FreeBSD Manual Pages
AIO_WRITE(2) System Calls Manual AIO_WRITE(2) NAME aio_write, aio_write2, aio_writev -- asynchronous write to a file (REAL- TIME) LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <aio.h> int aio_write(struct aiocb *iocb); int aio_write2(struct aiocb *iocb, int flags); #include <sys/uio.h> int aio_writev(struct aiocb *iocb); DESCRIPTION The aio_write(), aio_write2(), and aio_writev() system calls allow the calling process to write to the descriptor iocb->aio_fildes. The syscalls return immediately after the write request has been enqueued to the de- scriptor; the write may or may not have completed at the time the call re- turns. The aio_write() call will write iocb->aio_nbytes from the buffer pointed to by iocb->aio_buf, whereas aio_writev() gathers the data from the iocb->aio_iovcnt buffers specified by the members of the iocb->aio_iov ar- ray. If the request could not be enqueued, generally due to invalid arguments, the call returns without having enqueued the request. For aio_writev() the iovec structure is defined in writev(2). If O_APPEND is set for iocb->aio_fildes, 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 for aio_write() will occur at the absolute position from the beginning of the file plus iocb->aio_offset. The aio_write2() call takes the flags argument. If flags is passed as zero, the call behaves identically to aio_write(). The following flags can be specified by logical or: AIO_OP2_FOFFSET The write for non O_APPEND file descriptors occurs at the file descriptor offset, which is advanced by the opera- tion as done by the write(2) syscall. The iocb->aio_offset field is ignored. AIO_OP2_VECTORED Similar to aio_writev(), the write buffers are specified by the aiocb->aio_iov array. The iocb pointer may be subsequently used as an argument to aio_return() and aio_error() in order to determine return or error status for the en- queued operation while it is in progress. 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 refer- enced 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 re- main valid until the operation has completed. The asynchronous I/O control buffer iocb should be zeroed before the system calls 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. RETURN VALUES The aio_write() and aio_writev() functions return the value 0 if success- ful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS The aio_write(), aio_write2(), and aio_writev() system calls will fail if: [EAGAIN] The request was not queued because of system resource limitations. [EFAULT] Part of aio_iov points outside the process's allocated address space. [EINVAL] The asynchronous notification method in iocb->aio_sigevent.sigev_notify is invalid or not sup- ported. [EOPNOTSUPP] Asynchronous write 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_write(), aio_write2(), or aio_writev() system call is made, or asyn- chronously, at any time thereafter. If they are detected at call time, the calls return -1 and set 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 errno. [EBADF] The iocb->aio_fildes argument is invalid, or is not opened for writing. [EINVAL] 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. If the request is successfully enqueued, but subsequently canceled or an error occurs, the value returned by the aio_return() system call is per the write(2) system call, and the value returned by the aio_error() system call is either one of the error returns from the write(2) system call, or one of: [EBADF] The iocb->aio_fildes argument is invalid for writing. [ECANCELED] The request was explicitly canceled via a call to aio_cancel(). [EINVAL] The offset iocb->aio_offset would be invalid. SEE ALSO aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), aio_waitcom- plete(2), sigevent(3), siginfo(3), aio(4) STANDARDS The aio_write() system call is expected to conform to the IEEE Std 1003.1 ("POSIX.1") standard. The aio_write2() and aio_writev() system calls are FreeBSD extensions, and should not be used in portable code. HISTORY The aio_write() system call first appeared in FreeBSD 3.0. The aio_writev() system call first appeared in FreeBSD 13.0. The aio_write2() system call first appeared in FreeBSD 14.1. AUTHORS This manual page was written by Wes Peters <wes@softweyr.com>. BUGS Invalid information in iocb->_aiocb_private may confuse the kernel. FreeBSD ports 15.quarterly March 27, 2025 AIO_WRITE(2)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RESTRICTIONS | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | AUTHORS | BUGS
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