizeof(struct dm_ulog_request) + tfr->data_size;
+
+        r = cn_netlink_send(msg, 0, gfp_any());
+
+        return r;
+}
+
+/*
+ * Parameters for this function can be either msg or tfr, but not
+ * both.  This function fills in the reply for a waiting request.
+ * If just msg is given, then the reply is simply an ACK from userspace
+ * that the request was received.
+ *
+ * Returns: 0 on success, -ENOENT on failure
+ */
+static int fill_pkg(struct cn_msg *msg, struct dm_ulog_request *tfr)
+{
+        uint32_t rtn_seq = (msg) ? msg->seq : (tfr) ? tfr->seq : 0;
+        struct receiving_pkg *pkg;
+
+        /*
+         * The 'receiving_pkg' entries in this list are statically
+         * allocated on the stack in 'dm_consult_userspace'.
+         * Each process that is waiting for a reply from the user
+         * space server will have an entry in this list.
+         *
+         * We are safe to do it this way because the stack space
+         * is unique to each process, but still addressable by
+         * other processes.
+         */
+        list_for_each_entry(pkg, &receiving_list, list) {
+                if (rtn_seq != pkg->seq)
+                        continue;
+
+                if (msg) {
+                        pkg->error = -msg->ack;
+                        /*
+                         * If we are trying again, we will need to know our
+                         * storage capacity.  Otherwise, along with the
+                         * error code, we make explicit that we have no data.
+                         */
+                        if (pkg->error != -EAGAIN)
+                                *(pkg->data_size) = 0;
+                } else if (tfr->data_size > *(pkg->data_size)) {
+                        DMERR("Insufficient space to receive package [%u] "
+                              "(%u vs %lu)", tfr->request_type,
+                              tfr->data_size, *(pkg->data_size));
+
+                        *(pkg->data_size) = 0;
+                        pkg->error = -ENOSPC;
+                } else {
+                        pkg->error = tfr->error;
+                        memcpy(pkg->data, tfr->data, tfr->data_size);
+                        *(pkg->data_size) = tfr->data_size;
+                }
+                complete(&pkg->complete);
+                return 0;
+        }
+
+        return -ENOENT;
+}
+
+/*
+ * This is the connector callback that delivers data
+ * that was sent from userspace.
+ */
+static void cn_ulog_callback(void *data)
+{
+        struct cn_msg *msg = (struct cn_msg *)data;
+        struct dm_ulog_request *tfr = (struct dm_ulog_request *)(msg + 1);
+
+        spin_lock(&receiving_list_lock);
+        if (msg->len == 0)
+                fill_pkg(msg, NULL);
+        else if (msg->len < sizeof(*tfr))
+                DMERR("Incomplete message received (expected %u, got %u): [%u]",
+                      (unsigned)sizeof(*tfr), msg->len, msg->seq);
+        else
+                fill_pkg(NULL, tfr);
+        spin_unlock(&receiving_list_lock);
+}
+
+/**
+ * dm_consult_userspace
+ * @uuid: log's uuid (must be DM_UUID_LEN in size)
+ * @request_type:  found in include/linux/dm-log-userspace.h
+ * @data: data to tx to the server
+ * @data_size: size of data in bytes
+ * @rdata: place to put return data from server
+ * @rdata_size: value-result (amount of space given/amount of space used)
+ *
+ * rdata_size is undefined on failure.
+ *
+ * Memory used to communicate with userspace is zero'ed
+ * before populating to ensure that no unwanted bits leak
+ * from kernel space to user-space.  All userspace log communications
+ * between kernel and user space go through this function.
+ *
+ * Returns: 0 on success, -EXXX on failure
+ **/
+int dm_consult_userspace(const char *uuid, int request_type,
+                         char *data, size_t data_size,
+                         char *rdata, size_t *rdata_size)
+{
+        int r = 0;
+        size_t dummy = 0;
+        int overhead_size =
+                sizeof(struct dm_ulog_request *) + sizeof(struct cn_msg);
+        struct dm_ulog_request *tfr = prealloced_ulog_tfr;
+        struct receiving_pkg pkg;
+
+        if (data_size > (DM_ULOG_PREALLOCED_SIZE - overhead_size)) {
+                DMINFO("Size of tfr exceeds preallocated size");
+                return -EINVAL;
+        }
+
+        if (!rdata_size)
+                rdata_size = &dummy;
+resend:
+        /*
+         * We serialize the sending of requests so we can
+         * use the preallocated space.
+         */
+        mutex_lock(&dm_ulog_lock);
+
+        memset(tfr, 0, DM_ULOG_PREALLOCED_SIZE - overhead_size);
+        memcpy(tfr->uuid, uuid, DM_UUID_LEN);
+        tfr->seq = dm_ulog_seq++;
+
+        /*
+         * Must be valid request type (all other bits set to
+         * zero).  This reserves other bits for possible future
+         * use.
+         */
+        tfr->request_type = request_type & DM_ULOG_REQUEST_MASK;
+
+        tfr->data_size = data_size;
+        if (data && data_size)
+                memcpy(tfr->data, data, data_size);
+
+        memset(&pkg, 0, sizeof(pkg));
+        init_completion(&pkg.complete);
+        pkg.seq = tfr->seq;
+        pkg.data_size = rdata_size;
+        pkg.data = rdata;
+        spin_lock(&receiving_list_lock);
+        list_add(&(pkg.list), &receiving_list);
+        spin_unlock(&receiving_list_lock);
+
+        r = dm_ulog_sendto_server(tfr);
+
+        mutex_unlock(&dm_ulog_lock);
+
+        if (r) {
+                DMERR("Unable to send log request [%u] to userspace: %d",
+                      request_type, r);
+                spin_lock(&receiving_list_lock);
+                list_del_init(&(pkg.list));
+                spin_unlock(&receiving_list_lock);
+
+                goto out;
+        }
+
+        r = wait_for_completion_timeout(&(pkg.complete), DM_ULOG_RETRY_TIMEOUT);
+        spin_lock(&receiving_list_lock);
+        list_del_init(&(pkg.list));
+        spin_unlock(&receiving_list_lock);
+        if (!r) {
+                DMWARN("[%s] Request timed out: [%u/%u] - retrying",
+                       (strlen(uuid) > 8) ?
+                       (uuid + (strlen(uuid) - 8)) : (uuid),
+                       request_type, pkg.seq);
+                goto resend;
+        }
+
+        r = pkg.error;
+        if (r == -EAGAIN)
+                goto resend;
+
+out:
+        return r;
+}
+
+int dm_ulog_tfr_init(void)
+{
+        int r;
+        void *prealloced;
+
+        INIT_LIST_HEAD(&receiving_list);
+
+        prealloced = kmalloc(DM_ULOG_PREALLOCED_SIZE, GFP_KERNEL);
+        if (!prealloced)
+                return -ENOMEM;
+
+        prealloced_cn_msg = prealloced;
+        prealloced_ulog_tfr = prealloced + sizeof(struct cn_msg);
+
+        r = cn_add_callback(&ulog_cn_id, "dmlogusr", cn_ulog_callback);
+        if (r) {
+                cn_del_callback(&ulog_cn_id);
+                return r;
+        }
+
+        return 0;
+}
+
+void dm_ulog_tfr_exit(void)
+{
+        cn_del_callback(&ulog_cn_id);
+        kfree(prealloced_cn_msg);
+}
diff --git a/drivers/md/dm-log-userspace-transfer.h b/drivers/md/dm-log-userspace-transfer.h
new file mode 100644
index 000000000000..c26d8e4e2710
--- /dev/null
+++ b/drivers/md/dm-log-userspace-transfer.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (C) 2006-2009 Red Hat, Inc.
+ *
+ * This file is released under the LGPL.
+ */
+
+#ifndef __DM_LOG_USERSPACE_TRANSFER_H__
+#define __DM_LOG_USERSPACE_TRANSFER_H__
+
+#define DM_MSG_PREFIX "dm-log-userspace"
+
+int dm_ulog_tfr_init(void);
+void dm_ulog_tfr_exit(void);
+int dm_consult_userspace(const char *uuid, int request_type,
+                         char *data, size_t data_size,
+                         char *rdata, size_t *rdata_size);
+
+#endif /* __DM_LOG_USERSPACE_TRANSFER_H__ */
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 03f22076381f..334a3593cdfd 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -57,6 +57,7 @@ header-y += dlmconstants.h
 header-y += dlm_device.h
 header-y += dlm_netlink.h
 header-y += dm-ioctl.h
+header-y += dm-log-userspace.h
 header-y += dn.h
 header-y += dqblk_xfs.h
 header-y += efs_fs_sb.h
diff --git a/include/linux/connector.h b/include/linux/connector.h
index b9966e64604e..b68d27850d51 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -41,8 +41,10 @@
 #define CN_IDX_BB                       0x5     /* BlackBoard, from the TSP GPL sampling framework */
 #define CN_DST_IDX                      0x6
 #define CN_DST_VAL                      0x1
+#define CN_IDX_DM                       0x7     /* Device Mapper */
+#define CN_VAL_DM_USERSPACE_LOG         0x1
 
-#define CN_NETLINK_USERS                7
+#define CN_NETLINK_USERS                8
 
 /*
  * Maximum connector's message size.
diff --git a/include/linux/dm-log-userspace.h b/include/linux/dm-log-userspace.h
new file mode 100644
index 000000000000..642e3017b51f
--- /dev/null
+++ b/include/linux/dm-log-userspace.h
@@ -0,0 +1,386 @@
+/*
+ * Copyright (C) 2006-2009 Red Hat, Inc.
+ *
+ * This file is released under the LGPL.
+ */
+
+#ifndef __DM_LOG_USERSPACE_H__
+#define __DM_LOG_USERSPACE_H__
+
+#include <linux/dm-ioctl.h> /* For DM_UUID_LEN */
+
+/*
+ * The device-mapper userspace log module consists of a kernel component and
+ * a user-space component.  The kernel component implements the API defined
+ * in dm-dirty-log.h.  Its purpose is simply to pass the parameters and
+ * return values of those API functions between kernel and user-space.
+ *
+ * Below are defined the 'request_types' - DM_ULOG_CTR, DM_ULOG_DTR, etc.
+ * These request types represent the different functions in the device-mapper
+ * dirty log API.  Each of these is described in more detail below.
+ *
+ * The user-space program must listen for requests from the kernel (representing
+ * the various API functions) and process them.
+ *
+ * User-space begins by setting up the communication link (error checking
+ * removed for clarity):
+ *      fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
+ *      addr.nl_family = AF_NETLINK;
+ *      addr.nl_groups = CN_IDX_DM;
+ *      addr.nl_pid = 0;
+ *      r = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
+ *      opt = addr.nl_groups;
+ *      setsockopt(fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP, &opt, sizeof(opt));
+ *
+ * User-space will then wait to receive requests form the kernel, which it
+ * will process as described below.  The requests are received in the form,
+ * ((struct dm_ulog_request) + (additional data)).  Depending on the request
+ * type, there may or may not be 'additional data'.  In the descriptions below,
+ * you will see 'Payload-to-userspace' and 'Payload-to-kernel'.  The
+ * 'Payload-to-userspace' is what the kernel sends in 'additional data' as
+ * necessary parameters to complete the request.  The 'Payload-to-kernel' is
+ * the 'additional data' returned to the kernel that contains the necessary
+ * results of the request.  The 'data_size' field in the dm_ulog_request
+ * structure denotes the availability and amount of payload data.
+ */
+
+/*
+ * DM_ULOG_CTR corresponds to (found in dm-dirty-log.h):
+ * int (*ctr)(struct dm_dirty_log *log, struct dm_target *ti,
+ *            unsigned argc, char **argv);
+ *
+ * Payload-to-userspace:
+ *      A single string containing all the argv arguments separated by ' 's
+ * Payload-to-kernel:
+ *      None.  ('data_size' in the dm_ulog_request struct should be 0.)
+ *
+ * The UUID contained in the dm_ulog_request structure is the reference that
+ * will be used by all request types to a specific log.  The constructor must
+ * record this assotiation with instance created.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_CTR                    1
+
+/*
+ * DM_ULOG_DTR corresponds to (found in dm-dirty-log.h):
+ * void (*dtr)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      A single string containing all the argv arguments separated by ' 's
+ * Payload-to-kernel:
+ *      None.  ('data_size' in the dm_ulog_request struct should be 0.)
+ *
+ * The UUID contained in the dm_ulog_request structure is all that is
+ * necessary to identify the log instance being destroyed.  There is no
+ * payload data.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and clearing
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_DTR                    2
+
+/*
+ * DM_ULOG_PRESUSPEND corresponds to (found in dm-dirty-log.h):
+ * int (*presuspend)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      None.
+ *
+ * The UUID contained in the dm_ulog_request structure is all that is
+ * necessary to identify the log instance being presuspended.  There is no
+ * payload data.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_PRESUSPEND             3
+
+/*
+ * DM_ULOG_POSTSUSPEND corresponds to (found in dm-dirty-log.h):
+ * int (*postsuspend)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      None.
+ *
+ * The UUID contained in the dm_ulog_request structure is all that is
+ * necessary to identify the log instance being postsuspended.  There is no
+ * payload data.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_POSTSUSPEND            4
+
+/*
+ * DM_ULOG_RESUME corresponds to (found in dm-dirty-log.h):
+ * int (*resume)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      None.
+ *
+ * The UUID contained in the dm_ulog_request structure is all that is
+ * necessary to identify the log instance being resumed.  There is no
+ * payload data.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_RESUME                 5
+
+/*
+ * DM_ULOG_GET_REGION_SIZE corresponds to (found in dm-dirty-log.h):
+ * uint32_t (*get_region_size)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      uint64_t - contains the region size
+ *
+ * The region size is something that was determined at constructor time.
+ * It is returned in the payload area and 'data_size' is set to
+ * reflect this.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field appropriately.
+ */
+#define DM_ULOG_GET_REGION_SIZE        6
+
+/*
+ * DM_ULOG_IS_CLEAN corresponds to (found in dm-dirty-log.h):
+ * int (*is_clean)(struct dm_dirty_log *log, region_t region);
+ *
+ * Payload-to-userspace:
+ *      uint64_t - the region to get clean status on
+ * Payload-to-kernel:
+ *      int64_t  - 1 if clean, 0 otherwise
+ *
+ * Payload is sizeof(uint64_t) and contains the region for which the clean
+ * status is being made.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - filling the payload with 0 (not clean) or
+ * 1 (clean), setting 'data_size' and 'error' appropriately.
+ */
+#define DM_ULOG_IS_CLEAN               7
+
+/*
+ * DM_ULOG_IN_SYNC corresponds to (found in dm-dirty-log.h):
+ * int (*in_sync)(struct dm_dirty_log *log, region_t region,
+ *                int can_block);
+ *
+ * Payload-to-userspace:
+ *      uint64_t - the region to get sync status on
+ * Payload-to-kernel:
+ *      int64_t - 1 if in-sync, 0 otherwise
+ *
+ * Exactly the same as 'is_clean' above, except this time asking "has the
+ * region been recovered?" vs. "is the region not being modified?"
+ */
+#define DM_ULOG_IN_SYNC                8
+
+/*
+ * DM_ULOG_FLUSH corresponds to (found in dm-dirty-log.h):
+ * int (*flush)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      None.
+ *
+ * No incoming or outgoing payload.  Simply flush log state to disk.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and clearing
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_FLUSH                  9
+
+/*
+ * DM_ULOG_MARK_REGION corresponds to (found in dm-dirty-log.h):
+ * void (*mark_region)(struct dm_dirty_log *log, region_t region);
+ *
+ * Payload-to-userspace:
+ *      uint64_t [] - region(s) to mark
+ * Payload-to-kernel:
+ *      None.
+ *
+ * Incoming payload contains the one or more regions to mark dirty.
+ * The number of regions contained in the payload can be determined from
+ * 'data_size/sizeof(uint64_t)'.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and clearing
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_MARK_REGION           10
+
+/*
+ * DM_ULOG_CLEAR_REGION corresponds to (found in dm-dirty-log.h):
+ * void (*clear_region)(struct dm_dirty_log *log, region_t region);
+ *
+ * Payload-to-userspace:
+ *      uint64_t [] - region(s) to clear
+ * Payload-to-kernel:
+ *      None.
+ *
+ * Incoming payload contains the one or more regions to mark clean.
+ * The number of regions contained in the payload can be determined from
+ * 'data_size/sizeof(uint64_t)'.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and clearing
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_CLEAR_REGION          11
+
+/*
+ * DM_ULOG_GET_RESYNC_WORK corresponds to (found in dm-dirty-log.h):
+ * int (*get_resync_work)(struct dm_dirty_log *log, region_t *region);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      {
+ *              int64_t i; -- 1 if recovery necessary, 0 otherwise
+ *              uint64_t r; -- The region to recover if i=1
+ *      }
+ * 'data_size' should be set appropriately.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field appropriately.
+ */
+#define DM_ULOG_GET_RESYNC_WORK       12
+
+/*
+ * DM_ULOG_SET_REGION_SYNC corresponds to (found in dm-dirty-log.h):
+ * void (*set_region_sync)(struct dm_dirty_log *log,
+ *                         region_t region, int in_sync);
+ *
+ * Payload-to-userspace:
+ *      {
+ *              uint64_t - region to set sync state on
+ *              int64_t  - 0 if not-in-sync, 1 if in-sync
+ *      }
+ * Payload-to-kernel:
+ *      None.
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and clearing
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_SET_REGION_SYNC       13
+
+/*
+ * DM_ULOG_GET_SYNC_COUNT corresponds to (found in dm-dirty-log.h):
+ * region_t (*get_sync_count)(struct dm_dirty_log *log);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      uint64_t - the number of in-sync regions
+ *
+ * No incoming payload.  Kernel-bound payload contains the number of
+ * regions that are in-sync (in a size_t).
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_GET_SYNC_COUNT        14
+
+/*
+ * DM_ULOG_STATUS_INFO corresponds to (found in dm-dirty-log.h):
+ * int (*status)(struct dm_dirty_log *log, STATUSTYPE_INFO,
+ *               char *result, unsigned maxlen);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      Character string containing STATUSTYPE_INFO
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_STATUS_INFO           15
+
+/*
+ * DM_ULOG_STATUS_TABLE corresponds to (found in dm-dirty-log.h):
+ * int (*status)(struct dm_dirty_log *log, STATUSTYPE_TABLE,
+ *               char *result, unsigned maxlen);
+ *
+ * Payload-to-userspace:
+ *      None.
+ * Payload-to-kernel:
+ *      Character string containing STATUSTYPE_TABLE
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_STATUS_TABLE          16
+
+/*
+ * DM_ULOG_IS_REMOTE_RECOVERING corresponds to (found in dm-dirty-log.h):
+ * int (*is_remote_recovering)(struct dm_dirty_log *log, region_t region);
+ *
+ * Payload-to-userspace:
+ *      uint64_t - region to determine recovery status on
+ * Payload-to-kernel:
+ *      {
+ *              int64_t is_recovering;  -- 0 if no, 1 if yes
+ *              uint64_t in_sync_hint;  -- lowest region still needing resync
+ *      }
+ *
+ * When the request has been processed, user-space must return the
+ * dm_ulog_request to the kernel - setting the 'error' field and
+ * 'data_size' appropriately.
+ */
+#define DM_ULOG_IS_REMOTE_RECOVERING  17
+
+/*
+ * (DM_ULOG_REQUEST_MASK & request_type) to get the request type
+ *
+ * Payload-to-userspace:
+ *      A single string containing all the argv arguments separated by ' 's
+ * Payload-to-kernel:
+ *      None.  ('data_size' in the dm_ulog_request struct should be 0.)
+ *
+ * We are reserving 8 bits of the 32-bit 'request_type' field for the
+ * various request types above.  The remaining 24-bits are currently
+ * set to zero and are reserved for future use and compatibility concerns.
+ *
+ * User-space should always use DM_ULOG_REQUEST_TYPE to aquire the
+ * request type from the 'request_type' field to maintain forward compatibility.
+ */
+#define DM_ULOG_REQUEST_MASK 0xFF
+#define DM_ULOG_REQUEST_TYPE(request_type) \
+        (DM_ULOG_REQUEST_MASK & (request_type))
+
+struct dm_ulog_request {
+        char uuid[DM_UUID_LEN]; /* Ties a request to a specific mirror log */
+        char padding[7];        /* Padding because DM_UUID_LEN = 129 */
+
+        int32_t error;          /* Used to report back processing errors */
+
+        uint32_t seq;           /* Sequence number for request */
+        uint32_t request_type;  /* DM_ULOG_* defined above */
+        uint32_t data_size;     /* How much data (not including this struct) */
+
+        char data[0];
+};
+
+#endif /* __DM_LOG_USERSPACE_H__ */