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$FreeBSD: /repoman/r/ncvs/src/lib/libc/sys/aio_write.2,v 1.20 2005/12/13 13:43:35 davidxu Exp $
.Dd May 17, 2010 .Dt AIO_WRITE 3 .Os .Sh NAME .Nm aio_write .Nd asynchronous write to a file (REALTIME) .Sh LIBRARY .Lb librt .Sh SYNOPSIS n aio.h .Ft int .Fn aio_write "struct aiocb *aiocbp" .Sh DESCRIPTION The .Fn aio_write system call allows the calling process to write .Fa aiocbp->aio_nbytes from the buffer pointed to by .Fa aiocbp->aio_buf to the descriptor .Fa aiocbp->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.
p If .Dv O_APPEND is set for .Fa aiocbp->aio_fildes , .Fn aio_write operations append to the file in the same order as the calls were made. If .Dv 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 aiocbp->aio_offset .
p If .Dv _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 aiocbp->aio_reqprio .
p The .Fa aiocbp 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.
p If the request is successfully enqueued, the value of .Fa aiocbp->aio_offset can be modified during the request as context, so this value must not be referenced after the request is enqueued. .Sh RESTRICTIONS The Asynchronous I/O Control Block structure pointed to by .Fa aiocbp and the buffer that the .Fa aiocbp->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.
p The asynchronous I/O control buffer .Fa aiocbp should be zeroed before the .Fn aio_write system call to avoid passing bogus context information to the kernel.
p 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.
p If the file offset in .Fa aiocbp->aio_offset is past the offset maximum for .Fa aiocbp->aio_fildes , no I/O will occur. .Sh RETURN VALUES .Rv -std aio_write .Sh ERRORS The .Fn aio_write system call will fail if: l -tag -width Er t Bq Er EAGAIN The request was not queued because of system resource limitations. .El
p 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 .Va 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 .Va errno .
p l -tag -width Er t Bq Er EBADF The .Fa aiocbp->aio_fildes argument is invalid, or is not opened for writing. t Bq Er EINVAL The offset .Fa aiocbp->aio_offset is not valid, the priority specified by .Fa aiocbp->aio_reqprio is not a valid priority, or the number of bytes specified by .Fa aiocbp->aio_nbytes is not valid. .El
p 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 .Xr write 2 system call, and the value returned by the .Fn aio_error system call is either one of the error returns from the .Xr write 2 system call, or one of: l -tag -width Er t Bq Er EBADF The .Fa aiocbp->aio_fildes argument is invalid for writing. t Bq Er ECANCELED The request was explicitly canceled via a call to .Fn aio_cancel . t Bq Er EINVAL The offset .Fa aiocbp->aio_offset would be invalid. .El .Sh SEE ALSO .Xr siginfo 2 , .Xr aio 3 .Sh STANDARDS The .Fn aio_write system call is expected to conform to the .St -p1003.1-2001 standard. .Sh HISTORY The .Fn aio_write system call first appeared in .Nx 5.0 .
Indexes created Sat Sep 20 22:09:52 GMT 2025