Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

DMOVERIO(4)                  Device Drivers Manual                 DMOVERIO(4)

     dmoverio - hardware-assisted data mover interface

     pseudo-device dmoverio

     #include <dev/dmover/dmover_io.h>

     The dmoverio pseudo-device driver provides an interface to hardware-
     assisted data movers, which the kernel supports using the dmover(9)
     facility.  This can be used to copy data from one location in memory to
     another, clear a region of memory, fill a region of memory with a
     pattern, and perform simple operations on multiple regions of memory,
     such as an XOR, without intervention by the CPU.

     A dmoverio function always has one output region.  A function may have
     zero or more input regions, or may use an immediate value as an input.
     For functions which use input regions, the lengths of each input region
     and the output region must be the same.  All dmoverio functions with the
     same name will have the same number of and type inputs.

     To use dmoverio, the client must first create a session.  This is
     achieved by performing the following steps:

        Create a session handle by opening the /dev/dmoverio device.

        Select the dmoverio function using the DMIO_SETFUNC ioctl, which
         takes the following argument:

               #define DMIO_MAX_FUNCNAME     64
               struct dmio_setfunc {
                       char dsf_name[DMIO_MAX_FUNCNAME];

         If the specified function is not available, the DMIO_SETFUNC ioctl
         will fail with an error code of ESRCH.

     To submit a request for processing the following steps must be performed:

        Fill in a request structure:

               typedef struct {
                       struct iovec *dmbuf_iov;
                       u_int dmbuf_iovcnt;
               } dmio_buffer;

               struct dmio_usrreq {
                       /* Output buffer. */
                       dmio_buffer req_outbuf;

                       /* Input buffer. */
                       union {
                               uint8_t _immediate[8];
                               dmio_buffer *_inbuf;
                       } _req_inbuf_un;

               #define req_immediate           _req_inbuf_un._immediate
               #define req_inbuf               _req_inbuf_un._inbuf

                       uint32_t req_id;        /* request ID; passed in response */

         For functions which use an immediate value as an input, the
         req_immediate member is used to specify the value.  Values smaller
         than 8 bytes should use the least-significant bytes first.  For
         example, a 32-bit integer would occupy bytes 0, 1, 2, and 3.

         For functions which use input regions, req_inbuf should point to an
         array of dmio_buffer's.

         The req_id should be a unique value for each request submitted by the
         client.  It will be passed back unchanged in the response when
         processing of the request has completed.

        Write the request structure to the session handle using the write(2)
         system call.  Multiple requests may be written to the session in a
         single call.

        Read the response structure back from the session handle using the
         read(2) system call.  The response structure is defined as follows:

               struct dmio_usrresp {
                       uint32_t resp_id;
                       int resp_error;

         The resp_id corresponds to the req_id in the request.  resp_error
         contains 0 if the request succeeded or an errno(2) value indicating
         why the request failed.  Multiple responses may be read back in a
         single call.  Note that responses may not be received in the same
         order as requests were written.

     When a client is finished using a dmoverio session, the session is
     destroyed by closing the session handle using close(2).

     The following is an example of a client using dmoverio to zero-fill a
     region of memory.  In this example, the application would be able to
     perform other work while the hardware-assisted data mover clears the
     specified block of memory.

     hw_bzero(void *buf, size_t len)
             static uint32_t reqid;

             struct dmio_setfunc dsf;
             struct iovec iov;
             struct dmio_usrreq req;
             struct dmio_usrresp resp;
             int fd;

             fd = open("/dev/dmoverio", O_RDWR, 0666);
             if (fd == -1)
                     return (-1);

             strcpy(dsf.dsf_name, "zero");

             if (ioctl(fd, DMIO_SETFUNC, &dsf) == -1) {
                     return (-1);

             iov.iov_base = buf;
             iov.iov_len = len;

             req.req_outbuf.dmbuf_iov = &iov;
             req.req_outbuf.dmbuf_iovcnt = 1;
             req.req_id = reqid++;

             if (write(fd, &req, sizeof(req)) != sizeof(req)) {
                     return (-1);

             /* Application can do other work here. */

             if (read(fd, &resp, sizeof(resp)) != sizeof(resp)) {
                     return (-1);

             if (resp.resp_id != req.req_id) {
                     return (-1);

             if (resp.resp_error != 0) {
                     return (-1);

             return (0);


     The dmoverio device first appeared in NetBSD 2.0.

     The dmoverio device was designed and implemented by Jason R. Thorpe
     <thorpej@wasabisystems.com> and contributed by Wasabi Systems, Inc.

NetBSD 10.99                    August 1, 2002                    NetBSD 10.99