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AIX Version 4.3 Kernel and Subsystems Technical Reference, Volume 1

subyte Kernel Service


Stores a byte of data in user memory.


#include <sys/types.h>
#include <sys/errno.h>
int subyte (uaddr, c)
uchar *uaddr;
uchar c;


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


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

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.

Implementation Specifics

The subyte kernel service is part of Base Operating System (BOS) Runtime.

Related Information

The fubyte kernel service, fuword kernel service, suword kernel service.

Accessing User-Mode Data While in Kernel Mode and Memory Kernel Services in AIX Kernel Extensions and Device Support Programming Concepts.

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