Is there any command-line example to explain how to use this  patch?
I have compiled it and loaded the modules, the '<start><length>' target
parameters in both replicator ant replicator-dev targets means what?
how can I construct these target?
I haven't read the source code in detail till now, sorry.

2009/12/18 <heinzm@redhat.com>

> From: Heinz Mauelshagen <heinzm@redhat.com>
>
> The dm-registry module is a general purpose registry for modules.
>
> The remote replicator utilizes it to register its ringbuffer log and
> site link handlers in order to avoid duplicating registry code and logic.
>
>
> Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
> Reviewed-by: Jon Brassow <jbrassow@redhat.com>
> Tested-by: Jon Brassow <jbrassow@redhat.com>
> ---
>  Documentation/device-mapper/replicator.txt |  203
> +++++++++++++++++++++++++
>  drivers/md/Kconfig                         |    8 +
>  drivers/md/Makefile                        |    1 +
>  drivers/md/dm-registry.c                   |  224
> ++++++++++++++++++++++++++++
>  drivers/md/dm-registry.h                   |   38 +++++
>  5 files changed, 474 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/device-mapper/replicator.txt
>  create mode 100644 drivers/md/dm-registry.c
>  create mode 100644 drivers/md/dm-registry.h
>
> diff --git 2.6.33-rc1.orig/Documentation/device-mapper/replicator.txt
> 2.6.33-rc1/Documentation/device-mapper/replicator.txt
> new file mode 100644
> index 0000000..1d408a6
> --- /dev/null
> +++ 2.6.33-rc1/Documentation/device-mapper/replicator.txt
> @@ -0,0 +1,203 @@
> +dm-replicator
> +=============
> +
> +Device-mapper replicator is designed to enable redundant copies of
> +storage devices to be made - preferentially, to remote locations.
> +RAID1 (aka mirroring) is often used to maintain redundant copies of
> +storage for fault tolerance purposes.  Unlike RAID1, which often
> +assumes similar device characteristics, dm-replicator is designed to
> +handle devices with different latency and bandwidth characteristics
> +which are often the result of the geograhic disparity of multi-site
> +architectures.  Simply put, you might choose RAID1 to protect from
> +a single device failure, but you would choose remote replication
> +via dm-replicator for protection against a site failure.
> +
> +dm-replicator works by first sending write requests to the "replicator
> +log".  Not to be confused with the device-mapper dirty log, this
> +replicator log behaves similarly to that of a journal.  Write requests
> +go to this log first and then are copied to all the replicate devices
> +at their various locations.  Requests are cleared from the log once all
> +replicate devices confirm the data is received/copied.  This architecture
> +allows dm-replicator to be flexible in terms of device characteristics.
> +If one device should fall behind the others - perhaps due to high latency
> -
> +the slack is picked up by the log.  The user has a great deal of
> +flexibility in specifying to what degree a particular site is allowed to
> +fall behind - if at all.
> +
> +Device-Mapper's dm-replicator has two targets, "replicator" and
> +"replicator-dev".  The "replicator" target is used to setup the
> +aforementioned log and allow the specification of site link properties.
> +Through the "replicator" target, the user might specify that writes
> +that are copied to the local site must happen synchronously (i.e the
> +writes are complete only after they have passed through the log device
> +and have landed on the local site's disk).  They may also specify that
> +a remote link should asynchronously complete writes, but that the remote
> +link should never fall more than 100MB behind in terms of processing.
> +Again, the "replicator" target is used to define the replicator log and
> +the characteristics of each site link.
> +
> +The "replicator-dev" target is used to define the devices used and
> +associate them with a particular replicator log.  You might think of
> +this stage in a similar way to setting up RAID1 (mirroring).  You
> +define a set of devices which will be copies of each other, but
> +access the device through the mirror virtual device which takes care
> +of the copying.  The user accessible replicator device is analogous
> +to the mirror virtual device, while the set of devices being copied
> +to are analogous to the mirror images (sometimes called 'legs').
> +When creating a replicator device via the "replicator-dev" target,
> +it must be associated with the replicator log (created with the
> +aforementioned "replicator" target).  When each redundant device
> +is specified as part of the replicator device, it is associated with
> +a site link whose properties were defined when the "replicator"
> +target was created.
> +
> +The user can go farther than simply replicating one device.  They
> +can continue to add replicator devices - associating them with a
> +particular replicator log.  Writes that go through the replicator
> +log are guarenteed to have their write ordering preserved.  So, if
> +you associate more than one replicator device to a particular
> +replicator log, you are preserving write ordering across multiple
> +devices.  This might be useful if you had a database that spanned
> +multiple disks and write ordering must be preserved or any transaction
> +accounting scheme would be foiled.  (You can imagine this like
> +preserving write ordering across a number of mirrored devices, where
> +each mirror has images/legs in different geographic locations.)
> +
> +dm-replicator has a modular architecture.  Future implementations for
> +the replicator log and site link modules are allowed.  The current
> +replication log is ringbuffer - utilized to store all writes being
> +subject to replication and enforce write ordering.  The current site
> +link code is based on accessing block devices (iSCSI, FC, etc) and
> +does device recovery including (initial) resynchronization.
> +
> +
> +Picture of a 2 site configuration with 3 local devices (LDs) in a
> +primary site being resycnhronied to 3 remotes sites with 3 remote
> +devices (RDs) each via site links (SLINK) 1-2 with site link 0
> +as a special case to handle the local devices:
> +
> +                                           |
> +    Local (primary) site                   |      Remote sites
> +    --------------------                   |      ------------
> +                                           |
> +    D1   D2     Dn                         |
> +     |   |       |                         |
> +     +---+- ... -+                         |
> +         |                                 |
> +       REPLOG-----------------+- SLINK1 ------------+
> +         |                    |            |        |
> +       SLINK0 (special case)  |            |        |
> +         |                    |            |        |
> +     +-----+   ...  +         |            |   +----+- ... -+
> +     |     |        |         |            |   |    |       |
> +    LD1   LD2      LDn        |            |  RD1  RD2     RDn
> +                              |            |
> +                              +-- SLINK2------------+
> +                              |            |        |
> +                              |            |   +----+- ... -+
> +                              |            |   |    |       |
> +                              |            |  RD1  RD2     RDn
> +                              |            |
> +                              |            |
> +                              |            |
> +                              +- SLINKm ------------+
> +                                           |        |
> +                                           |   +----+- ... -+
> +                                           |   |    |       |
> +                                           |  RD1  RD2     RDn
> +
> +
> +
> +
> +The following are descriptions of the device-mapper tables used to
> +construct the "replicator" and "replicator-dev" targets.
> +
> +"replicator" target parameters:
> +-------------------------------
> +<start> <length> replicator \
> +       <replog_type> <#replog_params> <replog_params> \
> +       [<slink_type_0> <#slink_params_0> <slink_params_0>]{1..N}
> +
> +<replog_type>    = "ringbuffer" is currently the only available type
> +<#replog_params> = # of args following this one intended for the replog (2
> or 4)
> +<replog_params>  = <dev_path> <dev_start> [auto/create/open <size>]
> +       <dev_path>  = device path of replication log (REPLOG) backing store
> +       <dev_start> = offset to REPLOG header
> +       create      = The replication log will be initialized if not active
> +                     and sized to "size".  (If already active, the create
> +                     will fail.)  Size is always in sectors.
> +       open        = The replication log must be initialized and valid or
> +                     the constructor will fail.
> +       auto        = If a valid replication log header is found on the
> +                     replication device, this will behave like 'open'.
> +                     Otherwise, this option behaves like 'create'.
> +
> +<slink_type>    = "blockdev" is currently the only available type
> +<#slink_params> = 1/2/4
> +<slink_params>  = <slink_nr> [<slink_policy> [<fall_behind> <N>]]
> +       <slink_nr>     = This is a unique number that is used to identify a
> +                        particular site/location.  '0' is always used to
> +                        identify the local site, while increasing integers
> +                        are used to identify remote sites.
> +       <slink_policy> = The policy can be either 'sync' or 'async'.
> +                        'sync' means write requests will not return until
> +                        the data is on the storage device.  'async' allows
> +                        a device to "fall behind"; that is, outstanding
> +                        write requests are waiting in the replication log
> +                        to be processed for this site, but it is not
> delaying
> +                        the writes of other sites.
> +       <fall_behind>  = This field is used to specify how far the user is
> +                        willing to allow write requests to this specific
> site
> +                        to "fall behind" in processing before switching to
> +                        a 'sync' policy.  This "fall behind" threshhold
> can
> +                        be specified in three ways: ios, size, or timeout.
> +                        'ios' is the number of pending I/Os allowed (e.g.
> +                        "ios 10000").  'size' is the amount of pending
> data
> +                        allowed (e.g. "size 200m").  Size labels include:
> +                        s (sectors), k, m, g, t, p, and e.  'timeout' is
> +                        the amount of time allowed for writes to be
> +                        outstanding.  Time labels include: s, m, h, and d.
> +
> +
> +"replicator-dev" target parameters:
> +-----------------------------------
> +start> <length> replicator-dev
> +       <replicator_device> <dev_nr> \
> +       [<slink_nr> <#dev_params> <dev_params>
> +        <dlog_type> <#dlog_params> <dlog_params>]{1..N}
> +
> +<replicator_device> = device previously constructed via "replication"
> target
> +<dev_nr>           = An integer that is used to 'tag' write requests as
> +                     belonging to a particular set of devices -
> specifically,
> +                     the devices that follow this argument (i.e. the site
> +                     link devices).
> +<slink_nr>         = This number identifies the site/location where the
> next
> +                     device to be specified comes from.  It is exactly the
> +                     same number used to identify the site/location (and
> its
> +                     policies) in the "replicator" target.  Interestingly,
> +                     while one might normally expect a "dev_type" argument
> +                     here, it can be deduced from the site link number and
> +                     the 'slink_type' given in the "replication" target.
> +<#dev_params>      = '1'  (The number of allowed parameters actually
> depends
> +                     on the 'slink_type' given in the "replication"
> target.
> +                     Since our only option there is "blockdev", the only
> +                     allowable number here is currently '1'.)
> +<dev_params>       = 'dev_path'  (Again, since "blockdev" is the only
> +                     'slink_type' available, the only allowable argument
> here
> +                     is the path to the device.)
> +<dlog_type>        = Not to be confused with the "replicator log", this is
> +                     the type of dirty log associated with this particular
> +                     device.  Dirty logs are used for synchronization,
> during
> +                     initialization or fall behind conditions, to bring
> devices
> +                     into a coherent state with its peers - analogous to
> +                     rebuilding a RAID1 (mirror) device.  Available dirty
> +                     log types include: 'nolog', 'core', and 'disk'
> +<#dlog_params>     = The number of arguments required for a particular log
> +                     type - 'nolog' = 0, 'core' = 1/2, 'disk' = 2/3.
> +<dlog_params>      = 'nolog' => ~no arguments~
> +                     'core'  => <region_size> [sync | nosync]
> +                     'disk'  => <dlog_dev_path> <region_size> [sync |
> nosync]
> +       <region_size>   = This sets the granularity at which the dirty log
> +                         tracks what areas of the device is in-sync.
> +       [sync | nosync] = Optionally specify whether the sync should be
> forced
> +                         or avoided initially.
> diff --git 2.6.33-rc1.orig/drivers/md/Kconfig 2.6.33-rc1/drivers/md/Kconfig
> index acb3a4e..62c9766 100644
> --- 2.6.33-rc1.orig/drivers/md/Kconfig
> +++ 2.6.33-rc1/drivers/md/Kconfig
> @@ -313,6 +313,14 @@ config DM_DELAY
>
>        If unsure, say N.
>
> +config DM_REPLICATOR
> +       tristate "Replication target (EXPERIMENTAL)"
> +       depends on BLK_DEV_DM && EXPERIMENTAL
> +       ---help---
> +       A target that supports replication of local devices to remote
> sites.
> +
> +       If unsure, say N.
> +
>  config DM_UEVENT
>        bool "DM uevents (EXPERIMENTAL)"
>        depends on BLK_DEV_DM && EXPERIMENTAL
> diff --git 2.6.33-rc1.orig/drivers/md/Makefile
> 2.6.33-rc1/drivers/md/Makefile
> index e355e7f..be05b39 100644
> --- 2.6.33-rc1.orig/drivers/md/Makefile
> +++ 2.6.33-rc1/drivers/md/Makefile
> @@ -44,6 +44,7 @@ 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
> +obj-$(CONFIG_DM_REPLICATOR)    += dm-log.o dm-registry.o
>
>  quiet_cmd_unroll = UNROLL  $@
>       cmd_unroll = $(AWK) -f$(srctree)/$(src)/unroll.awk -vN=$(UNROLL) \
> diff --git 2.6.33-rc1.orig/drivers/md/dm-registry.c
> 2.6.33-rc1/drivers/md/dm-registry.c
> new file mode 100644
> index 0000000..fb8abbf
> --- /dev/null
> +++ 2.6.33-rc1/drivers/md/dm-registry.c
> @@ -0,0 +1,224 @@
> +/*
> + * Copyright (C) 2009 Red Hat, Inc. All rights reserved.
> + *
> + * Module Author: Heinz Mauelshagen (heinzm@redhat.com)
> + *
> + * Generic registry for arbitrary structures
> + * (needs dm_registry_type structure upfront each registered structure).
> + *
> + * This file is released under the GPL.
> + *
> + * FIXME: use as registry for e.g. dirty log types as well.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +
> +#include "dm-registry.h"
> +
> +#define        DM_MSG_PREFIX   "dm-registry"
> +
> +static const char *version = "0.001";
> +
> +/* Sizable class registry. */
> +static unsigned num_classes;
> +static struct list_head *_classes;
> +static rwlock_t *_locks;
> +
> +void *
> +dm_get_type(const char *type_name, enum dm_registry_class class)
> +{
> +       struct dm_registry_type *t;
> +
> +       read_lock(_locks + class);
> +       list_for_each_entry(t, _classes + class, list) {
> +               if (!strcmp(type_name, t->name)) {
> +                       if (!t->use_count && !try_module_get(t->module)) {
> +                               read_unlock(_locks + class);
> +                               return ERR_PTR(-ENOMEM);
> +                       }
> +
> +                       t->use_count++;
> +                       read_unlock(_locks + class);
> +                       return t;
> +               }
> +       }
> +
> +       read_unlock(_locks + class);
> +       return ERR_PTR(-ENOENT);
> +}
> +EXPORT_SYMBOL(dm_get_type);
> +
> +void
> +dm_put_type(void *type, enum dm_registry_class class)
> +{
> +       struct dm_registry_type *t = type;
> +
> +       read_lock(_locks + class);
> +       if (!--t->use_count)
> +               module_put(t->module);
> +
> +       read_unlock(_locks + class);
> +}
> +EXPORT_SYMBOL(dm_put_type);
> +
> +/* Add a type to the registry. */
> +int
> +dm_register_type(void *type, enum dm_registry_class class)
> +{
> +       struct dm_registry_type *t = type, *tt;
> +
> +       if (unlikely(class >= num_classes))
> +               return -EINVAL;
> +
> +       tt = dm_get_type(t->name, class);
> +       if (unlikely(!IS_ERR(tt))) {
> +               dm_put_type(t, class);
> +               return -EEXIST;
> +       }
> +
> +       write_lock(_locks + class);
> +       t->use_count = 0;
> +       list_add(&t->list, _classes + class);
> +       write_unlock(_locks + class);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(dm_register_type);
> +
> +/* Remove a type from the registry. */
> +int
> +dm_unregister_type(void *type, enum dm_registry_class class)
> +{
> +       struct dm_registry_type *t = type;
> +
> +       if (unlikely(class >= num_classes)) {
> +               DMERR("Attempt to unregister invalid class");
> +               return -EINVAL;
> +       }
> +
> +       write_lock(_locks + class);
> +
> +       if (unlikely(t->use_count)) {
> +               write_unlock(_locks + class);
> +               DMWARN("Attempt to unregister a type that is still in
> use");
> +               return -ETXTBSY;
> +       } else
> +               list_del(&t->list);
> +
> +       write_unlock(_locks + class);
> +       return 0;
> +}
> +EXPORT_SYMBOL(dm_unregister_type);
> +
> +/*
> + * Return kmalloc'ed NULL terminated pointer
> + * array of all type names of the given class.
> + *
> + * Caller has to kfree the array!.
> + */
> +const char **dm_types_list(enum dm_registry_class class)
> +{
> +       unsigned i = 0, count = 0;
> +       const char **r;
> +       struct dm_registry_type *t;
> +
> +       /* First count the registered types in the class. */
> +       read_lock(_locks + class);
> +       list_for_each_entry(t, _classes + class, list)
> +               count++;
> +       read_unlock(_locks + class);
> +
> +       /* None registered in this class. */
> +       if (!count)
> +               return NULL;
> +
> +       /* One member more for array NULL termination. */
> +       r = kzalloc((count + 1) * sizeof(*r), GFP_KERNEL);
> +       if (!r)
> +               return ERR_PTR(-ENOMEM);
> +
> +       /*
> +        * Go with the counted ones.
> +        * Any new added ones after we counted will be ignored!
> +        */
> +       read_lock(_locks + class);
> +       list_for_each_entry(t, _classes + class, list) {
> +               r[i++] = t->name;
> +               if (!--count)
> +                       break;
> +       }
> +       read_unlock(_locks + class);
> +
> +       return r;
> +}
> +EXPORT_SYMBOL(dm_types_list);
> +
> +int __init
> +dm_registry_init(void)
> +{
> +       unsigned n;
> +
> +       BUG_ON(_classes);
> +       BUG_ON(_locks);
> +
> +       /* Module parameter given ? */
> +       if (!num_classes)
> +               num_classes = DM_REGISTRY_CLASS_END;
> +
> +       n = num_classes;
> +       _classes = kmalloc(n * sizeof(*_classes), GFP_KERNEL);
> +       if (!_classes) {
> +               DMERR("Failed to allocate classes registry");
> +               return -ENOMEM;
> +       }
> +
> +       _locks = kmalloc(n * sizeof(*_locks), GFP_KERNEL);
> +       if (!_locks) {
> +               DMERR("Failed to allocate classes locks");
> +               kfree(_classes);
> +               _classes = NULL;
> +               return -ENOMEM;
> +       }
> +
> +       while (n--) {
> +               INIT_LIST_HEAD(_classes + n);
> +               rwlock_init(_locks + n);
> +       }
> +
> +       DMINFO("initialized %s for max %u classes", version, num_classes);
> +       return 0;
> +}
> +
> +void __exit
> +dm_registry_exit(void)
> +{
> +       BUG_ON(!_classes);
> +       BUG_ON(!_locks);
> +
> +       kfree(_classes);
> +       _classes = NULL;
> +       kfree(_locks);
> +       _locks = NULL;
> +       DMINFO("exit %s", version);
> +}
> +
> +/* Module hooks */
> +module_init(dm_registry_init);
> +module_exit(dm_registry_exit);
> +module_param(num_classes, uint, 0);
> +MODULE_PARM_DESC(num_classes, "Maximum number of classes");
> +MODULE_DESCRIPTION(DM_NAME "device-mapper registry");
> +MODULE_AUTHOR("Heinz Mauelshagen <heinzm@redhat.com>");
> +MODULE_LICENSE("GPL");
> +
> +#ifndef MODULE
> +static int __init num_classes_setup(char *str)
> +{
> +       num_classes = simple_strtol(str, NULL, 0);
> +       return num_classes ? 1 : 0;
> +}
> +
> +__setup("num_classes=", num_classes_setup);
> +#endif
> diff --git 2.6.33-rc1.orig/drivers/md/dm-registry.h
> 2.6.33-rc1/drivers/md/dm-registry.h
> new file mode 100644
> index 0000000..1cb0ce8
> --- /dev/null
> +++ 2.6.33-rc1/drivers/md/dm-registry.h
> @@ -0,0 +1,38 @@
> +/*
> + * Copyright (C) 2009 Red Hat, Inc. All rights reserved.
> + *
> + * Module Author: Heinz Mauelshagen (heinzm@redhat.com)
> + *
> + * Generic registry for arbitrary structures.
> + * (needs dm_registry_type structure upfront each registered structure).
> + *
> + * This file is released under the GPL.
> + */
> +
> +#include "dm.h"
> +
> +#ifndef DM_REGISTRY_H
> +#define DM_REGISTRY_H
> +
> +enum dm_registry_class {
> +       DM_REPLOG = 0,
> +       DM_SLINK,
> +       DM_LOG,
> +       DM_REGION_HASH,
> +       DM_REGISTRY_CLASS_END,
> +};
> +
> +struct dm_registry_type {
> +       struct list_head list;  /* Linked list of types in this class. */
> +       const char *name;
> +       struct module *module;
> +       unsigned int use_count;
> +};
> +
> +void *dm_get_type(const char *type_name, enum dm_registry_class class);
> +void dm_put_type(void *type, enum dm_registry_class class);
> +int dm_register_type(void *type, enum dm_registry_class class);
> +int dm_unregister_type(void *type, enum dm_registry_class class);
> +const char **dm_types_list(enum dm_registry_class class);
> +
> +#endif
> --
> 1.6.2.5
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>