DragonFly On-Line Manual Pages

Search: Section:  

AIO_READ(3)           DragonFly Library Functions Manual           AIO_READ(3)


aio_read -- asynchronous read from a file (REALTIME)


POSIX Real-time Library (librt, -lrt)


#include <time.h> #include <aio.h> int aio_read(struct aiocb *iocb);


The aio_read() function 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 function returns immediately after the read request has been enqueued to the descriptor; the read may or may not have completed at the time the function 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 is ignored by the aio_read() function. 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 function 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.


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() function . Modifications of the Asynchronous I/O Control Block structure or the buf- fer 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.


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.




The aio_read() function will fail if: [EAGAIN] The request was not queued because of system resource limitations. [ENOSYS] The aio_read() function is not supported. The following conditions may be synchronously detected when the aio_read() function is made, or asynchronously, at any time thereafter. If they are detected at call time, aio_read() returns -1 and sets errno appropriately; otherwise the aio_return() function 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] iocb->aio_fildes 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() function is per the read(2) call, and the value returned by the aio_error() function is either one of the error returns from the read(2) call, or one of: [EBADF] iocb->aio_fildes 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.


The aio_read() function is expected to conform to the IEEE Std 1003.2 (``POSIX.2'') standard.


The aio_read function first appeared in FreeBSD 3.0.


This manual page was written by Terry Lambert <terry@whistle.com>. DragonFly 3.5 November 17, 1998 DragonFly 3.5

Search: Section: