uiomove - General: Moves data between user and system virtual
space
#include <sys/uio.h>
int uiomove(
caddr_t kern_buf,
int nbytes,
struct uio *uio );
Specifies a pointer to the kernel buffer in system virtual
space. Specifies the number of bytes of data to be moved.
Specifies a pointer to a uio structure. This structure
describes the current position within a logical user
buffer in user virtual space.
The uiomove routine moves data between user and system
virtual space. Data can be moved in either direction.
Accessibility to the logical user buffer is verified
before the move is made. Accessibility to the kernel
buffer is always assumed.
The kernel buffer must always be of sufficient size to
accommodate the data. It cannot be less than the number of
bytes requested to be moved. Data corruption or a system
panic may result if this condition occurs.
The size of the logical user buffer, as described by the
uio structure, may be less than, equal to, or greater than
the number of bytes requested. The number of bytes actually
moved is truncated whenever this size is not sufficient
to fulfill a request. In all other cases, only the
bytes requested are moved.
Normally there is no need for kernel modules to set up uio
structures or worry about their composition or content.
The uio structures are usually set up externally to kernel
modules. Their addresses are passed in through the dsent
table as arguments to module read and write routines. The
user logical buffers they describe are accessed only by
routines external to the module, for example, uiomove. The
external uio structures are quite often updated by such
accesses.
The uiomove routine always updates the uio structure to
reflect the number of bytes actually moved. The structure
continues to describe the current position within the logical
user buffer. The structure members that are subject
to change are listed in the SIDE EFFECTS section.
You can also use the uiomove routine to move data only
within system virtual space. In such cases, you still
specify a pointer to a uio structure. However, in these
cases, the structure describes a logical buffer in system
virtual space.
The uiomove routine can update the following members of
the uio structure: Specifies the address of the current
logical buffer segment. Specifies the number of remaining
logical buffer segments. Specifies the size of the
remaining logical buffer. Specifies the current offset
into the full logical buffer.
The uiomove routine can update the following members of
uio_iov (the logical buffer segment descriptor vector):
Specifies the address of the current byte within the current
logical buffer segment. Specifies the remaining size
of the current segment.
Upon successfully moving the data, the uiomove routine
returns the value 0 (zero). This action implies that the
user virtual space described by the uio structure is
accessible. Otherwise, uiomove returns the error value
EFAULT, indicating an inability to fully access the user
virtual space from within the context of the current process.
A partial move may have occurred before the logical
user buffer became inaccessible. The uio structure is
appropriately updated to reflect such partial moves.
The EFAULT return value is suitable for placement in the
u_error member of the user structure. Following failure of
a system call, this member contains the error code automatically
returned in errno to the current process. Kernel
module writers should explicitly set this value when
it is returned and disallow the requested operation. This
setting lets the current process determine the appropriate
reason (``bad address'') why its request could not be satisfied.
Routines: copyin(9r), copyout(9r), fubyte(9r), subyte(9r)
Data Structures: uio(9s)
uiomove(9r)
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