March 7, 2007 UIOMOVE 9

### NAME

uiomove - move data described by a struct uio

### SYNOPSIS

```int` uiomove(```void *buf``, size_t n``, struct uio *uio`)

### DESCRIPTION

The uiomove function copies up to ```n` bytes between the kernel-space address pointed to by ```buf` and the addresses described by ```uio`, which may be in user-space or kernel-space.

The ```uio` argument is a pointer to a ```struct` `uio` as defined by <```sys/uio.h`>: ``

    struct uio {
            struct  iovec *uio_iov; /* pointer to array of iovecs */
            int     uio_iovcnt;     /* number of iovecs in array */
            off_t   uio_offset;     /* offset into file this uio corresponds to */
            size_t  uio_resid;      /* residual i/o count */
            enum    uio_rw uio_rw;
            struct  vmspace *uio_vmspace;
    };

A ```struct` `uio` typically describes data in motion. Several of the fields described below reflect that expectation.

uio_iov
  Pointer to array of ```struct` `iovecs`: `

      struct iovec {
              void    *iov_base;      /* Base address. */
              size_t   iov_len;       /* Length. */
      };

  `

uio_iovcnt
  The number of iovecs in the array.

uio_offset
  An offset into the corresponding object.

uio_resid
  The amount of space described by the structure; notionally, the amount of data remaining to be transferred.

uio_rw
  A flag indicating whether data should be read into the space (UIO_READ) or written from the space (UIO_WRITE).

uio_vmspace
  A pointer to the address space which is being transferred to or from.

The value of ```uio->uio_rw` controls whether uiomove copies data from ```buf` to ```uio` or vice versa.

The lesser of ```n` or ```uio->uio_resid` bytes are copied.

uiomove changes fields of the structure pointed to by ```uio`, such that ```uio->uio_resid` is decremented by the amount of data moved, ```uio->uio_offset` is incremented by the same amount, and the array of iovecs is adjusted to point that much farther into the region described. This allows multiple calls to uiomove to easily be used to fill or drain the region of data.

### RETURN VALUES

uiomove returns 0 on success or EFAULT if a bad address is encountered.

### SEE ALSO

copy(9), fetch(9), store(9)