AIO_READ(2)               FreeBSD System Calls Manual              AIO_READ(2)

NAME
     aio_read, aio_readv - asynchronous read from a file (REALTIME)

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <aio.h>

     int
     aio_read(struct aiocb *iocb);

     #include <sys/uio.h>

     int
     aio_readv(struct aiocb *iocb);

DESCRIPTION
     The aio_read() and aio_readv() system calls allow the calling process to
     read from the descriptor iocb->aio_fildes beginning at the offset
     iocb->aio_offset.  aio_read() will read iocb->aio_nbytes from the buffer
     pointed to by iocb->aio_buf, whereas aio_readv() reads the data into the
     iocb->aio_iovcnt buffers specified by the members of the iocb->aio_iov
     array.  Both syscalls return immediately after the read request has been
     enqueued to the descriptor; the read may or may not have completed at the
     time the call returns.

     For aio_readv() the iovec structure is defined in readv(2).

     If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then
     the enqueued operation is submitted at a priority equal to that of the
     calling process minus iocb->aio_reqprio.

     The iocb->aio_lio_opcode argument is ignored by the aio_read() and
     aio_readv() system calls.

     The iocb pointer may be subsequently used as an argument to aio_return()
     and aio_error() in order to determine return or error status for the
     enqueued operation while it is in progress.

     If the request could not be enqueued (generally due to invalid
     arguments), then the call returns without having enqueued the request.

     If the request is successfully enqueued, the value of iocb->aio_offset
     can be modified during the request as context, so this value must not be
     referenced after the request is enqueued.

     The iocb->aio_sigevent structure can be used to request notification of
     the operation's completion as described in aio(4).

RESTRICTIONS
     The Asynchronous I/O Control Block structure pointed to by iocb and the
     buffer that the iocb->aio_buf member of that structure references must
     remain valid until the operation has completed.

     The asynchronous I/O control buffer iocb should be zeroed before the
     aio_read() call to avoid passing bogus context information to the kernel.

     Modifications of the Asynchronous I/O Control Block structure or the
     buffer contents are not allowed while the request is queued.

     If the file offset in iocb->aio_offset is past the offset maximum for
     iocb->aio_fildes, no I/O will occur.

RETURN VALUES
     The aio_read() and aio_readv() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

DIAGNOSTICS
     None.

ERRORS
     The aio_read() and aio_readv() system calls will fail if:

     [EAGAIN]           The request was not queued because of system resource
                        limitations.

     [EFAULT]           Part of aio_iov points outside the process's allocated
                        address space.

     [EINVAL]           The asynchronous notification method in
                        iocb->aio_sigevent.sigev_notify is invalid or not
                        supported.

     [EOPNOTSUPP]       Asynchronous read operations on the file descriptor
                        iocb->aio_fildes are unsafe and unsafe asynchronous
                        I/O operations are disabled.

     The following conditions may be synchronously detected when the
     aio_read() or aio_readv() system call is made, or asynchronously, at any
     time thereafter.  If they are detected at call time, aio_read() or
     aio_readv() returns -1 and sets errno appropriately; otherwise the
     aio_return() system call must be called, and will return -1, and
     aio_error() must be called to determine the actual value that would have
     been returned in errno.

     [EBADF]            The iocb->aio_fildes argument is invalid.

     [EINVAL]           The offset iocb->aio_offset is not valid, the priority
                        specified by iocb->aio_reqprio is not a valid
                        priority, or the number of bytes specified by
                        iocb->aio_nbytes is not valid.

     [EOVERFLOW]        The file is a regular file, iocb->aio_nbytes is
                        greater than zero, the starting offset in
                        iocb->aio_offset is before the end of the file, but is
                        at or beyond the iocb->aio_fildes offset maximum.

     If the request is successfully enqueued, but subsequently cancelled or an
     error occurs, the value returned by the aio_return() system call is per
     the read(2) system call, and the value returned by the aio_error() system
     call is either one of the error returns from the read(2) system call, or
     one of:

     [EBADF]            The iocb->aio_fildes argument is invalid for reading.

     [ECANCELED]        The request was explicitly cancelled via a call to
                        aio_cancel().

     [EINVAL]           The offset iocb->aio_offset would be invalid.

SEE ALSO
     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
     aio_waitcomplete(2), aio_write(2), sigevent(3), siginfo(3), aio(4)

STANDARDS
     The aio_read() system call is expected to conform to the IEEE Std 1003.1
     ("POSIX.1") standard.  The aio_readv() system call is a FreeBSD
     extension, and should not be used in portable code.

HISTORY
     The aio_read() system call first appeared in FreeBSD 3.0.  The
     aio_readv() system call first appeared in FreeBSD 13.0.

AUTHORS
     This manual page was written by Terry Lambert <terry@whistle.com>.

BUGS
     Invalid information in iocb->_aiocb_private may confuse the kernel.

FreeBSD 13.1-RELEASE-p6         January 2, 2021        FreeBSD 13.1-RELEASE-p6