subyte Kernel Service

Purpose

Stores a byte of data in user memory.

Syntax

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

int subyte ( uaddr,  c)
uchar *uaddr;
uchar c;

Parameters

Item Description
uaddr Specifies the address of user data.
c Specifies the character to store.

Description

The subyte kernel service stores a byte of data at the specified address in user memory. It is provided so that system calls and device heads can safely access user data. The subyte service ensures that the user has the appropriate authority to:

The subyte service should only be called while executing in kernel mode in the user process.

Execution Environment

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

Return Values

Item Description
0 Indicates successful completion.
-1 Indicates a uaddr parameter that is not valid for one of the following reasons:
  • The user does not have sufficient authority to access the data.
  • The address is not valid.
  • An I/O error occurs when the user data is referenced.