ureadc Kernel Service

Purpose

Writes a character to a buffer described by a uio structure.

Syntax

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/uio.h>

int ureadc ( c, uiop) int c; struct uio *uiop;

Parameters

Item	Description
c	Specifies a character to be written to the buffer.
uiop	Points to a uio structure describing the buffer in which to place a character.

Description

The ureadc kernel service writes a character to a buffer described by a uio structure. Device driver top half routines, especially character device drivers, frequently use the ureadc kernel service to transfer data into a user area.

The uio_resid and uio_iovcnt fields in the uio structure describing the data area must be greater than 0. If these fields are not greater than 0, an error is returned. The uio_segflg field in the uio structure is used to indicate whether the data is being written to a user- or kernel-data area. It is also used to indicate if the caller requires cross-memory operations and has provided the required cross-memory descriptors. The values for the flag are defined in the /usr/include/sys/uio.h file.

If the data is successfully written, the following fields in the uio structure are updated:

Field	Description
`uio_iov`	Specifies the address of current `iovec` element to use.
`uio_xmem`	Specifies the address of current `xmem` element to use (used for cross-memory copy).
`uio_iovcnt`	Specifies the number of remaining `iovec` elements.
`uio_iovdcnt`	Specifies the number of `iovec` elements already processed.
`uio_offset`	Specifies the character offset on the device from which data is read.
`uio_resid`	Specifies the total number of characters remaining in the data area described by the `uio` structure.
`iov_base`	Specifies the address of the next available character in the data area described by the current `iovec` element.
`iov_len`	Specifies the length of remaining data area in the buffer described by the current `iovec` element.

Execution Environment

The ureadc kernel service can be called from the process environment only.

Return Values

Item	Description
0	Indicates successful completion.
ENOMEM	Indicates that there is no room in the buffer.
EFAULT	Indicates that the user location is not valid for one of these reasons: The `uio_segflg` field indicates user space and the base address (`iov_base` field) points to a location outside of the user address space. The user does not have sufficient authority to access the location. An I/O error occurs while accessing the location.