io_submit(2)

NAME
io_submit - submit asynchronous I/O blocks for processing

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <linux/aio_abi.h>
#include <sys/syscall.h>    /* Definition of SYS_* constants */
#include <unistd.h>

int syscall(SYS_io_submit, aio_context_t ctx_id,
            long n, struct iocb *iocbpp[n]);

DESCRIPTION
Note: you probably want to use the io_setup(3) wrapper function provided by libaio; see VERSIONS.

The io_submit() system call queues n I/O request blocks for processing in the AIO context ctx_id. The iocbpp argument should be an array of n 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).

    RWF_NOAPPEND (since Linux 6.9)
        Do not honor O_APPEND open(2) flag. See the description of RWF_NOAPPEND in pwritev2(2).

    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 RWF_ATOMIC in pwritev2(2). For usage with IOCB_CMD_PWRITEV, the upper vector limit is stx_atomic_write_segments_max. See STATX_WRITE_ATOMIC and stx_atomic_write_segments_max description in statx(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 n, or 0 if n is zero).

On error, -1 is returned, and errno is set to indicate the error.

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.

EINVAL
    n is less than 0.

EINVAL
    The iocb at *iocbpp[0] is not properly initialized.

EINVAL
    The operation specified is invalid for the file descriptor in the iocb.

EINVAL
    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
libaio (https://pagure.io/libaio) provides a wrapper function with the same name, but different prototype and return value. You probably want to use that wrapper.

STANDARDS
Linux.

HISTORY
Linux 2.5.

SEE ALSO
io_cancel(2), io_destroy(2), io_getevents(2), io_setup(2), io_submit(3), aio(7)