aio_write(3aio)

aio_write, aio_write64 -- asynchronous write

Synopsis

   
   cc [options] -Kthread file
   

   #include <aio.h>
   

   int aio_write(struct aiocb *aiocbp);
   

   int aio_write64(struct aiocb64 *aiocbp);

Description

aio_write supports an asynchronous write capability. aio_write allows you to write aio_nbytes to the file associated with file descriptor aio_fildes from the buffer pointed to by aio_buf.

aiocbp points to an aiocb structure which contains other input parameters as well as completion status members.

If you do not wish to be notified of completion, you should set aio_sigevent.sigev_notify to SIGEV_NONE in the asynchronous I/O control block. If you require notification, you must set the aio_sigevent.sigev_notify to SIGEV_CALLBACK, aio_sigevent.sigev_func to the address of the function to be called, and aio_sigevent.sigev_value to the argument to be passed to the function. You may also want the aio_sigevent.sigev_value to be the address of the asynchronous I/O control block that was used to initiate the I/O request. [See aiocb(5)].

If the control block pointed to by aiocbp or the buffer pointed to by aio_buf becomes an invalid address prior to asynchronous I/O completion, then the behavior is undefined.

The call to aio_write returns 0 when the write request has been initiated or queued to the file or device. If an error condition is encountered during queuing, the call returns -1 without having initiated or queued the request.

Return values

A call to aio_write or aio_write64 returns 0 when the write request has been initiated or queued to the file or device. If an error condition is encountered during queuing, the call returns -1 without having initiated or queued the request. When the call has completed successfully, aio_write and aio_write64 return 0 and the structure member aio_errno is set to EINPROGRESS. When a call to aio_write or aio_write64 fails, After the write operation has successfully completed, the aio_errno structure member is set to 0. The aio_return function can be used to access the return value of the underlying write call.

Errors

There are two types of errors that are associated with an asynchronous I/O request. The first occurs during the validity checking of the I/O request submitted by the aio_write or aio_write64 routines. This error is returned to the caller of aio_write or aio_write64. The other occurs during the processing of the actual write operation. The write operation may fail for any of the reasons that a normal write may fail. If a call to aio_write or aio_write64 successfully queues the I/O operation but the operation is subsequently canceled or encounters an error, the aio_error function will return one of the values normally returned by the write system call or one of the errors listed below. The time at which the error occurs is implementation-dependent; for example, an invalid file descriptor may not be determined at the time of the call to aio_write aio_write64 which could successfully complete. However, aio_error will return EBADF to indicate the error.

The notification specified for a request will only be performed if that request was successfully queued.

Under the following conditions, aio_write fails and sets errno or the aio_errno structure member to:

EFBIG: The file is a regular file, aiocbp->aio_nbytes is greater than 0 and the starting offset in aiocbp->aio_offset is at or beyond the offset maximum in the open file descriptor associated with aio_fildes.

Under the following conditions, aio_write and aio_write64 fail and set errno or the aio_errno structure member to:

EAGAIN: The requested asynchronous I/O operation was not queued because of system resource limitations. The first request to encounter a resource limitation and all subsequent requests will be marked so that aio_error returns EAGAIN.
EFAULT: aiocbp or the aio_buf member points outside the allocated address space.
ECANCELED: The requested I/O was canceled before the I/O completed due to aio_cancel.
EINVAL: On SVR4.2, the request does not have the AIO_RAW flag bit set in aio_flags.
ENOMEM: There were no internal kernal aio control blocks available to service the request (number of kernel aio control blocks is tunable via the NUMAIO kernel parameter; see ``Miscellaneous parameters'' in Monitoring and tuning the system).

References

aio_cancel(3aio), aiocb(5), aio_read(3aio), aio_suspend(3aio), intro(2), write(2)

Notices

When developing applications for both SVR4.2 and future versions, the AIO_RAW flag should be set in aio_flags to insure that performance is maintained.

Considerations for large file support

aio_write64 supports large files, but is otherwise identical to aio_write. For details on programming for large file capable applications, see ``Large File Support'' on intro(2).