NAME

       aio_read — asynchronous read from a file (REALTIME)

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <aio.h>

       int
       aio_read(struct aiocb *iocb);

DESCRIPTION

       The  aio_read()  system  call  allows  the  calling  process to read iocb->aio_nbytes from the descriptor
       iocb->aio_fildes beginning at the offset iocb->aio_offset into the buffer pointed  to  by  iocb->aio_buf.
       The  call returns 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.

       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() system call.

       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() function returns 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() system call will fail if:

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

       [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() system call is made, or
       asynchronously, at any time thereafter.  If they are detected at call time,  aio_read()  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.

HISTORY

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

AUTHORS

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

BUGS

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

Debian                                           August 19, 2016                                     AIO_READ(2)