Commit 71f28f31 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe

ublk_drv: add io_uring based userspace block driver

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 is small/simple enough.

[1] ublksrv

https://github.com/ming1/ubdsrvSigned-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220713140711.97356-2-ming.lei@redhat.comSigned-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 96388f57
......@@ -408,6 +408,15 @@ config BLK_DEV_RBD
If unsure, say N.
config BLK_DEV_UBLK
tristate "Userspace block driver (Experimental)"
select IO_URING
help
io_uring based userspace block driver. Together with ublk server, ublk
has been working well, but interface with userspace or command data
definition isn't finalized yet, and might change according to future
requirement, so mark is as experimental now.
source "drivers/block/rnbd/Kconfig"
endif # BLK_DEV
......@@ -39,4 +39,6 @@ obj-$(CONFIG_BLK_DEV_RNBD) += rnbd/
obj-$(CONFIG_BLK_DEV_NULL_BLK) += null_blk/
obj-$(CONFIG_BLK_DEV_UBLK) += ublk_drv.o
swim_mod-y := swim.o swim_asm.o
This diff is collapsed.
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
#ifndef USER_BLK_DRV_CMD_INC_H
#define USER_BLK_DRV_CMD_INC_H
#include <linux/types.h>
/* ublk server command definition */
/*
* Admin commands, issued by ublk server, and handled by ublk driver.
*/
#define UBLK_CMD_GET_QUEUE_AFFINITY 0x01
#define UBLK_CMD_GET_DEV_INFO 0x02
#define UBLK_CMD_ADD_DEV 0x04
#define UBLK_CMD_DEL_DEV 0x05
#define UBLK_CMD_START_DEV 0x06
#define UBLK_CMD_STOP_DEV 0x07
/*
* IO commands, issued by ublk server, and handled by ublk driver.
*
* FETCH_REQ: issued via sqe(URING_CMD) beforehand for fetching IO request
* from ublk driver, should be issued only when starting device. After
* the associated cqe is returned, request's tag can be retrieved via
* cqe->userdata.
*
* COMMIT_AND_FETCH_REQ: issued via sqe(URING_CMD) after ublkserver handled
* this IO request, request's handling result is committed to ublk
* driver, meantime FETCH_REQ is piggyback, and FETCH_REQ has to be
* handled before completing io request.
*/
#define UBLK_IO_FETCH_REQ 0x20
#define UBLK_IO_COMMIT_AND_FETCH_REQ 0x21
/* only ABORT means that no re-fetch */
#define UBLK_IO_RES_OK 0
#define UBLK_IO_RES_ABORT (-ENODEV)
#define UBLKSRV_CMD_BUF_OFFSET 0
#define UBLKSRV_IO_BUF_OFFSET 0x80000000
/* tag bit is 12bit, so at most 4096 IOs for each queue */
#define UBLK_MAX_QUEUE_DEPTH 4096
/*
* zero copy requires 4k block size, and can remap ublk driver's io
* request into ublksrv's vm space
*/
#define UBLK_F_SUPPORT_ZERO_COPY (1UL << 0)
/* device state */
#define UBLK_S_DEV_DEAD 0
#define UBLK_S_DEV_LIVE 1
/* shipped via sqe->cmd of io_uring command */
struct ublksrv_ctrl_cmd {
/* sent to which device, must be valid */
__u32 dev_id;
/* sent to which queue, must be -1 if the cmd isn't for queue */
__u16 queue_id;
/*
* cmd specific buffer, can be IN or OUT.
*/
__u16 len;
__u64 addr;
/* inline data */
__u64 data[2];
};
struct ublksrv_ctrl_dev_info {
__u16 nr_hw_queues;
__u16 queue_depth;
__u16 block_size;
__u16 state;
__u32 rq_max_blocks;
__u32 dev_id;
__u64 dev_blocks;
__s32 ublksrv_pid;
__s32 reserved0;
__u64 flags[2];
/* For ublksrv internal use, invisible to ublk driver */
__u64 ublksrv_flags;
__u64 reserved1[9];
};
#define UBLK_IO_OP_READ 0
#define UBLK_IO_OP_WRITE 1
#define UBLK_IO_OP_FLUSH 2
#define UBLK_IO_OP_DISCARD 3
#define UBLK_IO_OP_WRITE_SAME 4
#define UBLK_IO_OP_WRITE_ZEROES 5
#define UBLK_IO_F_FAILFAST_DEV (1U << 8)
#define UBLK_IO_F_FAILFAST_TRANSPORT (1U << 9)
#define UBLK_IO_F_FAILFAST_DRIVER (1U << 10)
#define UBLK_IO_F_META (1U << 11)
#define UBLK_IO_F_INTEGRITY (1U << 12)
#define UBLK_IO_F_FUA (1U << 13)
#define UBLK_IO_F_PREFLUSH (1U << 14)
#define UBLK_IO_F_NOUNMAP (1U << 15)
#define UBLK_IO_F_SWAP (1U << 16)
/*
* io cmd is described by this structure, and stored in share memory, indexed
* by request tag.
*
* The data is stored by ublk driver, and read by ublksrv after one fetch command
* returns.
*/
struct ublksrv_io_desc {
/* op: bit 0-7, flags: bit 8-31 */
__u32 op_flags;
__u32 nr_sectors;
/* start sector for this io */
__u64 start_sector;
/* buffer address in ublksrv daemon vm space, from ublk driver */
__u64 addr;
};
static inline __u8 ublksrv_get_op(const struct ublksrv_io_desc *iod)
{
return iod->op_flags & 0xff;
}
static inline __u32 ublksrv_get_flags(const struct ublksrv_io_desc *iod)
{
return iod->op_flags >> 8;
}
/* issued to ublk driver via /dev/ublkcN */
struct ublksrv_io_cmd {
__u16 q_id;
/* for fetch/commit which result */
__u16 tag;
/* io result, it is valid for COMMIT* command only */
__s32 result;
/*
* userspace buffer address in ublksrv daemon process, valid for
* FETCH* command only
*/
__u64 addr;
};
#endif
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