On Mon, Jul 04, 2022 at 02:17:44PM +0300, Sagi Grimberg wrote: > > > This is the driver part of userspace block driver(ublk driver), the other > > part is userspace daemon part(ublksrv)[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 > > ublksrv, each io command is indexed by io request tag directly, and > > is written by ublk driver. > > > > For example, when one READ io request is submitted to ublk block driver, ublk > > driver stores the io command into cmd buffer first, then completes one > > IORING_OP_URING_CMD for notifying ublksrv, and the URING_CMD is issued to > > ublk driver beforehand by ublksrv for getting notification of any new io request, > > and each URING_CMD is associated with one io request by tag. > > > > After ublksrv gets the io command, it translates and handles the ublk io > > request, such as, for the ublk-loop target, ublksrv translates the request > > into same request on another file or disk, like the kernel loop block > > driver. In ublksrv'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 ublk driver for > > both committing io request result and getting future notification of new > > io request. > > > > Another thing done by ublk driver is to copy data between kernel io > > request and ublksrv's io buffer: > > > > 1) before ubsrv handles WRITE request, copy the request's data into > > ublksrv's userspace io buffer, so that ublksrv can handle the write > > request > > > > 2) after ubsrv handles READ request, copy ublksrv's userspace io buffer > > into this READ request, then ublk driver can complete the READ request > > > > Zero copy may be switched if mm is ready to support it. > > > > ublk driver doesn't handle any logic of the specific user space driver, > > so it should be small/simple enough. > > > > [1] ublksrv > > > > https://github.com/ming1/ubdsrv > > > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > > --- > > drivers/block/Kconfig | 6 + > > drivers/block/Makefile | 2 + > > drivers/block/ublk_drv.c | 1603 +++++++++++++++++++++++++++++++++ > > include/uapi/linux/ublk_cmd.h | 158 ++++ > > 4 files changed, 1769 insertions(+) > > create mode 100644 drivers/block/ublk_drv.c > > create mode 100644 include/uapi/linux/ublk_cmd.h > > > > diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig > > index fdb81f2794cd..d218089cdbec 100644 > > --- a/drivers/block/Kconfig > > +++ b/drivers/block/Kconfig > > @@ -408,6 +408,12 @@ config BLK_DEV_RBD > > If unsure, say N. > > +config BLK_DEV_UBLK > > + bool "Userspace block driver" > > Really? why compile this to the kernel and not tristate as loadable > module? So far, this is only one reason: task_work_add() is required, which isn't exported for modules. Thanks, Ming
