redhat man page for readv

READV(3)						     Linux Programmer's Manual							  READV(3)

NAME
       readv, writev - read or write data into multiple buffers

SYNOPSIS
       #include <sys/uio.h>

       int readv(int filedes, const struct iovec *vector,
		 size_t count);

       int writev(int filedes, const struct iovec *vector,
		 size_t count);

DESCRIPTION
       The  readv()  function  reads count blocks from the file associated with the file descriptor filedes into the multiple buffers described by
       vector.

       The writev() function writes at most count blocks described by vector to the file associated with the file descriptor filedes.

       The pointer vector points to a struct iovec defined in <sys/uio.h> as

	  struct iovec {
	      void *iov_base;	/* Starting address */
	      size_t iov_len;	/* Number of bytes */
	  };

       Buffers are processed in the order vector[0], vector[1], ... vector[count].

       The readv() function works just like read(2) except that multiple buffers are filled.

       The writev() function works just like write(2) except that multiple buffers are written out.

RETURN VALUE
       The readv() function returns the number of bytes or -1 on error; the writev() function returns the number of bytes written.

ERRORS
       The readv() and writev() functions can fail and set errno to the following values:

       EBADF  fd is not a valid file descriptor.

       EINVAL fd is unsuitable for reading (for readv()) or writing (for writev()).

       EFAULT buf is outside the processes' address space.

       EAGAIN Non-blocking I/O had been selected in the open() call, and reading or writing could not be done immediately.

       EINTR  Reading or writing was interrupted before any data was transferred.

CONFORMING TO
       unknown

BUGS
       It is not advisable to mix calls to functions like readv() or writev(), which operate on file descriptors,  with  the  functions  from  the
       stdio library; the results will be undefined and probably not what you want.

SEE ALSO
       read(2), write(2)

GNU
								    1993-04-25								  READV(3)