AIO_READ(3)               (2020-06-09)                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 asyn-
          chronous 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(7) for
          details.

          If _POSIX_PRIORITIZED_IO is defined, and this file supports
          it, then the asynchronous operation is submitted at a prior-
          ity 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 off-
          set.

     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

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          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 start-
               ing 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).  allbox; lb lb lb l l l.
          Interface Attribute Value T{ aio_read() T}   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 control block must not be changed while the read opera-
          tion 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 struc-
          ture 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)

     COLOPHON

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          This page is part of release 5.10 of the Linux man-pages
          project.  A description of the project, information about
          reporting bugs, and the latest version of this page, can be
          found at https://www.kernel.org/doc/man-pages/.

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