Hello Jens and Guys, Add generic fused command, which can include one primary command and multiple secondary requests. This command provides one safe way to share resource between primary command and secondary requests, and primary command is always completed after all secondary requests are done, and resource lifetime is bound with primary command. With this way, it is easy to support zero copy for ublk/fuse device, and there could be more potential use cases, such as offloading complicated logic into userspace, or decouple kernel subsystems. Follows ublksrv code, which implements zero copy for loop, nbd and qcow2 targets with fused command: https://github.com/ming1/ubdsrv/tree/fused-cmd-zc-for-v6 All three(loop, nbd and qcow2) ublk targets have supported zero copy by passing: ublk add -t [loop|nbd|qcow2] -z .... Also add liburing test case for covering fused command based on miniublk of blktest. https://github.com/ming1/liburing/tree/fused_cmd_miniublk_for_v6 Performance improvement is obvious on memory bandwidth related workloads, such as, 1~2X improvement on 64K/512K BS IO test on loop with ramfs backing file. ublk-null shows 5X IOPS improvement on big BS test when the copy is avoided. Please review and consider for v6.4. V6: - re-design fused command, and make it more generic, moving sharing buffer as one plugin of fused command, so in future we can implement more plugins - document potential other use cases of fused command - drop support for builtin secondary sqe in SQE128, so all secondary requests has standalone SQE - make fused command as one feature - cleanup & improve naming V5: - rebase on for-6.4/io_uring - rename to primary/secondary as suggested by Jens - reserve interface for extending to support multiple secondary OPs in future, which isn't a must, because it can be done by submitting multiple fused commands with same primary request - rename to primary/secondary in ublksrv and liburing test code V4: - improve APIs naming(patch 1 ~ 4) - improve documents and commit log(patch 2) - add buffer direction bit to opdef, suggested by Jens(patch 2) - add ublk zero copy document for cover: technical requirements(most related with buffer lifetime), and explains why splice isn't good and how fused command solves it(patch 17) - fix sparse warning(patch 7) - supports 64byte SQE fused command(patch 3) V3: - fix build warning reported by kernel test robot - drop patch for checking fused flags on existed drivers with ->uring_command(), which isn't necessary, since we do not do that when adding new ioctl or uring command - inline io_init_rq() for core code, so just export io_init_secondary_req - return result of failed secondary request unconditionally since REQ_F_CQE_SKIP will be cleared - pass xfstest over ublk-loop V2: - don't resue io_mapped_ubuf (io_uring) - remove REQ_F_FUSED_MASTER_BIT (io_uring) - fix compile warning (io_uring) - rebase on v6.3-rc1 (io_uring) - grabbing io request reference when handling fused command - simplify ublk_copy_user_pages() by iov iterator - add read()/write() for userspace to read/write ublk io buffer, so that some corner cases(read zero, passthrough request(report zones)) can be handled easily in case of zero copy; this way also helps to switch to zero copy completely - misc cleanup Ming Lei (17): io_uring: increase io_kiocb->flags into 64bit io_uring: use ctx->cached_sq_head to calculate left sqes io_uring: add generic IORING_OP_FUSED_CMD io_uring: support providing buffer by IORING_OP_FUSED_CMD io_uring: support OP_READ/OP_WRITE for fused secondary request io_uring: support OP_SEND_ZC/OP_RECV for fused secondary request block: ublk_drv: add common exit handling block: ublk_drv: don't consider flush request in map/unmap io block: ublk_drv: add two helpers to clean up map/unmap request block: ublk_drv: clean up several helpers block: ublk_drv: cleanup 'struct ublk_map_data' block: ublk_drv: cleanup ublk_copy_user_pages block: ublk_drv: grab request reference when the request is handled by userspace block: ublk_drv: support to copy any part of request pages block: ublk_drv: add read()/write() support for ublk char device block: ublk_drv: don't check buffer in case of zero copy block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy Documentation/block/ublk.rst | 126 ++++++- drivers/block/ublk_drv.c | 603 ++++++++++++++++++++++++++------- include/linux/io_uring.h | 41 ++- include/linux/io_uring_types.h | 76 +++-- include/uapi/linux/io_uring.h | 22 +- include/uapi/linux/ublk_cmd.h | 37 +- io_uring/Makefile | 2 +- io_uring/fused_cmd.c | 239 +++++++++++++ io_uring/fused_cmd.h | 16 + io_uring/io_uring.c | 57 +++- io_uring/io_uring.h | 5 + io_uring/net.c | 30 +- io_uring/opdef.c | 22 ++ io_uring/opdef.h | 7 + io_uring/rw.c | 21 ++ 15 files changed, 1124 insertions(+), 180 deletions(-) create mode 100644 io_uring/fused_cmd.c create mode 100644 io_uring/fused_cmd.h -- 2.39.2
