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PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       aio_read — asynchronous read from a file

SYNOPSIS

       #include <aio.h>

       int aio_read(struct aiocb *aiocbp);

DESCRIPTION

       The  aio_read()  function  shall  read  aiocbp->aio_nbytes  from  the file associated with
       aiocbp->aio_fildes into the buffer pointed to by aiocbp->aio_buf. The function call  shall
       return when the read request has been initiated or queued to the file or device (even when
       the data cannot be delivered immediately).

       If prioritized I/O is supported for this file, then the asynchronous  operation  shall  be
       submitted  at a priority equal to a base scheduling priority minus aiocbp->aio_reqprio. If
       Thread Execution Scheduling is not supported, then the base scheduling priority is that of
       the calling process;
       otherwise, the base scheduling priority is that of the calling thread.

       The  aiocbp  value  may be used as an argument to aio_error() and aio_return() in order to
       determine the error status and return status, respectively, of the asynchronous  operation
       while  it is proceeding. If an error condition is encountered during queuing, the function
       call shall return without having initiated or queued the request. The requested  operation
       takes  place  at  the  absolute position in the file as given by aio_offset, as if lseek()
       were called immediately prior to the operation with an offset equal to  aio_offset  and  a
       whence  equal  to  SEEK_SET.   After  a  successful  call  to  enqueue an asynchronous I/O
       operation, the value of the file offset for the file is unspecified.

       The aio_sigevent member specifies the  notification  which  occurs  when  the  request  is
       completed.

       The aiocbp->aio_lio_opcode field shall be ignored by aio_read().

       The  aiocbp  argument  points  to  an  aiocb  structure.  If  the  buffer  pointed  to  by
       aiocbp->aio_buf or the control block pointed to by aiocbp becomes an illegal address prior
       to asynchronous I/O completion, then the behavior is undefined.

       Simultaneous asynchronous operations using the same aiocbp produce undefined results.

       If  synchronized  I/O  is  enabled  on  the  file  associated with aiocbp->aio_fildes, the
       behavior of this function shall be according to the definitions of synchronized  I/O  data
       integrity completion and synchronized I/O file integrity completion.

       For  any  system action that changes the process memory space while an asynchronous I/O is
       outstanding to the address range being changed, the result of that action is undefined.

       For regular files, no data transfer shall occur past the offset maximum established in the
       open file description associated with aiocbp->aio_fildes.

RETURN VALUE

       The  aio_read()  function shall return the value zero if the I/O operation is successfully
       queued; otherwise, the function shall return the value -1 and set errno  to  indicate  the
       error.

ERRORS

       The aio_read() function shall fail if:

       EAGAIN The  requested  asynchronous  I/O  operation  was not queued due to system resource
              limitations.

       Each of the following conditions may be detected synchronously at the time of the call  to
       aio_read(),  or asynchronously. If any of the conditions below are detected synchronously,
       the aio_read() function shall return -1 and set errno to the corresponding value.  If  any
       of the conditions below are detected asynchronously, the return status of the asynchronous
       operation is set to -1, and the error status of the asynchronous operation is set  to  the
       corresponding value.

       EBADF  The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.

       EINVAL The file offset value implied by aiocbp->aio_offset would be invalid,
              aiocbp->aio_reqprio  is  not  a  valid  value,  or aiocbp->aio_nbytes is an invalid
              value.

       In the case that the aio_read() successfully queues the I/O operation but the operation is
       subsequently  canceled  or  encounters  an  error,  the  return status of the asynchronous
       operation is one of the values normally returned by the read() function call. In addition,
       the  error  status  of  the  asynchronous  operation  is  set to one of the error statuses
       normally set by the read() function call, or one of the following values:

       EBADF  The aiocbp->aio_fildes argument is not a valid file descriptor open for reading.

       ECANCELED
              The requested I/O was  canceled  before  the  I/O  completed  due  to  an  explicit
              aio_cancel() request.

       EINVAL The file offset value implied by aiocbp->aio_offset would be invalid.

       The following condition may be detected synchronously or asynchronously:

       EOVERFLOW
              The  file is a regular file, aiobcp->aio_nbytes is greater than 0, and the starting
              offset in aiobcp->aio_offset is before the end-of-file and  is  at  or  beyond  the
              offset maximum in the open file description associated with aiocbp->aio_fildes.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       aio_cancel(), aio_error(), lio_listio(), aio_return(), aio_write(), close(), exec, exit(),
       fork(), lseek(), read()

       The Base Definitions volume of POSIX.1‐2017, <aio.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .