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Re: [dm-devel] [PATCH v6 1/4] dm-replicator: documentation and module registry



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

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