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aio_write.2freebsd

BSD mandoc

NAME

aio_write - asynchronous write to a file (REALTIME)

LIBRARY

Lb libc

SYNOPSIS

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

DESCRIPTION

The Fn aio_write system call allows the calling process to write Fa iocb->aio_nbytes from the buffer pointed to by Fa iocb->aio_buf to the descriptor Fa iocb->aio_fildes . The call returns immediately after the write request has been enqueued to the descriptor; the write may or may not have completed at the time the call returns. If the request could not be enqueued, generally due to invalid arguments, the call returns without having enqueued the request.

If O_APPEND is set for Fa iocb->aio_fildes , Fn aio_write operations append to the file in the same order as the calls were made. If O_APPEND is not set for the file descriptor, the write operation will occur at the absolute position from the beginning of the file plus Fa iocb->aio_offset .

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 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 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_write system 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_write

ERRORS

The Fn aio_write system call will fail if:

Bq Er EAGAIN

The request was not queued because of system resource limitations.

Bq Er ENOSYS

The Fn aio_write system call is not supported.

The following conditions may be synchronously detected when the Fn aio_write system call is made, or asynchronously, at any time thereafter. If they are detected at call time, Fn aio_write 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, or is not opened for writing.

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.

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

Bq Er EBADF

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

Bq Er ECANCELED

The request was explicitly canceled 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, siginfo(3), aio(4)

STANDARDS

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

HISTORY

The Fn aio_write system call first appeared in Fx 3.0 .

AUTHORS

This manual page was written by An Wes Peters Aq wes@softweyr.com .

BUGS

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