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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
       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  in‐
              valid 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)

Linux                                                                          2021-03-22                                                                   IO_SUBMIT(2)