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.
todo: implement .mmap() for mapping io request pages into userspace, so
that big chunk IO zero copy can be supported
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
drivers/block/ublk_drv.c | 151 ++++++++++++++++++++++++++++++++++
include/uapi/linux/ublk_cmd.h | 22 ++++-
2 files changed, 172 insertions(+), 1 deletion(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 7f75355687fa..ebe37bb23ec6 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -206,6 +206,23 @@ static unsigned int ublks_added; /* protected by ublk_ctl_mutex */
static struct miscdevice ublk_misc;
+static inline unsigned ublk_pos_to_hwq(loff_t pos)
+{
+ return ((pos - UBLKSRV_IO_BUF_OFFSET) >> UBLK_QID_OFF) &
+ UBLK_QID_BITS_MASK;
+}
+
+static inline unsigned ublk_pos_to_buf_off(loff_t pos)
+{
+ return (pos - UBLKSRV_IO_BUF_OFFSET) & UBLK_IO_BUF_BITS_MASK;
+}
+
+static inline unsigned ublk_pos_to_tag(loff_t pos)
+{
+ return ((pos - UBLKSRV_IO_BUF_OFFSET) >> UBLK_TAG_OFF) &
+ UBLK_TAG_BITS_MASK;
+}
+
static void ublk_dev_param_basic_apply(struct ublk_device *ub)
{
struct request_queue *q = ub->ub_disk->queue;
@@ -1411,6 +1428,36 @@ static int __ublk_ch_uring_cmd(struct io_uring_cmd *cmd,
return -EIOCBQUEUED;
}
+static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
+ struct ublk_queue *ubq, int tag, size_t offset)
+{
+ struct request *req;
+
+ if (!ublk_need_req_ref(ubq))
+ return NULL;
+
+ req = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], tag);
+ if (!req)
+ return NULL;
+
+ if (!ublk_get_req_ref(ubq, req))
+ return NULL;
+
+ if (unlikely(!blk_mq_request_started(req) || req->tag != tag))
+ goto fail_put;
+
+ if (!ublk_rq_has_data(req))
+ goto fail_put;
+
+ if (offset > blk_rq_bytes(req))
+ goto fail_put;
+
+ return req;
+fail_put:
+ ublk_put_req_ref(ubq, req);
+ return NULL;
+}
+
static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
{
struct ublksrv_io_cmd *ub_src = (struct ublksrv_io_cmd *) cmd->cmd;
@@ -1428,11 +1475,112 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
return __ublk_ch_uring_cmd(cmd, issue_flags, &ub_cmd);
}
+static inline bool ublk_check_ubuf_dir(const struct request *req,
+ int ubuf_dir)
+{
+ /* copy ubuf to request pages */
+ if (req_op(req) == REQ_OP_READ && ubuf_dir == ITER_SOURCE)
+ return true;
+
+ /* copy request pages to ubuf */
+ if (req_op(req) == REQ_OP_WRITE && ubuf_dir == ITER_DEST)
+ return true;
+
+ return false;
+}
+
+static struct request *ublk_check_and_get_req(struct kiocb *iocb,
+ struct iov_iter *iter, size_t *off, int dir)
+{
+ struct ublk_device *ub = iocb->ki_filp->private_data;
+ struct ublk_queue *ubq;
+ struct request *req;
+ size_t buf_off;
+ u16 tag, q_id;
+
+ if (!ub)
+ return ERR_PTR(-EACCES);
+
+ if (!user_backed_iter(iter))
+ return ERR_PTR(-EACCES);
+
+ if (ub->dev_info.state == UBLK_S_DEV_DEAD)
+ return ERR_PTR(-EACCES);
+
+ tag = ublk_pos_to_tag(iocb->ki_pos);
+ q_id = ublk_pos_to_hwq(iocb->ki_pos);
+ buf_off = ublk_pos_to_buf_off(iocb->ki_pos);
+
+ if (q_id >= ub->dev_info.nr_hw_queues)
+ return ERR_PTR(-EINVAL);
+
+ ubq = ublk_get_queue(ub, q_id);
+ if (!ubq)
+ return ERR_PTR(-EINVAL);
+
+ if (tag >= ubq->q_depth)
+ return ERR_PTR(-EINVAL);
+
+ req = __ublk_check_and_get_req(ub, ubq, tag, buf_off);
+ if (!req)
+ return ERR_PTR(-EINVAL);
+
+ if (!req->mq_hctx || !req->mq_hctx->driver_data)
+ goto fail;
+
+ if (!ublk_check_ubuf_dir(req, dir))
+ goto fail;
+
+ *off = buf_off;
+ return req;
+fail:
+ ublk_put_req_ref(ubq, req);
+ return ERR_PTR(-EACCES);
+}
+
+static ssize_t ublk_ch_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+ struct ublk_queue *ubq;
+ struct request *req;
+ size_t buf_off;
+ size_t ret;
+
+ req = ublk_check_and_get_req(iocb, to, &buf_off, ITER_DEST);
+ if (IS_ERR(req))
+ return PTR_ERR(req);
+
+ ret = ublk_copy_user_pages(req, buf_off, to, ITER_DEST);
+ ubq = req->mq_hctx->driver_data;
+ ublk_put_req_ref(ubq, req);
+
+ return ret;
+}
+
+static ssize_t ublk_ch_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+ struct ublk_queue *ubq;
+ struct request *req;
+ size_t buf_off;
+ size_t ret;
+
+ req = ublk_check_and_get_req(iocb, from, &buf_off, ITER_SOURCE);
+ if (IS_ERR(req))
+ return PTR_ERR(req);
+
+ ret = ublk_copy_user_pages(req, buf_off, from, ITER_SOURCE);
+ ubq = req->mq_hctx->driver_data;
+ ublk_put_req_ref(ubq, req);
+
+ return ret;
+}
+
static const struct file_operations ublk_ch_fops = {
.owner = THIS_MODULE,
.open = ublk_ch_open,
.release = ublk_ch_release,
.llseek = no_llseek,
+ .read_iter = ublk_ch_read_iter,
+ .write_iter = ublk_ch_write_iter,
.uring_cmd = ublk_ch_uring_cmd,
.mmap = ublk_ch_mmap,
};
@@ -2331,6 +2479,9 @@ static int __init ublk_init(void)
{
int ret;
+ BUILD_BUG_ON((unsigned long long)UBLKSRV_IO_BUF_OFFSET +
+ UBLKSRV_IO_BUF_BITS_SIZE < UBLKSRV_IO_BUF_OFFSET);
+
init_waitqueue_head(&ublk_idr_wq);
ret = misc_register(&ublk_misc);
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 640bf687b94a..a20ea079ca9b 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -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 15bit, 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 32K IOs for each queue */
+#define UBLK_TAG_OFF UBLK_IO_BUF_BITS
+#define UBLK_TAG_BITS 15
+#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_BITS (UBLK_QID_OFF + UBLK_QID_BITS)
+#define UBLKSRV_IO_BUF_BITS_SIZE (1ULL << UBLKSRV_IO_BUF_BITS)
+
/*
* zero copy requires 4k block size, and can remap ublk driver's io
* request into ublksrv's vm space
--
2.40.0
