freebsd-src/lib/libsys/lio_listio.2

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.Dd January 13, 2024
.Dt LIO_LISTIO 2
.Os
.Sh NAME
.Nm lio_listio
.Nd "list directed I/O (REALTIME)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In aio.h
.Ft int
.Fo lio_listio
.Fa "int mode"
.Fa "struct aiocb * const list[]"
.Fa "int nent"
.Fa "struct sigevent *sig"
.Fc
.Sh DESCRIPTION
The
.Fn lio_listio
function initiates a list of I/O requests with a single function call.
The
.Fa list
argument is an array of pointers to
.Vt aiocb
structures describing each operation to perform,
with
.Fa nent
elements.
.Dv NULL
elements are ignored.
.Pp
The
.Va aio_lio_opcode
field of each
.Vt aiocb
specifies the operation to be performed.
The following operations are supported:
.Bl -tag -width ".Dv LIO_WRITE"
.It Dv LIO_READ
Read data as if by a call to
.Xr aio_read 2 .
.It Dv LIO_READV
Read data as if by a call to
.Xr aio_readv 2 .
.It Dv LIO_NOP
No operation.
.It Dv LIO_WRITE
Write data as if by a call to
.Xr aio_write 2 .
.It Dv LIO_WRITEV
Write data as if by a call to
.Xr aio_writev 2 .
.El
.Pp
If the
.Dv LIO_READ ,
.Dv LIO_READV ,
.Dv LIO_WRITE ,
.Dv LIO_WRITEV
opcodes are or-ed with the
.Dv LIO_FOFFSET
flag, the corresponding read or write operation uses the current file
descriptor offset instead of
.Va aio_offset
from
.Vt aiocb .
.Pp
If the
.Fa mode
argument is
.Dv LIO_WAIT ,
.Fn lio_listio
does not return until all the requested operations have been completed.
If
.Fa mode
is
.Dv LIO_NOWAIT ,
.Fa sig
can be used to request asynchronous notification when all operations have
completed.
If
.Fa sig
is
.Dv NULL ,
no notification is sent.
.Pp
For
.Dv SIGEV_KEVENT
notifications,
the posted kevent will contain:
.Bl -column ".Va filter"
.It Sy Member Ta Sy Value
.It Va ident Ta Fa list
.It Va filter Ta Dv EVFILT_LIO
.It Va udata Ta
value stored in
.Fa sig->sigev_value
.El
.Pp
For
.Dv SIGEV_SIGNO
and
.Dv SIGEV_THREAD_ID
notifications,
the information for the queued signal will include
.Dv SI_ASYNCIO
in the
.Va si_code
field and the value stored in
.Fa sig->sigev_value
in the
.Va si_value
field.
.Pp
For
.Dv SIGEV_THREAD
notifications,
the value stored in
.Fa sig->sigev_value
is passed to the
.Fa sig->sigev_notify_function
as described in
.Xr sigevent 3 .
.Pp
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, ...,
.Fa nent Ns \-1 .
.Sh RETURN VALUES
If
.Fa mode
is
.Dv LIO_WAIT ,
the
.Fn lio_listio
function returns 0 if the operations completed successfully,
otherwise \-1.
.Pp
If
.Fa mode
is
.Dv LIO_NOWAIT ,
the
.Fn lio_listio
function returns 0 if the operations are successfully queued,
otherwise \-1.
.Sh ERRORS
The
.Fn lio_listio
function will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
There are not enough resources to enqueue the requests.
.It Bq Er EAGAIN
The request would cause the system-wide limit
.Dv {AIO_MAX}
to be exceeded.
.It Bq Er EINVAL
The
.Fa mode
argument is neither
.Dv LIO_WAIT
nor
.Dv LIO_NOWAIT ,
or
.Fa nent
is greater than
.Dv {AIO_LISTIO_MAX} .
.It Bq Er EINVAL
The asynchronous notification method in
.Fa sig->sigev_notify
is invalid or not supported.
.It Bq Er EINTR
A signal interrupted the system call before it could be completed.
.It Bq Er EIO
One or more requests failed.
.El
.Pp
In addition, the
.Fn lio_listio
function may fail for any of the reasons listed for
.Xr aio_read 2
and
.Xr aio_write 2 .
.Pp
If
.Fn lio_listio
succeeds, or fails with an error code of
.Er EAGAIN , EINTR ,
or
.Er EIO ,
some of the requests may have been initiated.
The caller should check the error status of each
.Vt aiocb
structure individually by calling
.Xr aio_error 2 .
.Sh SEE ALSO
.Xr aio_error 2 ,
.Xr aio_read 2 ,
.Xr aio_readv 2 ,
.Xr aio_write 2 ,
.Xr aio_writev 2 ,
.Xr read 2 ,
.Xr write 2 ,
.Xr sigevent 3 ,
.Xr siginfo 3 ,
.Xr aio 4
.Sh STANDARDS
The
.Fn lio_listio
function is expected to conform to
.St -p1003.1-2001 .
The
.Dv LIO_READV
and
.Dv LIO_WRITEV
operations are
.Fx extensions, and should not be used in portable code.
.Sh HISTORY
The
.Fn lio_listio
system call first appeared in
.Fx 3.0 .