Revert "device-mapper: Add dm-bow"

The dm-bow kernel module (developed externally by Google team) has been
moved to linux-tizen-modules-source repository, so keeping a copy of it
in each kernel repository is not needed anymore.

This reverts commit 540ba0d4e89eec45ddd9d41030fb6cf10392b42a.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Change-Id: I862b493f66319a651402067a1e81ac7119d5ebdf

1 files changed, 0 insertions, 99 deletions

diff --git a/Documentation/device-mapper/dm-bow.txt b/Documentation/device-mapper/dm-bow.txt
deleted file mode 100644
index e3fc4d22e0f4..000000000000
--- a/Documentation/device-mapper/dm-bow.txt
+++ /dev/null
@@ -1,99 +0,0 @@
-dm_bow (backup on write)
-========================
-
-dm_bow is a device mapper driver that uses the free space on a device to back up
-data that is overwritten. The changes can then be committed by a simple state
-change, or rolled back by removing the dm_bow device and running a command line
-utility over the underlying device.
-
-dm_bow has three states, set by writing ‘1’ or ‘2’ to /sys/block/dm-?/bow/state.
-It is only possible to go from state 0 (initial state) to state 1, and then from
-state 1 to state 2.
-
-State 0: dm_bow collects all trims to the device and assumes that these mark
-free space on the overlying file system that can be safely used. Typically the
-mount code would create the dm_bow device, mount the file system, call the
-FITRIM ioctl on the file system then switch to state 1. These trims are not
-propagated to the underlying device.
-
-State 1: All writes to the device cause the underlying data to be backed up to
-the free (trimmed) area as needed in such a way as they can be restored.
-However, the writes, with one exception, then happen exactly as they would
-without dm_bow, so the device is always in a good final state. The exception is
-that sector 0 is used to keep a log of the latest changes, both to indicate that
-we are in this state and to allow rollback. See below for all details. If there
-isn't enough free space, writes are failed with -ENOSPC.
-
-State 2: The transition to state 2 triggers replacing the special sector 0 with
-the normal sector 0, and the freeing of all state information. dm_bow then
-becomes a pass-through driver, allowing the device to continue to be used with
-minimal performance impact.
-
-Usage
-=====
-dm-bow takes one command line parameter, the name of the underlying device.
-
-dm-bow will typically be used in the following way. dm-bow will be loaded with a
-suitable underlying device and the resultant device will be mounted. A file
-system trim will be issued via the FITRIM ioctl, then the device will be
-switched to state 1. The file system will now be used as normal. At some point,
-the changes can either be committed by switching to state 2, or rolled back by
-unmounting the file system, removing the dm-bow device and running the command
-line utility. Note that rebooting the device will be equivalent to unmounting
-and removing, but the command line utility must still be run
-
-Details of operation in state 1
-===============================
-
-dm_bow maintains a type for all sectors. A sector can be any of:
-
-SECTOR0
-SECTOR0_CURRENT
-UNCHANGED
-FREE
-CHANGED
-BACKUP
-
-SECTOR0 is the first sector on the device, and is used to hold the log of
-changes. This is the one exception.
-
-SECTOR0_CURRENT is a sector picked from the FREE sectors, and is where reads and
-writes from the true sector zero are redirected to. Note that like any backup
-sector, if the sector is written to directly, it must be moved again.
-
-UNCHANGED means that the sector has not been changed since we entered state 1.
-Thus if it is written to or trimmed, the contents must first be backed up.
-
-FREE means that the sector was trimmed in state 0 and has not yet been written
-to or used for backup. On being written to, a FREE sector is changed to CHANGED.
-
-CHANGED means that the sector has been modified, and can be further modified
-without further backup.
-
-BACKUP means that this is a free sector being used as a backup. On being written
-to, the contents must first be backed up again.
-
-All backup operations are logged to the first sector. The log sector has the
-format:
---------------------------------------------------------
-| Magic | Count | Sequence | Log entry | Log entry | …
---------------------------------------------------------
-
-Magic is a magic number. Count is the number of log entries. Sequence is 0
-initially. A log entry is
-
------------------------------------
-| Source | Dest | Size | Checksum |
------------------------------------
-
-When SECTOR0 is full, the log sector is backed up and another empty log sector
-created with sequence number one higher. The first entry in any log entry with
-sequence > 0 therefore must be the log of the backing up of the previous log
-sector. Note that sequence is not strictly needed, but is a useful sanity check
-and potentially limits the time spent trying to restore a corrupted snapshot.
-
-On entering state 1, dm_bow has a list of free sectors. All other sectors are
-unchanged. Sector0_current is selected from the free sectors and the contents of
-sector 0 are copied there. The sector 0 is backed up, which triggers the first
-log entry to be written.
-