[Feature]add MT2731_MP2_MR2_SVN388 baseline version
Change-Id: Ief04314834b31e27effab435d3ca8ba33b499059
diff --git a/src/kernel/linux/v4.14/Documentation/device-mapper/switch.txt b/src/kernel/linux/v4.14/Documentation/device-mapper/switch.txt
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+dm-switch
+=========
+
+The device-mapper switch target creates a device that supports an
+arbitrary mapping of fixed-size regions of I/O across a fixed set of
+paths. The path used for any specific region can be switched
+dynamically by sending the target a message.
+
+It maps I/O to underlying block devices efficiently when there is a large
+number of fixed-sized address regions but there is no simple pattern
+that would allow for a compact representation of the mapping such as
+dm-stripe.
+
+Background
+----------
+
+Dell EqualLogic and some other iSCSI storage arrays use a distributed
+frameless architecture. In this architecture, the storage group
+consists of a number of distinct storage arrays ("members") each having
+independent controllers, disk storage and network adapters. When a LUN
+is created it is spread across multiple members. The details of the
+spreading are hidden from initiators connected to this storage system.
+The storage group exposes a single target discovery portal, no matter
+how many members are being used. When iSCSI sessions are created, each
+session is connected to an eth port on a single member. Data to a LUN
+can be sent on any iSCSI session, and if the blocks being accessed are
+stored on another member the I/O will be forwarded as required. This
+forwarding is invisible to the initiator. The storage layout is also
+dynamic, and the blocks stored on disk may be moved from member to
+member as needed to balance the load.
+
+This architecture simplifies the management and configuration of both
+the storage group and initiators. In a multipathing configuration, it
+is possible to set up multiple iSCSI sessions to use multiple network
+interfaces on both the host and target to take advantage of the
+increased network bandwidth. An initiator could use a simple round
+robin algorithm to send I/O across all paths and let the storage array
+members forward it as necessary, but there is a performance advantage to
+sending data directly to the correct member.
+
+A device-mapper table already lets you map different regions of a
+device onto different targets. However in this architecture the LUN is
+spread with an address region size on the order of 10s of MBs, which
+means the resulting table could have more than a million entries and
+consume far too much memory.
+
+Using this device-mapper switch target we can now build a two-layer
+device hierarchy:
+
+ Upper Tier - Determine which array member the I/O should be sent to.
+ Lower Tier - Load balance amongst paths to a particular member.
+
+The lower tier consists of a single dm multipath device for each member.
+Each of these multipath devices contains the set of paths directly to
+the array member in one priority group, and leverages existing path
+selectors to load balance amongst these paths. We also build a
+non-preferred priority group containing paths to other array members for
+failover reasons.
+
+The upper tier consists of a single dm-switch device. This device uses
+a bitmap to look up the location of the I/O and choose the appropriate
+lower tier device to route the I/O. By using a bitmap we are able to
+use 4 bits for each address range in a 16 member group (which is very
+large for us). This is a much denser representation than the dm table
+b-tree can achieve.
+
+Construction Parameters
+=======================
+
+ <num_paths> <region_size> <num_optional_args> [<optional_args>...]
+ [<dev_path> <offset>]+
+
+<num_paths>
+ The number of paths across which to distribute the I/O.
+
+<region_size>
+ The number of 512-byte sectors in a region. Each region can be redirected
+ to any of the available paths.
+
+<num_optional_args>
+ The number of optional arguments. Currently, no optional arguments
+ are supported and so this must be zero.
+
+<dev_path>
+ The block device that represents a specific path to the device.
+
+<offset>
+ The offset of the start of data on the specific <dev_path> (in units
+ of 512-byte sectors). This number is added to the sector number when
+ forwarding the request to the specific path. Typically it is zero.
+
+Messages
+========
+
+set_region_mappings <index>:<path_nr> [<index>]:<path_nr> [<index>]:<path_nr>...
+
+Modify the region table by specifying which regions are redirected to
+which paths.
+
+<index>
+ The region number (region size was specified in constructor parameters).
+ If index is omitted, the next region (previous index + 1) is used.
+ Expressed in hexadecimal (WITHOUT any prefix like 0x).
+
+<path_nr>
+ The path number in the range 0 ... (<num_paths> - 1).
+ Expressed in hexadecimal (WITHOUT any prefix like 0x).
+
+R<n>,<m>
+ This parameter allows repetitive patterns to be loaded quickly. <n> and <m>
+ are hexadecimal numbers. The last <n> mappings are repeated in the next <m>
+ slots.
+
+Status
+======
+
+No status line is reported.
+
+Example
+=======
+
+Assume that you have volumes vg1/switch0 vg1/switch1 vg1/switch2 with
+the same size.
+
+Create a switch device with 64kB region size:
+ dmsetup create switch --table "0 `blockdev --getsz /dev/vg1/switch0`
+ switch 3 128 0 /dev/vg1/switch0 0 /dev/vg1/switch1 0 /dev/vg1/switch2 0"
+
+Set mappings for the first 7 entries to point to devices switch0, switch1,
+switch2, switch0, switch1, switch2, switch1:
+ dmsetup message switch 0 set_region_mappings 0:0 :1 :2 :0 :1 :2 :1
+
+Set repetitive mapping. This command:
+ dmsetup message switch 0 set_region_mappings 1000:1 :2 R2,10
+is equivalent to:
+ dmsetup message switch 0 set_region_mappings 1000:1 :2 :1 :2 :1 :2 :1 :2 \
+ :1 :2 :1 :2 :1 :2 :1 :2 :1 :2
+