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aio_read - Queues a single asynchronous read request
int aio_read (
struct aiocb *aiocbp );
Asynchronous I/O Library (libaio, libaio_raw)
A pointer to an aiocb structure.
The aio_read function allows the calling process to asynchronously read
aiocbp->aio_nbytes from the file associated with aiocbp->aio_fildes into
the buffer pointed to by aiocbp->aio_buf.
The aio_read function issues a read request and returns even when the data
cannot be delivered immediately. If the request cannot be initiated, the
aio_read function returns with an error status. If an error condition
occurs during queuing, the function call returns without initiating the
queue request. The aiocbp value may be used as an argument to the aio_error
and aio_return functions to determine the error or return status of the
asynchronous read operation.
The requested operation takes place at the absolute position in the file as
given by aio_offset, as if lseek() were called immediately prior to the
operation with an offset equal to aio_offset and a whence equal to
The aiocbp argument points to an asynchronous control block structure,
aiocb, used in the asynchronous I/O interfaces. The aiocb structure
contains asynchronous operation information, such as the file offset for
the read operation. The aiocb structure has the following members:
The aio_fildes member is the file descriptor on which the asynchronous
operation is to be performed. After any asynchronous I/O operation, the
aio_offset member is undefined and must be set explicitly for every
asynchronous I/O request.
The aio_nbytes and aio_buf members are the same as the nbyte and buf
arguments defined by POSIX.1 read and write functions.
The aio_sigevent member of the aiocb structure defines the signal generated
when the I/O operation is complete. If aio_sigevent.sigev_notify equals
SIGEV_SIGNAL and aio_sigevent.sigev_signo is non-zero, a signal is
generated when the asynchronous read operation has completed.
The aio_lio_opcode and aio_reqprio members are ignored by aio_read().
Pending asynchronous I/O operations are handled as follows:
· On close, _exit, or exec, any I/O that was directed to a file system
file, a tty device, or a streams device is canceled. Any I/O that was
directed to any raw character device, excluding terminal and streams
devices, is not canceled.
· On fork, no asynchronous I/O is inherited.
On an unsuccessful call, a value of -1 is returned and errno is set to
indicate the type of error that occurred.
The aio_read function fails under the following conditions:
The requested asynchronous I/O operation was not queued due to system
The aiocbp->aio_fildes argument is not a valid file descriptor open for
The file offset value implied by aiocbp->aio_offset would be invalid.
On a successful call, a value of 0 (zero) is returned and the I/O operation
is queued. After successful queuing of aio_read, return and error values
are the same as for a call to the read function. One of the following
additional errors may occur:
The operation was canceled by aio_cancel.
The offset in aio_offset is invalid for the file specified.
Functions: close(2), exec(2), _exit(2), fork(2), lseek(2), read(2),
write(2), aio_cancel(3), aio_error(3), aio_group_completion_np(3),
aio_results_np(3), aio_return(3), aio_suspend(3), aio_write(3),
Guide to Realtime Programming
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