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 arguments), 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 thereafter. 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 priority 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 reading.
-
-
- [
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.