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aio_read

BSD mandoc

NAME

aio_read - asynchronous read from a file (REALTIME)

LIBRARY

Lb libc

SYNOPSIS

In aio.h Ft int Fn aio_read struct aiocb *iocb

DESCRIPTION

The Fn aio_read system call allows the calling process to read Fa iocb->aio_nbytes from the descriptor Fa iocb->aio_fildes beginning at the offset Fa iocb->aio_offset into the buffer pointed to by Fa 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 Fa iocb->aio_reqprio .

The Fa iocb->aio_lio_opcode argument is ignored by the Fn aio_read system call.

The Fa iocb pointer may be subsequently used as an argument to Fn aio_return and Fn 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 Fa iocb->aio_offset can be modified during the request as context, so this value must not be referenced after the request is enqueued.

RESTRICTIONS

The Asynchronous I/O Control Block structure pointed to by Fa iocb and the buffer that the Fa iocb->aio_buf member of that structure references must remain valid until the operation has completed. For this reason, use of auto (stack) variables for these objects is discouraged.

The asynchronous I/O control buffer Fa iocb should be zeroed before the Fn 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 after the request has been enqueued, but before the request has completed, are not allowed.

If the file offset in Fa iocb->aio_offset is past the offset maximum for Fa iocb->aio_fildes , no I/O will occur.

RETURN VALUES

Rv -std aio_read

DIAGNOSTICS

None.

ERRORS

The Fn aio_read system call will fail if:

Bq Er EAGAIN

The request was not queued because of system resource limitations.

Bq Er ENOSYS

The Fn aio_read system call is not supported.

The following conditions may be synchronously detected when the Fn aio_read system call is made, or asynchronously, at any time thereafter. If they are detected at call time, Fn aio_read returns -1 and sets errno appropriately; otherwise the Fn aio_return system call must be called, and will return -1, and Fn aio_error must be called to determine the actual value that would have been returned in errno

Bq Er EBADF

The Fa iocb->aio_fildes argument is invalid.

Bq Er EINVAL

The offset Fa iocb->aio_offset is not valid, the priority specified by Fa iocb->aio_reqprio is not a valid priority, or the number of bytes specified by Fa iocb->aio_nbytes is not valid.

Bq Er EOVERFLOW

The file is a regular file, Fa iocb->aio_nbytes is greater than zero, the starting offset in Fa iocb->aio_offset is before the end of the file, but is at or beyond the Fa iocb->aio_fildes offset maximum.

If the request is successfully enqueued, but subsequently cancelled or an error occurs, the value returned by the Fn aio_return system call is per the read(2) system call, and the value returned by the Fn aio_error system call is either one of the error returns from the read(2) system call, or one of:

Bq Er EBADF

The Fa iocb->aio_fildes argument is invalid for reading.

Bq Er ECANCELED

The request was explicitly cancelled via a call to Fn aio_cancel .

Bq Er EINVAL

The offset Fa iocb->aio_offset would be invalid.

SEE ALSO

aio_cancel2, aio_error2, aio_return2, aio_suspend2, aio_waitcomplete2, aio_write2, aio(4)

STANDARDS

The Fn aio_read system call is expected to conform to the St -p1003.1 standard.

HISTORY

The Fn aio_read system call first appeared in Fx 3.0 .

AUTHORS

This manual page was written by An Terry Lambert Aq terry@whistle.com .

BUGS

Invalid information in Fa iocb->_aiocb_private may confuse the kernel.