LIO_LISTIO(2) System Calls Manual LIO_LISTIO(2)

lio_listio — list directed I/O (REALTIME)

Standard C Library (libc, -lc)

#include <aio.h>
#include <sys/uio.h>

int
lio_listio(int mode, struct aiocb * const list[], int nent, struct sigevent *sig);

The () function initiates a list of I/O requests with a single function call. The list argument is an array of pointers to aiocb structures describing each operation to perform, with nent elements. NULL elements are ignored.

The aio_lio_opcode field of each aiocb specifies the operation to be performed. The following operations are supported:

Read data as if by a call to aio_read(2).
Read data from multiple buffers as if by a call to aio_read(2).
No operation.
Write data as if by a call to aio_write(2).
Write data from multiple buffers as if by a call to aio_write(2).

If the mode argument is LIO_WAIT, () does not return until all the requested operations have been completed. If mode is LIO_NOWAIT, sig can be used to request asynchronous notification when all operations have completed. If sig is NULL, no notification is sent.

For SIGEV_KEVENT notifications, the sigev_notify field should be set to SIGEV_KEVENT, and its sigevent's sigev_signo field should contain the descriptor of the kqueue that the event should be attached to.

Individual aiocb entries in the list that have their own SIGEV_KEVENT notifications configured will receive EVFILT_AIO events upon completion with I/O results (error status and return value).

When sig is configured for SIGEV_KEVENT notifications, when all I/O operations in the list have completed, EVFILT_LIO kevents will be posted for all entries in the list. The I/O results (error status and return value) will be delivered with these EVFILT_LIO events.

Each posted kevent will contain:

ident aiocb entry
filter or EVFILT_LIO
udata value stored in sig->sigev_value

When using SIGEV_KEVENT notifications, if () returns 0, all operations will generate kevent notifications, even if some operations encounter enqueue failures. If lio_listio() returns an error, no operations were successfully enqueued and no kevent notifications will be generated.

The order in which the requests are carried out is not specified; in particular, there is no guarantee that they will be executed in the order 0, 1, ..., nent-1.

If mode is LIO_WAIT, the lio_listio() function returns 0 if the operations completed successfully, otherwise -1 and the global variable errno is set to indicate the error.

If mode is LIO_NOWAIT, the lio_listio() function returns 0 if the operations are successfully queued, otherwise -1 and the global variable errno is set to indicate the error.

The lio_listio() function will fail if:

[]
There are not enough resources to enqueue the requests.
[]
The request would cause the system-wide limit {AIO_MAX} to be exceeded.
[]
The mode argument is neither LIO_WAIT nor LIO_NOWAIT, or nent is greater than {AIO_LISTIO_MAX}.
[]
The asynchronous notification method in sig->sigev_notify is invalid or not supported.
[]
An attempt was made to register both EVFILT_AIO and EVFILT_LIO kevent notifications on the same aiocb.
[]
A signal interrupted the system call before it could be completed.
[]
One or more requests failed.

In addition, the lio_listio() function may fail for any of the reasons listed for aio_read(2), and aio_write(2).

If lio_listio() succeeds, or fails with an error code of EAGAIN, EINTR, or EIO, some of the requests may have been initiated. The caller should check the error status of each aiocb structure individually by calling aio_error(2).

aio_error(2), aio_read(2), aio_write(2), aio(4)

The lio_listio() function is expected to conform to IEEE Std 1003.1-2001 (“POSIX.1”) standard.

The lio_listio() system call first appeared in FreeBSD 3.0.

January 13, 2024 Mac OS X 13