NAME

sys/uio.h - definitions for vector I/O operations

SYNOPSIS

^[XSI] #include <sys/uio.h>

DESCRIPTION

The <sys/uio.h> header shall define the iovec structure that includes at least the following members:

void   *iov_base  Base address of a memory region for input or output. 
size_t  iov_len   The size of the memory pointed to by iov_base. 

The <sys/uio.h> header uses the iovec structure for scatter/gather I/O.

The ssize_t and size_t types shall be defined as described in <sys/types.h>.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

ssize_t readv(int, const struct iovec *, int);
ssize_t writev(int, const struct iovec *, int);

APPLICATION USAGE

The implementation can put a limit on the number of scatter/gather elements which can be processed in one call. The symbol {IOV_MAX} defined in <limits.h> should always be used to learn about the limits instead of assuming a fixed value.

RATIONALE

Traditionally, the maximum number of scatter/gather elements the system can process in one call were described by the symbolic value {UIO_MAXIOV}. In IEEE Std 1003.1-2001 this value is replaced by the constant {IOV_MAX} which can be found in <limits.h>.

FUTURE DIRECTIONS

None.

SEE ALSO

<limits.h>, <sys/types.h>, the System Interfaces volume of IEEE Std 1003.1-2001, read(), write()

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 6

Text referring to scatter/gather I/O is added to the DESCRIPTION.