|AIO_READ(2)||System Calls Manual||AIO_READ(2)|
LIBRARY¶Standard C Library (libc, -lc)
aio_read() system call allows the calling process to read iocb->aio_nbytes from the descriptor iocb->aio_fildes beginning at the offset iocb->aio_offset into the buffer pointed to by iocb->aio_buf. The call returns immediately after the read request has been enqueued to the descriptor; the read may or may not have completed at the time the call returns.
If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then the enqueued operation is submitted at a priority equal to that of the calling process minus iocb->aio_reqprio.
The iocb->aio_lio_opcode argument is
ignored by the
aio_read() system call.
The iocb pointer may be subsequently used as
an argument to
aio_error() in order to determine return or error
status for the enqueued operation while it is in progress.
If the request could not be enqueued (generally due to invalid arguments), then the call returns without having enqueued the request.
If the request is successfully enqueued, the value of iocb->aio_offset can be modified during the request as context, so this value must not be referenced after the request is enqueued.
The iocb->aio_sigevent structure can be used to request notification of the operation's completion as described in aio(4).
RESTRICTIONS¶The Asynchronous I/O Control Block structure pointed to by iocb and the buffer that the iocb->aio_buf member of that structure references must remain valid until the operation has completed.
The asynchronous I/O control buffer iocb
should be zeroed before the
aio_read() call to avoid
passing bogus context information to the kernel.
Modifications of the Asynchronous I/O Control Block structure or the buffer contents are not allowed while the request is queued.
If the file offset in iocb->aio_offset is past the offset maximum for iocb->aio_fildes, no I/O will occur.
aio_read() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
aio_read() system call will fail if:
- The request was not queued because of system resource limitations.
- The asynchronous notification method in iocb->aio_sigevent.sigev_notify is invalid or not supported.
- Asynchronous read operations on the file descriptor iocb->aio_fildes are unsafe and unsafe asynchronous I/O operations are disabled.
The following conditions may be synchronously detected when the
aio_read() system call is made, or asynchronously,
at any time thereafter. If they are detected at call time,
aio_read() returns -1 and sets
errno appropriately; otherwise the
aio_return() system call must be called, and will
return -1, and
aio_error() must be called to
determine the actual value that would have been returned in
- The iocb->aio_fildes argument is invalid.
- The offset iocb->aio_offset is not valid, the priority specified by iocb->aio_reqprio is not a valid priority, or the number of bytes specified by iocb->aio_nbytes is not valid.
- The file is a regular file, iocb->aio_nbytes is greater than zero, the starting offset in iocb->aio_offset is before the end of the file, but is at or beyond the iocb->aio_fildes offset maximum.
If the request is successfully enqueued, but subsequently
cancelled or an error occurs, the value returned by the
aio_return() system call is per the
read(2) system call, and the value returned by the
aio_error() system call is either one of the error
returns from the read(2) system call, or one of:
SEE ALSO¶aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), aio_waitcomplete(2), aio_write(2), sigevent(3), siginfo(3), aio(4)
aio_read() system call is expected to conform to the IEEE Std 1003.1 (“POSIX.1”) standard.
aio_read() system call first appeared in FreeBSD 3.0.
AUTHORS¶This manual page was written by Terry Lambert <email@example.com>.
BUGS¶Invalid information in iocb->_aiocb_private may confuse the kernel.
|August 19, 2016||Linux 4.9.0-9-amd64|