On 09.05.2022 11:23 Ming Lei wrote: > This is the driver part of userspace block driver(ubd driver), the other > part is userspace daemon part(ubdsrv)[1]. > > The two parts communicate by io_uring's IORING_OP_URING_CMD with one > shared cmd buffer for storing io command, and the buffer is read only for > ubdsrv, each io command is indexed by io request tag directly, and > is written by ubd driver. > > For example, when one READ io request is submitted to ubd block driver, ubd > driver stores the io command into cmd buffer first, then completes one > IORING_OP_URING_CMD for notifying ubdsrv, and the URING_CMD is issued to > ubd driver beforehand by ubdsrv for getting notification of any new io request, > and each URING_CMD is associated with one io request by tag. > > After ubdsrv gets the io command, it translates and handles the ubd io > request, such as, for the ubd-loop target, ubdsrv translates the request > into same request on another file or disk, like the kernel loop block > driver. In ubdsrv's implementation, the io is still handled by io_uring, > and share same ring with IORING_OP_URING_CMD command. When the target io > request is done, the same IORING_OP_URING_CMD is issued to ubd driver for > both committing io request result and getting future notification of new > io request. > > Another thing done by ubd driver is to copy data between kernel io > request and ubdsrv's io buffer: > > 1) before ubsrv handles WRITE request, copy the request's data into > ubdsrv's userspace io buffer, so that ubdsrv can handle the write > request > > 2) after ubsrv handles READ request, copy ubdsrv's userspace io buffer > into this READ request, then ubd driver can complete the READ request > > Zero copy may be switched if mm is ready to support it. > > ubd driver doesn't handle any logic of the specific user space driver, > so it should be small/simple enough. > > [1] ubdsrv > https://github.com/ming1/ubdsrv/commits/devel Great! It would be interesting to do some tests on how much faster (IOPS) this is than doing this via fuse: https://github.com/uroni/fuseuring
