NAME
dmoverio
—
hardware-assisted data mover
interface
SYNOPSIS
pseudo-device dmoverio
#include
<dev/dmover/dmover_io.h>
DESCRIPTION
Thedmoverio
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).
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 perform other work while the
hardware-assisted data mover clears the specified 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 ALSO
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.