From: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Jon Brassow <jbrassow@xxxxxxxxxx>
Tested-by: Jon Brassow <jbrassow@xxxxxxxxxx>
---
Documentation/device-mapper/replicator.txt | 203 +++++++++++++++++++++++++
drivers/md/dm-registry.c | 224 ++++++++++++++++++++++++++++
drivers/md/dm-registry.h | 38 +++++
3 files changed, 465 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 linux-2.6.orig/Documentation/device-mapper/replicator.txt linux-2.6/Documentation/device-mapper/replicator.txt
new file mode 100644
index 0000000..1d408a6
--- /dev/null
+++ linux-2.6/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 linux-2.6.orig/drivers/md/dm-registry.c linux-2.6/drivers/md/dm-registry.c
new file mode 100644
index 0000000..1108aa0
--- /dev/null
+++ linux-2.6/drivers/md/dm-registry.c
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
+ *
+ * Module Author: Heinz Mauelshagen (heinzm@xxxxxxxxxx)
+ *
+ * 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@xxxxxxxxxx>");
+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 linux-2.6.orig/drivers/md/dm-registry.h linux-2.6/drivers/md/dm-registry.h
new file mode 100644
index 0000000..2d04314
--- /dev/null
+++ linux-2.6/drivers/md/dm-registry.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
+ *
+ * Module Author: Heinz Mauelshagen (Mauelshagen@xxxxxxxxxx)
+ *
+ * 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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