On 27/01/2021 15:00, Kanchan Joshi wrote: > This RFC patchset adds asynchronous ioctl capability for NVMe devices. > Purpose of RFC is to get the feedback and optimize the path. > > At the uppermost io-uring layer, a new opcode IORING_OP_IOCTL_PT is > presented to user-space applications. Like regular-ioctl, it takes > ioctl opcode and an optional argument (ioctl-specific input/output > parameter). Unlike regular-ioctl, it is made to skip the block-layer > and reach directly to the underlying driver (nvme in the case of this > patchset). This path between io-uring and nvme is via a newly > introduced block-device operation "async_ioctl". This operation > expects io-uring to supply a callback function which can be used to > report completion at later stage. > > For a regular ioctl, NVMe driver submits the command to the device and > the submitter (task) is made to wait until completion arrives. For > async-ioctl, completion is decoupled from submission. Submitter goes > back to its business without waiting for nvme-completion. When > nvme-completion arrives, it informs io-uring via the registered > completion-handler. But some ioctls may require updating certain > ioctl-specific fields which can be accessed only in context of the > submitter task. For that reason, NVMe driver uses task-work infra for > that ioctl-specific update. Since task-work is not exported, it cannot > be referenced when nvme is compiled as a module. Therefore, one of the > patch exports task-work API. > > Here goes example of usage (pseudo-code). > Actual nvme-cli source, modified to issue all ioctls via this opcode > is present at- > https://github.com/joshkan/nvme-cli/commit/a008a733f24ab5593e7874cfbc69ee04e88068c5 see https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-fops Looks like good time to bring that branch/discussion back > > With regular ioctl- > int nvme_submit_passthru(int fd, unsigned long ioctl_cmd, > struct nvme_passthru_cmd *cmd) > { > return ioctl(fd, ioctl_cmd, cmd); > } > > With uring passthru ioctl- > int nvme_submit_passthru(int fd, unsigned long ioctl_cmd, > struct nvme_passthru_cmd *cmd) > { > return uring_ioctl(fd, ioctl_cmd, cmd); > } > int uring_ioctl(int fd, unsinged long cmd, u64 arg) > { > sqe = io_uring_get_sqe(ring); > > /* prepare sqe */ > sqe->fd = fd; > sqe->opcode = IORING_OP_IOCTL_PT; > sqe->ioctl_cmd = cmd; > sqe->ioctl_arg = arg; > > /* submit sqe */ > io_uring_submit(ring); > > /* reap completion and obtain result */ > io_uring_wait_cqe(ring, &cqe); > printf("ioctl result =%d\n", cqe->res) > } > > Kanchan Joshi (4): > block: introduce async ioctl operation > kernel: export task_work_add > nvme: add async ioctl support > io_uring: add async passthrough ioctl support > > drivers/nvme/host/core.c | 347 +++++++++++++++++++++++++++------- > fs/io_uring.c | 77 ++++++++ > include/linux/blkdev.h | 12 ++ > include/uapi/linux/io_uring.h | 7 +- > kernel/task_work.c | 2 +- > 5 files changed, 376 insertions(+), 69 deletions(-) > -- Pavel Begunkov
