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AIO_READ(2) FreeBSD System Calls Manual AIO_READ(2) NAME aio_read -- asynchronous read from a file (REALTIME) LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <aio.h> int aio_read(struct aiocb *iocb); DESCRIPTION The aio_read() system call allows the calling process to read iocb-_aio_nbytes from the descriptor iocb-_aio_fildes beginning at the offset iocb-_aio_offset into the buffer pointed to by iocb-_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 iocb-_aio_reqprio. The iocb-_aio_lio_opcode argument is ignored by the aio_read() system call. 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 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 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 iocb and the buffer that the 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 iocb 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 iocb-_aio_offset is past the offset maximum for iocb-_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. [ENOSYS] The aio_read() system call is not supported. 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 iocb-_aio_fildes argument is invalid. [EINVAL] The offset iocb-_aio_offset is not valid, the priority specified by iocb-_aio_reqprio is not a valid prior- ity, or the number of bytes specified by iocb-_aio_nbytes is not valid. [EOVERFLOW] The file is a regular file, iocb-_aio_nbytes is greater than zero, the starting offset in iocb-_aio_offset is before the end of the file, but is at or beyond the iocb-_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 iocb-_aio_fildes argument is invalid for reading. [ECANCELED] The request was explicitly cancelled 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_waitcomplete(2), aio_write(2), aio(4) STANDARDS The aio_read() system call is expected to conform to the IEEE Std 1003.1 (``POSIX.1'') standard. HISTORY The aio_read() system call first appeared in FreeBSD 3.0. AUTHORS This manual page was written by Terry Lambert <terry@whistle.com>. BUGS Invalid information in iocb-__aiocb_private may confuse the kernel. FreeBSD 6.2 November 17, 1998 FreeBSD 6.2
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RESTRICTIONS | RETURN VALUES | DIAGNOSTICS | ERRORS | SEE ALSO | STANDARDS | HISTORY | AUTHORS | BUGS
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