On 27/01/2021 15:42, Pavel Begunkov wrote: > 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 a bit more context: https://github.com/axboe/liburing/issues/270 -- Pavel Begunkov
