DMOVERIO(4) BSD Kernel Interfaces Manual DMOVERIO(4)NAMEdmoverio — hardware-assisted data mover interface
SYNOPSIS
pseudo-device dmoverio
#include <dev/dmover/dmover_io.h>
DESCRIPTION
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 pat‐
tern, 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 exam‐
ple, 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 pro‐
cessing 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).
EXAMPLES
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 per‐
form other work while the hardware-assisted data mover clears the speci‐
fied block of memory.
int
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) {
close(fd);
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)) {
close(fd);
return (-1);
}
/* Application can do other work here. */
if (read(fd, &resp, sizeof(resp)) != sizeof(resp)) {
close(fd);
return (-1);
}
if (resp.resp_id != req.req_id) {
close(fd);
return (-1);
}
if (resp.resp_error != 0) {
close(fd);
return (-1);
}
close(fd);
return (0);
}
SEE ALSOdmover(9)HISTORY
The dmoverio device first appeared in NetBSD 2.0.
AUTHORS
The dmoverio device was designed and implemented by Jason R. Thorpe
⟨thorpej@wasabisystems.com⟩ and contributed by Wasabi Systems, Inc.
BSD August 1, 2002 BSD
