IO_SUBMIT
Section: Linux Programmer's Manual (2)
Updated: 2021-03-22
Index
Return to Main Contents
NAME
io_submit - submit asynchronous I/O blocks for processing
SYNOPSIS
#include <linux/aio_abi.h> /* Defines needed types */
int io_submit(aio_context_t ctx_id, long nr, struct iocb **iocbpp);
Note:
There is no glibc wrapper for this system call; see NOTES.
DESCRIPTION
Note:
this page describes the raw Linux system call interface.
The wrapper function provided by
libaio
uses a different type for the
ctx_id
argument.
See NOTES.
The
io_submit()
system call
queues nr I/O request blocks for processing in
the AIO context ctx_id.
The
iocbpp
argument should be an array of nr AIO control blocks,
which will be submitted to context ctx_id.
The
iocb
(I/O control block) structure defined in
linux/aio_abi.h
defines the parameters that control the I/O operation.
#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;
};
The fields of this structure are as follows:
- aio_data
-
This data is copied into the
data
field of the
io_event
structure upon I/O completion (see
io_getevents(2)).
- aio_key
-
This is an internal field used by the kernel.
Do not modify this field after an
io_submit()
call.
- aio_rw_flags
-
This defines the R/W flags passed with structure.
The valid values are:
-
- RWF_APPEND (since Linux 4.16)
-
Append data to the end of the file.
See the description of the flag of the same name in
pwritev2(2)
as well as the description of
O_APPEND
in
open(2).
The
aio_offset
field is ignored.
The file offset is not changed.
- 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
pwritev2(2)
as well the description of
O_DSYNC
in
open(2).
- RWF_HIPRI (since Linux 4.13)
-
High priority request, poll if possible
- 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
-EAGAIN
in the
res
field of the
io_event
structure (see
io_getevents(2)).
- 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
pwritev2(2)
as well the description of
O_SYNC
in
open(2).
- aio_lio_opcode
-
This defines the type of I/O to be performed by the
iocb
structure.
The
valid values are defined by the enum defined in
linux/aio_abi.h:
-
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,
};
- aio_reqprio
-
This defines the requests priority.
- aio_fildes
-
The file descriptor on which the I/O operation is to be performed.
- aio_buf
-
This is the buffer used to transfer data for a read or write operation.
- aio_nbytes
-
This is the size of the buffer pointed to by
aio_buf.
- aio_offset
-
This is the file offset at which the I/O operation is to be performed.
- aio_flags
-
This is the set of flags associated with the
iocb
structure.
The valid values are:
-
- IOCB_FLAG_RESFD
-
Asynchronous I/O control must signal the file
descriptor mentioned in
aio_resfd
upon completion.
- IOCB_FLAG_IOPRIO (since Linux 4.18)
-
Interpret the
aio_reqprio
field as an
IOPRIO_VALUE
as defined by
linux/ioprio.h.
- aio_resfd
-
The file descriptor to signal in the event of asynchronous I/O completion.
RETURN VALUE
On success,
io_submit()
returns the number of iocbs submitted (which may be
less than nr, or 0 if nr is zero).
For the failure return, see NOTES.
ERRORS
- EAGAIN
-
Insufficient resources are available to queue any iocbs.
- EBADF
-
The file descriptor specified in the first iocb is invalid.
- EFAULT
-
One of the data structures points to invalid data.
- EINVAL
-
The AIO context specified by ctx_id is invalid.
nr is less than 0.
The iocb at
*iocbpp[0]
is not properly initialized, the operation specified is invalid for the file
descriptor in the iocb, or the value in the
aio_reqprio
field is invalid.
- ENOSYS
-
io_submit()
is not implemented on this architecture.
- EPERM
-
The
aio_reqprio
field is set with the class
IOPRIO_CLASS_RT,
but the submitting context does not have the
CAP_SYS_ADMIN
capability.
VERSIONS
The asynchronous I/O system calls first appeared in Linux 2.5.
CONFORMING TO
io_submit()
is Linux-specific and should not be used in
programs that are intended to be portable.
NOTES
Glibc does not provide a wrapper for this system call.
You could invoke it using
syscall(2).
But instead, you probably want to use the
io_submit()
wrapper function provided by
libaio.
Note that the
libaio
wrapper function uses a different type
(io_context_t)
for the
ctx_id
argument.
Note also that the
libaio
wrapper does not follow the usual C library conventions for indicating errors:
on error it returns a negated error number
(the negative of one of the values listed in ERRORS).
If the system call is invoked via
syscall(2),
then the return value follows the usual conventions for
indicating an error: -1, with
errno
set to a (positive) value that indicates the error.
SEE ALSO
io_cancel(2),
io_destroy(2),
io_getevents(2),
io_setup(2),
aio(7)
COLOPHON
This page is part of release 5.11 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
This document was created by
man2html,
using the manual pages.
Time: 06:22:44 GMT, May 09, 2021