Technical Reference: Kernel and Subsystems, Volume 1

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

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

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.

Related Information

The uiomove kernel service, uphysio kernel service, uwritec kernel service.

The uio structure.

Memory Kernel Services in AIX 5L Version 5.2 Kernel Extensions and Device Support Programming Concepts.