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)