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IO_SUBMIT(2) Linux Programmer's Manual IO_SUBMIT(2)

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_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 4.7)
                   Write operation complete according to requirement of syn-
                   chronized I/O data integrity.  See the description of the
                   flag of the same name in pwritev2(2) as well the descrip-
                   tion of O_DSYNC in open(2).

            RWF_HIPRI (since Linux 4.6)
                   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 4.7)
                   Write operation complete according to requirement of syn-
                   chronized I/O file integrity.  See the description of the
                   flag of the same name in pwritev2(2) as well the descrip-
                   tion of O_SYNC in open(2).

     aio_lio_opcode
            This  defines the type of I/O to be performed by the iocb struc-
            ture.  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 per-
            formed.

     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 per-
            formed.

     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_con-
     text_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.