Hi I annouce that I released the first version of a patch set that makes it possible to use SCSI XCOPY offload for the block layer and device mapper. The patchset is at http://people.redhat.com/~mpatocka/patches/kernel/xcopy/series.html It requires kernel version at least 3.16-rc4. It was tested on target-core iSCSI implementation. It is based on Martin Petersen's work https://git.kernel.org/cgit/linux/kernel/git/mkp/linux.git/commit/?h=xcopy&id=0bdeed274e16b3038a851552188512071974eea8, but it is changed significantly so that it is possible to propagate XCOPY bios through the device mapper stack. The basic architecture is this: in the function blkdev_issue_copy we create two bios, one for read and one for write (with bi_rw READ|REQ_COPY and WRITE|REQ_COPY). Both bios have a pointer to the same bio_copy structure. These two bios travel independently through the device mapper stack - each bio can go through different device mapper devices. When both the bios reach the physical block device (in the function blk_queue_bio) the bio pair is collected and a XCOPY request is allocated and sent to the scsi disk driver. Note that because device mapper mapping can dynamically change, there no guarantee that the XCOPY command succeeds. If it ends with an error, the caller is supposed to perform the copying manually. The dm-kcopyd subsystem is modified to use the XCOPY command, so device mapper targets that use it (mirror, snapshot, thin, cache) take advantage of copy offload automatically. There is a new ioctl BLKCOPY that makes it possible to use copy offload from userspace. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
