---
title: physio
framework: Kernel
role: symbol
role_heading: Function
platforms: [macOS 10.4+]
path: kernel/1561895-physio
---

# physio

Perform I/O on a device to/from target memory described by a uio.

## Declaration

```occ
int physio(void (*f_strategy)(buf_t), buf_t bp, dev_t dev, int flags, u_int (*f_minphys)(buf_t), struct uio *uio, int blocksize);
```

## Parameters

- `f_strategy`: Strategy routine to call to initiate I/O.
- `bp`: Buffer to configure and pass to strategy routine; can be NULL.
- `dev`: Device on which to perform I/O.
- `flags`: B_READ or B_WRITE.
- `f_minphys`: Function which calls buf_setcount() to set a byte count which is suitably small for the device in question. Returns byte count that has been set (or unchanged) on the buffer.
- `uio`: UIO describing the I/O operation.
- `blocksize`: Logical block size for this vnode.

## Return Value

Return Value 0 for success; EFAULT for an invalid uio; errors from buf_biowait().

## Discussion

Discussion physio() allows I/O directly from a device to user-space memory. It waits for all I/O to complete before returning.