READV (2)
read or write a vector
SYNOPSIS
#include <sys/uio.h>
int readv(int fd , const struct iovec * vector , int count );
int writev(int fd , const struct iovec * vector , int count );
struct iovec {
__ptr_t 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 buffers 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.
EOPNOTSUP
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 uses
size_t as the type of the count parameter, which is
logical but non-standard.
SEE ALSO
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