blk_rq_map_user
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## Name

blk_rq_map_user — map user data to a request, for REQ_BLOCK_PC usage

## Synopsis

`int blk_rq_map_user (` | struct request_queue * | q,
| struct request * | rq,
| void __user * | ubuf,
| unsigned long | len`)`;

## Arguments

`q`

  request queue where request should be inserted

`rq`

  request structure to fill

`ubuf`

  the user buffer

`len`

  length of user data

## Description

Data will be mapped directly for zero copy io, if possible. Otherwise a kernel bounce buffer is used.

A matching `blk_rq_unmap_user` must be issued at the end of io, while still in process context.

## Note

The mapped bio may need to be bounced through `blk_queue_bounce` before being submitted to the device, as pages mapped may be out of reach. It's the callers responsibility to make sure this happens. The original bio must be passed back in to `blk_rq_unmap_user` for proper unmapping.

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