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ublk: add read()/write() support for ublk char device

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Support pread()/pwrite() on ublk char device for reading/writing request
io buffer, so data copy between io request buffer and userspace buffer
can be moved to ublk server from ublk driver. Then UBLK_F_NEED_GET_DATA
becomes not necessary, so ublk server can allocate buffer without one
extra round uring command communication for userspace to provide buffer.

IO buffer can be located by iocb->ki_pos which encodes buffer offset, io
tag and queue id info, and type of iocb->ki_pos is u64, so it is big
enough for holding reasonable queue depth, nr_queues and max io buffer
size.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei
2023-05-19 14:50:29 +08:00
committed by Jens Axboe
parent 38f2dd3441
commit 62fe99cef9
2 changed files with 172 additions and 1 deletions
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22
include/uapi/linux/ublk_cmd.h
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@@ -93,9 +93,29 @@
#define UBLKSRV_CMD_BUF_OFFSET 0
#define UBLKSRV_IO_BUF_OFFSET 0x80000000
/* tag bit is 12bit, so at most 4096 IOs for each queue */
/* tag bit is 16bit, so far limit at most 4096 IOs for each queue */
#define UBLK_MAX_QUEUE_DEPTH 4096
/* single IO buffer max size is 32MB */
#define UBLK_IO_BUF_OFF 0
#define UBLK_IO_BUF_BITS 25
#define UBLK_IO_BUF_BITS_MASK ((1ULL << UBLK_IO_BUF_BITS) - 1)
/* so at most 64K IOs for each queue */
#define UBLK_TAG_OFF UBLK_IO_BUF_BITS
#define UBLK_TAG_BITS 16
#define UBLK_TAG_BITS_MASK ((1ULL << UBLK_TAG_BITS) - 1)
/* max 4096 queues */
#define UBLK_QID_OFF (UBLK_TAG_OFF + UBLK_TAG_BITS)
#define UBLK_QID_BITS 12
#define UBLK_QID_BITS_MASK ((1ULL << UBLK_QID_BITS) - 1)
#define UBLK_MAX_NR_QUEUES (1U << UBLK_QID_BITS)
#define UBLKSRV_IO_BUF_TOTAL_BITS (UBLK_QID_OFF + UBLK_QID_BITS)
#define UBLKSRV_IO_BUF_TOTAL_SIZE (1ULL << UBLKSRV_IO_BUF_TOTAL_BITS)
/*
* zero copy requires 4k block size, and can remap ublk driver's io
* request into ublksrv's vm space