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 device (origin) into a writable device (clone): 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 origin device to the clone 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 clone device. dm-clone is optimized for small, random writes, with size equal to dm-clone's block/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 Nikos Tsironis (1): dm: add clone target Documentation/device-mapper/dm-clone.rst | 334 +++++ drivers/md/Kconfig | 13 + drivers/md/Makefile | 2 + drivers/md/dm-clone-metadata.c | 991 +++++++++++++ drivers/md/dm-clone-metadata.h | 158 +++ drivers/md/dm-clone-target.c | 2244 ++++++++++++++++++++++++++++++ 6 files changed, 3742 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
