io_submit(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       io_submit - submit asynchronous I/O blocks for processing

SYNOPSIS         top

       #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         top

       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         top

       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         top

       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 invalid 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         top

       The asynchronous I/O system calls first appeared in Linux 2.5.

CONFORMING TO         top

       io_submit() is Linux-specific and should not be used in programs
       that are intended to be portable.

NOTES         top

       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         top

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

COLOPHON         top

       This page is part of release 5.12 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                          2021-03-22                   IO_SUBMIT(2)

Pages that refer to this page: fcntl(2)io_cancel(2)io_destroy(2)io_getevents(2)io_setup(2)syscalls(2)systemd.exec(5)aio(7)