redhat man page for writev

READV(2)						     Linux Programmer's Manual							  READV(2)

NAME
       readv, writev - read or write a vector

SYNOPSIS
       #include <sys/uio.h>

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

       struct iovec {
	   void *iov_base;    /* Starting address */
	   size_t iov_len;    /* Length in bytes  */
       };

DESCRIPTION
       readv  reads  data  from  file descriptor fd, and puts the result in the buffers described by vector. The number of buffers is specified by
       count. The buffers are filled in the order specified.  Operates just like read except that data is put in vector instead  of  a	contiguous
       buffer.

       writev  writes  data to file descriptor fd, and from the buffers described by vector. The number of buffers is specified by count. The buf-
       fers are used in the order specified.  Operates just like write except that data is taken from vector instead of a contiguous buffer.

RETURN VALUE
       On success readv returns the number of bytes read.  On success writev returns the number of bytes written.  On error, -1 is  returned,  and
       errno is set appropriately.

ERRORS
       EINVAL An  invalid argument was given. For instance count might be greater than MAX_IOVEC, or zero.  fd could also be attached to an object
	      which  is  unsuitable for reading (for readv) or writing (for writev).

       EFAULT "Segmentation fault." Most likely vector or some of the iov_base pointers points to memory that is not properly allocated.

       EBADF  The file descriptor fd is not valid.

       EINTR  The call was interrupted by a signal before any data was read/written.

       EAGAIN Non-blocking I/O has been selected using O_NONBLOCK and no data was immediately available for reading.  (Or the file  descriptor	fd
	      is for an object that is locked.)

       EISDIR fd refers to a directory.

       EOPNOTSUPP
	      fd refers to a socket or device that does not support reading/writing.

       ENOMEM Insufficient kernel memory was available.

       Other errors may occur, depending on the object connected to fd.

CONFORMING TO
       4.4BSD (the readv and writev functions first appeared in BSD 4.2), Unix98.  Linux libc5 used size_t as the type of the count parameter.

SEE ALSO
       read(2), write(2), fprintf(3), fscanf(3)

Linux 2.2.0-pre8						    1999-01-20								  READV(2)