NAME
read, readv - read input

SYNOPSIS
cc = read(d, buf, nbytes)
int cc, d;
void *buf;
size_t nbytes;

#include <sys/types.h>
#include <sys/uio.h>

cc = readv(d, iov, iovcnt)
int cc, d;
struct iovec *iov;
int iovcnt;

DESCRIPTION
Read attempts to read nbytes of data from the object referenced by
the descriptor d into the buffer pointed to by buf. Readv performs
the same action, but scatters the input data into the iovcnt
buffers specified by the members of the iov array: iov[0], iov[1],
..., iov[iovcnt-1].

For readv, the iovec structure is defined as

struct iovec {
caddr_t iov_base;
int iov_len;
};

Each iovec entry specifies the base address and length of an area
in memory where data should be placed. Readv will always fill an
area completely before proceeding to the next.

On objects capable of seeking, the read starts at a position given
by the pointer associated with d (see lseek(2)). Upon return from
read, the pointer is incremented by the number of bytes actually
read.

Objects that are not capable of seeking always read from the
current position. The value of the pointer associated with such an
object is undefined.

Upon successful completion, read and readv return the number of
bytes actually read and placed in the buffer. The system
guarantees to read the number of bytes requested if the descriptor
references a normal file that has that many bytes left before the
end-of-file, but in no other case.

If the returned value is 0, then end-of-file has been reached.

RETURN VALUE
If successful, the number of bytes actually read is returned.
Otherwise, a -1 is returned and the global variable errno is set to
indicate the error.

ERRORS
Read and readv will fail if one or more of the following are true:

[EBADF] D is not a valid file or socket descriptor open for
reading.

[EFAULT] Buf points outside the allocated address space.

[EIO] An I/O error occurred while reading from the file
system.

[EINTR] A read from a slow device was interrupted before any
data arrived by the delivery of a signal.

[EINVAL] The pointer associated with d was negative.

[EWOULDBLOCK] The file was marked for non-blocking I/O, and no
data were ready to be read.

In addition, readv may return one of the following errors:

[EINVAL] Iovcnt was less than or equal to 0, or greater than
16.

[EINVAL] One of the iov_len values in the iov array was
negative.

[EINVAL] The sum of the iov_len values in the iov array
overflowed a 32-bit integer.

[EFAULT] Part of the iov points outside the process’s
allocated address space.

SEE ALSO
dup(2), fcntl(2), open(2), pipe(2), select(2), socket(2),
socketpair(2)