.\" Copyright 2003, Free Software Foundation, Inc.
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.TH io_submit 2 2026-04-11 "Linux man-pages 6.18"
.SH NAME
io_submit \- submit asynchronous I/O blocks for processing
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <linux/aio_abi.h>
.BR "#include <sys/syscall.h>" "    /* Definition of SYS_* constants */"
.B #include <unistd.h>
.P
.BI "int\~syscall(SYS_io_submit, aio_context_t\~" ctx_id ,
.BI "            long\~" n ", struct\~iocb\~*" iocbpp [ n ]);
.fi
.SH DESCRIPTION
.IR Note :
you probably want to use the
.BR io_setup (3)
wrapper function provided by
.IR libaio ;
see VERSIONS.
.P
The
.BR io_submit ()
system call
queues
.I n
I/O request blocks for processing in
the AIO context
.IR ctx_id .
The
.I iocbpp
argument should be an array of
.I n
AIO control blocks,
which will be submitted to context
.IR ctx_id .
.P
The
.I iocb
(I/O control block) structure defined in
.I linux/aio_abi.h
defines the parameters that control the I/O operation.
.P
.in +4n
.EX
#include <linux/aio_abi.h>
\&
struct iocb {
    __u64   aio_data;
    __u32   PADDED(aio_key, aio_rw_flags);
    __u16   aio_lio_opcode;
    __s16   aio_reqprio;
    __u32   aio_fildes;
    __u64   aio_buf;
    __u64   aio_nbytes;
    __s64   aio_offset;
    __u64   aio_reserved2;
    __u32   aio_flags;
    __u32   aio_resfd;
};
.EE
.in
.P
The fields of this structure are as follows:
.TP
.I aio_data
This data is copied into the
.I data
field of the
.I io_event
structure upon I/O completion (see
.BR io_getevents (2)).
.TP
.I aio_key
This is an internal field used by the kernel.
Do not modify this field after an
.BR io_submit ()
call.
.TP
.I aio_rw_flags
This defines the R/W flags passed with structure.
The valid values are:
.RS
.TP
.BR RWF_APPEND " (since Linux 4.16)"
.\" commit e1fc742e14e01d84d9693c4aca4ab23da65811fb
Append data to the end of the file.
See the description of the flag of the same name in
.BR pwritev2 (2)
as well as the description of
.B O_APPEND
in
.BR open (2).
The
.I aio_offset
field is ignored.
The file offset is not changed.
.TP
.BR RWF_DSYNC " (since Linux 4.13)"
Write operation complete according to requirement of
synchronized I/O data integrity.
See the description of the flag of the same name in
.BR pwritev2 (2)
as well the description of
.B O_DSYNC
in
.BR open (2).
.TP
.BR RWF_HIPRI " (since Linux 4.13)"
High priority request, poll if possible
.TP
.BR RWF_NOWAIT " (since Linux 4.14)"
Don't wait if the I/O will block for operations such as
file block allocations, dirty page flush, mutex locks,
or a congested block device inside the kernel.
If any of these conditions are met, the control block is returned
immediately with a return value of
.B \-EAGAIN
in the
.I res
field of the
.I io_event
structure (see
.BR io_getevents (2)).
.TP
.BR RWF_SYNC " (since Linux 4.13)"
Write operation complete according to requirement of
synchronized I/O file integrity.
See the description of the flag of the same name in
.BR pwritev2 (2)
as well the description of
.B O_SYNC
in
.BR open (2).
.TP
.BR RWF_NOAPPEND " (since Linux 6.9)"
Do not honor
.B O_APPEND
.BR open (2)
flag.
See the description of
.B RWF_NOAPPEND
in
.BR pwritev2 (2).
.TP
.BR RWF_ATOMIC " (since Linux 6.11)"
Write a block of data such that
a write will never be torn from power fail or similar.
See the description of
.B RWF_ATOMIC
in
.BR pwritev2 (2).
For usage with
.BR IOCB_CMD_PWRITEV ,
the upper vector limit is
.I stx_atomic_write_segments_max.
See
.B STATX_WRITE_ATOMIC
and
.I stx_atomic_write_segments_max
description
in
.BR statx (2).
.RE
.TP
.I aio_lio_opcode
This defines the type of I/O to be performed by the
.I iocb
structure.
The
valid values are defined by the enum defined in
.IR linux/aio_abi.h :
.IP
.in +4n
.EX
enum {
    IOCB_CMD_PREAD = 0,
    IOCB_CMD_PWRITE = 1,
    IOCB_CMD_FSYNC = 2,
    IOCB_CMD_FDSYNC = 3,
    IOCB_CMD_POLL = 5,
    IOCB_CMD_NOOP = 6,
    IOCB_CMD_PREADV = 7,
    IOCB_CMD_PWRITEV = 8,
};
.EE
.in
.TP
.I aio_reqprio
This defines the requests priority.
.TP
.I aio_fildes
The file descriptor on which the I/O operation is to be performed.
.TP
.I aio_buf
This is the buffer used to transfer data for a read or write operation.
.TP
.I aio_nbytes
This is the size of the buffer pointed to by
.IR aio_buf .
.TP
.I aio_offset
This is the file offset at which the I/O operation is to be performed.
.TP
.I aio_flags
This is the set of flags associated with the
.I iocb
structure.
The valid values are:
.RS
.TP
.B IOCB_FLAG_RESFD
Asynchronous I/O control must signal the file
descriptor mentioned in
.I aio_resfd
upon completion.
.TP
.BR IOCB_FLAG_IOPRIO " (since Linux 4.18)"
.\" commit d9a08a9e616beeccdbd0e7262b7225ffdfa49e92
Interpret the
.I aio_reqprio
field as an
.B IOPRIO_VALUE
as defined by
.IR linux/ioprio.h .
.RE
.TP
.I aio_resfd
The file descriptor to signal in the event of asynchronous I/O completion.
.SH RETURN VALUE
On success,
.BR io_submit ()
returns the number of
.IR iocb s
submitted
(which may be
less than
.IR n ,
or 0 if
.I n
is zero).
.P
On error,
\-1 is returned,
and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EAGAIN
Insufficient resources are available to queue any
.IR iocb s.
.TP
.B EBADF
The file descriptor specified in the first
.I iocb
is invalid.
.TP
.B EFAULT
One of the data structures points to invalid data.
.TP
.B EINVAL
The AIO context specified by
.I ctx_id
is invalid.
.TP
.B EINVAL
.I n
is less than 0.
.TP
.B EINVAL
The
.I iocb
at
.I *iocbpp[0]
is not properly initialized.
.TP
.B EINVAL
The operation specified is invalid for the file
descriptor in the
.IR iocb .
.TP
.B EINVAL
The value in the
.I aio_reqprio
field is invalid.
.TP
.B ENOSYS
.BR io_submit ()
is not implemented on this architecture.
.TP
.B EPERM
The
.I aio_reqprio
field is set with the class
.BR IOPRIO_CLASS_RT ,
but the submitting context does not have the
.B CAP_SYS_ADMIN
capability.
.SH VERSIONS
.UR https://pagure.io/libaio
.I libaio
.UE
provides a wrapper function with the same name,
but different prototype and return value.
You probably want to use that wrapper.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.5.
.SH SEE ALSO
.BR io_cancel (2),
.BR io_destroy (2),
.BR io_getevents (2),
.BR io_setup (2),
.BR io_submit (3),
.BR aio (7)
.\" .SH AUTHOR
.\" Kent Yoder.