aio_read(3) - NetBSD Manual Pages

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AIO_READ(3)             NetBSD Library Functions Manual            AIO_READ(3)


NAME
aio_read -- asynchronous read from a file (REALTIME)
LIBRARY
POSIX Real-time Library (librt, -lrt)
SYNOPSIS
#include <aio.h> int aio_read(struct aiocb *aiocbp);
DESCRIPTION
The aio_read() system call allows the calling process to read aiocbp->aio_nbytes from the descriptor aiocbp->aio_fildes beginning at the offset aiocbp->aio_offset into the buffer pointed to by aiocbp->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 aiocbp->aio_reqprio. The aiocbp->aio_lio_opcode argument is ignored by the aio_read() system call. The aiocbp pointer may be subsequently used as an argument to aio_return() and 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 argu- ments), then the call returns without having enqueued the request. If the request is successfully enqueued, the value of aiocbp->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 aiocbp and the buffer that the 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. The asynchronous I/O control buffer aiocbp should be zeroed before the 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 aiocbp->aio_offset is past the offset maximum for aiocbp->aio_fildes, no I/O will occur.
RETURN VALUES
The aio_read() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
DIAGNOSTICS
None.
ERRORS
The aio_read() system call will fail if: [EAGAIN] The request was not queued because of system resource limitations. The following conditions may be synchronously detected when the aio_read() system call is made, or asynchronously, at any time there- after. If they are detected at call time, aio_read() returns -1 and sets 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 aiocbp->aio_fildes argument is invalid. [EINVAL] The offset aiocbp->aio_offset is not valid, the prior- ity specified by aiocbp->aio_reqprio is not a valid priority, or the number of bytes specified by aiocbp->aio_nbytes is not valid. [EOVERFLOW] The file is a regular file, aiocbp->aio_nbytes is greater than zero, the starting offset in aiocbp->aio_offset is before the end of the file, but is at or beyond the aiocbp->aio_fildes offset maximum. If the request is successfully enqueued, but subsequently cancelled or an error occurs, the value returned by the aio_return() system call is per the read(2) system call, and the value returned by the aio_error() system call is either one of the error returns from the read(2) system call, or one of: [EBADF] The aiocbp->aio_fildes argument is invalid for read- ing. [ECANCELED] The request was explicitly cancelled via a call to aio_cancel(). [EINVAL] The offset aiocbp->aio_offset would be invalid.
SEE ALSO
siginfo(2), aio(3)
STANDARDS
The aio_read() system call is expected to conform to the IEEE Std 1003.1-2001 (``POSIX.1'') standard.
HISTORY
The aio_read() system call first appeared in NetBSD 5.0. NetBSD 9.99 May 17, 2010 NetBSD 9.99
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