io_submit

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_HIPRI
                     High priority request, poll if possible

              RWF_DSYNC
                     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_SYNC
                     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).

              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  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.

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

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/.

Linux                             2017-09-15                      IO_SUBMIT(2)
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