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authorYunhong Jiang <yunhong.jiang@intel.com>2015-08-04 12:17:53 -0700
committerYunhong Jiang <yunhong.jiang@intel.com>2015-08-04 15:44:42 -0700
commit9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 (patch)
tree1c9cafbcd35f783a87880a10f85d1a060db1a563 /kernel/Documentation/blockdev/drbd/data-structure-v9.txt
parent98260f3884f4a202f9ca5eabed40b1354c489b29 (diff)
Add the rt linux 4.1.3-rt3 as base
Import the rt linux 4.1.3-rt3 as OPNFV kvm base. It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and the base is: commit 0917f823c59692d751951bf5ea699a2d1e2f26a2 Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Sat Jul 25 12:13:34 2015 +0200 Prepare v4.1.3-rt3 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> We lose all the git history this way and it's not good. We should apply another opnfv project repo in future. Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423 Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>
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+This describes the in kernel data structure for DRBD-9. Starting with
+Linux v3.14 we are reorganizing DRBD to use this data structure.
+
+Basic Data Structure
+====================
+
+A node has a number of DRBD resources. Each such resource has a number of
+devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD
+device is represented by a block device locally.
+
+The DRBD objects are interconnected to form a matrix as depicted below; a
+drbd_peer_device object sits at each intersection between a drbd_device and a
+drbd_connection:
+
+ /--------------+---------------+.....+---------------\
+ | resource | device | | device |
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ +--------------+---------------+.....+---------------+
+ : : : : :
+ : : : : :
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ \--------------+---------------+.....+---------------/
+
+In this table, horizontally, devices can be accessed from resources by their
+volume number. Likewise, peer_devices can be accessed from connections by
+their volume number. Objects in the vertical direction are connected by double
+linked lists. There are back pointers from peer_devices to their connections a
+devices, and from connections and devices to their resource.
+
+All resources are in the drbd_resources double-linked list. In addition, all
+devices can be accessed by their minor device number via the drbd_devices idr.
+
+The drbd_resource, drbd_connection, and drbd_device objects are reference
+counted. The peer_device objects only serve to establish the links between
+devices and connections; their lifetime is determined by the lifetime of the
+device and connection which they reference.