NAME

       aio_read - asynchronous read

LIBRARY

       Real-time library (librt, -lrt)

SYNOPSIS

       #include <aio.h>

       int aio_read(struct aiocb *aiocbp);

DESCRIPTION

       The  aio_read()  function  queues  the  I/O  request described by the buffer pointed to by
       aiocbp.  This function is the asynchronous analog of read(2).  The arguments of the call

           read(fd, buf, count)

       correspond (in order) to the fields aio_fildes, aio_buf, and aio_nbytes of  the  structure
       pointed to by aiocbp.  (See aio(7) for a description of the aiocb structure.)

       The  data  is read starting at the absolute position aiocbp->aio_offset, regardless of the
       file offset.  After the call, the value of the file offset is unspecified.

       The "asynchronous" means that this call returns as soon as the request has been  enqueued;
       the  read  may  or may not have completed when the call returns.  One tests for completion
       using aio_error(3).  The return status of a completed I/O operation  can  be  obtained  by
       aio_return(3).   Asynchronous  notification  of  I/O completion can be obtained by setting
       aiocbp->aio_sigevent appropriately; see sigevent(3type) for details.

       If _POSIX_PRIORITIZED_IO is defined, and this file  supports  it,  then  the  asynchronous
       operation  is  submitted  at  a  priority  equal  to  that  of  the  calling process minus
       aiocbp->aio_reqprio.

       The field aiocbp->aio_lio_opcode is ignored.

       No data is read from a regular file beyond its maximum offset.

RETURN VALUE

       On success, 0 is returned.  On error, the request is not enqueued,  -1  is  returned,  and
       errno  is  set  to  indicate  the  error.   If an error is detected only later, it will be
       reported via aio_return(3) (returns status -1) and aio_error(3) (error status—whatever one
       would have gotten in errno, such as EBADF).

ERRORS

       EAGAIN Out of resources.

       EBADF  aio_fildes is not a valid file descriptor open for reading.

       EINVAL One or more of aio_offset, aio_reqprio, or aio_nbytes are invalid.

       ENOSYS aio_read() is not implemented.

       EOVERFLOW
              The  file  is a regular file, we start reading before end-of-file and want at least
              one byte, but the starting position is past the maximum offset for this file.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                      │ Attribute     │ Value   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │aio_read()                                                     │ Thread safety │ MT-Safe │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       glibc 2.1.  POSIX.1-2001.

NOTES

       It is a good idea to zero out the control block before use.  The control block must not be
       changed while the read operation is in progress.  The buffer area being read into must not
       be accessed during the operation  or  undefined  results  may  occur.   The  memory  areas
       involved must remain valid.

       Simultaneous I/O operations specifying the same aiocb structure produce undefined results.

EXAMPLES

       See aio(7).

SEE ALSO

       aio_cancel(3),  aio_error(3),  aio_fsync(3),  aio_return(3), aio_suspend(3), aio_write(3),
       lio_listio(3), aio(7)