This patch adds the dm-clone target, which allows cloning of arbitrary block devices. dm-clone produces a one-to-one copy of an existing, read-only source device into a writable destination device: It presents a virtual block device which makes all data appear immediately, and redirects reads and writes accordingly. The main use case of dm-clone is to clone a potentially remote, high-latency, read-only, archival-type block device into a writable, fast, primary-type device for fast, low-latency I/O. The cloned device is visible/mountable immediately and the copy of the source device to the destination device happens in the background, in parallel with user I/O. For example, one could restore an application backup from a read-only copy, accessible through a network storage protocol (NBD, Fibre Channel, iSCSI, AoE, etc.), into a local SSD or NVMe device, and start using the device immediately, without waiting for the restore to complete. When the cloning completes, the dm-clone table can be removed altogether and be replaced, e.g., by a linear table, mapping directly to the destination device. dm-clone is optimized for small, random writes, with size equal to dm-clone's region size, e.g., 4K. For more information regarding dm-clone's operation, please read the attached documentation. A preliminary test suite for dm-clone can be found at https://github.com/arrikto/device-mapper-test-suite/tree/feature-dm-clone Changes in v2: - Remove needless empty newlines. - Use the term "region" consistently and never call it a block. - Rename "origin" device to "source" device and "clone" device to "destination" device. - Express "hydration_threshold" in multiples of a region. - Rename "hydration_block_size" to "hydration_batch_size" and express it in multiples of a region. - Add missing "static" keyword to __load_bitset_in_core() and __metadata_commit(). - clone_message(): Don't print misleading error message about "unsupported message" in case of correct messages with wrong number of arguments. - Rename module parameter "clone_copy_throttle" to "clone_hydration_throttle" to be consistent with its description. I also updated the test suite to reflect these changes. v1: https://www.redhat.com/archives/dm-devel/2019-July/msg00088.html Nikos Tsironis (1): dm: add clone target Documentation/device-mapper/dm-clone.rst | 333 +++++ drivers/md/Kconfig | 14 + drivers/md/Makefile | 2 + drivers/md/dm-clone-metadata.c | 963 +++++++++++++ drivers/md/dm-clone-metadata.h | 158 +++ drivers/md/dm-clone-target.c | 2190 ++++++++++++++++++++++++++++++ 6 files changed, 3660 insertions(+) create mode 100644 Documentation/device-mapper/dm-clone.rst create mode 100644 drivers/md/dm-clone-metadata.c create mode 100644 drivers/md/dm-clone-metadata.h create mode 100644 drivers/md/dm-clone-target.c -- 2.11.0 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
