Ubuntu Manpage: io_submit - submit asynchronous I/O blocks for processing

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

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 is an internal field used by the kernel. Do not modify this field after an
io_submit(2) call.

aio_key
This is an internal field used by the kernel. Do not modify this field after an
io_submit(2) call.

aio_rw_flags
This defines the R/W flags passed with structure. The valid values are:

RWF_HIPRI
High priority request, poll if possible

RWF_DSYNC
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_SYNC
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).

RWF_NOWAIT
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)).

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_NOOP = 6,
IOCB_CMD_PREADV = 7,
IOCB_CMD_PWRITEV = 8,
};

aio_reqprio
This defines the requests priority.

aio_filedes
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 flag to be passed iocb structure. The only valid value is
IOCB_FLAG_RESFD, which indicates that the asynchronous I/O control must signal the
file descriptor mentioned in aio_resfd upon completion.

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, or the operation specified is invalid for
              the file descriptor in the iocb.

       ENOSYS io_submit() is not implemented on this architecture.

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 function 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.

COLOPHON

       This page is part of release 4.15 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/.