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A Straightforward Example

Example 2-2 modifies Example 2-1 to use contigmalloc and contigfree instead of malloc and free. Example 2-2 should clarify any misunderstandings you may have about contigmalloc and contigfree.

Note

To save space, the functions echo_open, echo_close, echo_write, and echo_read aren’t listed here, as they haven’t been changed.

Example 2-2. echo_contig.c

#include <sys/param.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/systm.h>

#include <sys/conf.h>
#include <sys/uio.h>
#include <sys/malloc.h>

#define BUFFER_SIZE     256

MALLOC_DEFINE(M_ECHO, "echo_buffer", "buffer for echo driver");

static d_open_t         echo_open;
static d_close_t        echo_close;
static d_read_t         echo_read;
static d_write_t        echo_write;

static struct cdevsw echo_cdevsw = {
        .d_version =    D_VERSION,
        .d_open =       echo_open,
        .d_close =      echo_close,
        .d_read =       echo_read,
        .d_write =      echo_write,
        .d_name =       "echo"
};

typedef struct echo {
        char buffer[BUFFER_SIZE];
        int length;
} echo_t;

static echo_t....