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AIO_READ(3) Linux Programmer's Manual AIO_READ(3)

NAME

     aio_read - asynchronous read

SYNOPSIS

     #include <aio.h>

     int aio_read(struct aiocb *aiocbp);

     Link with -lrt.

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 sta-
     tus 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(7) 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 appropriately.  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.

VERSIONS

     The aio_read() function is available since glibc 2.1.

ATTRIBUTES

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

     +-----------+---------------+---------+
     |Interface  | Attribute     | Value   |
     +-----------+---------------+---------+
     |aio_read() | Thread safety | MT-Safe |
     +-----------+---------------+---------+

CONFORMING TO

     POSIX.1-2001, POSIX.1-2008.

NOTES

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

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

EXAMPLE

     See aio(7).