在FreeBSD 用户空间与内核空间使用内存共享

最新推荐文章于 2023-05-19 08:50:10 发布

原创最新推荐文章于 2023-05-19 08:50:10 发布 · 2.2k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#freebsd #struct #module #makefile #null #cmd

本文介绍了一个在FreeBSD系统中创建的简单内存映射设备。该设备在内核空间分配了一块内存，并通过d_mmap接口将其暴露给用户空间应用程序。用户可以通过mmap系统调用将这块内存映射到进程的地址空间中，并进行读写操作。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

kernel创建一设备分配内存, 并将内存地址通过d_mmap 映射, userland使用mmap!

参考/sys/dev/mem/memdev.c.

FreeBSD 7.1

kernel 代码:

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/conf.h>
#include <sys/uio.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/priv.h>
#include <sys/disk.h>
#include <vm/vm.h>
#include <vm/pmap.h>

//#include <sys/bus.h>
//#include <machine/bus.h>

/* For use with destroy_dev(9). */
static struct cdev *memio_dev;

static d_write_t memio_write;
static d_ioctl_t memio_ioctl;
static d_read_t memio_read;
static d_mmap_t    memio_mmap;

#define MEMIO_MINOR    212

static struct cdevsw memio_cdevsw = {
    .d_version =    D_VERSION,
    .d_read =    memio_read,
    .d_write =    memio_write,
    .d_ioctl =    memio_ioctl,
    .d_mmap =    memio_mmap,
    .d_name =    "memio",
};

static void *zbuf;

static int
memio_read(struct cdev *dev __unused, struct uio *uio, int flags __unused)
{
    int error = 0;

    while (uio->uio_resid > 0 && error == 0)
        error = uiomove(zbuf, MIN(uio->uio_resid, PAGE_SIZE), uio);

    return error;
}
/* ARGSUSED */
static int
memio_write(struct cdev *dev __unused, struct uio *uio, int flags __unused)
{
    int error = 0;
    while( uio->uio_resid > 0 && error == 0 )
        error = uiomove(zbuf, MIN(uio->uio_resid, PAGE_SIZE), uio);
    return (0);
}

static int
memio_mmap(struct cdev *dev, vm_offset_t offset, vm_paddr_t *paddr,
        int prot __unused)
{
    *paddr = vtophys( zbuf );
    return (0);
}

/* ARGSUSED */
static int
memio_ioctl(struct cdev *dev __unused, u_long cmd, caddr_t data __unused,
    int flags __unused, struct thread *td)
{
    int error;

    if (cmd != DIOCSKERNELDUMP)
        return (ENOIOCTL);
    error = priv_check(td, PRIV_SETDUMPER);
    if (error)
        return (error);
    return (set_dumper(NULL));
}

/* ARGSUSED */
static int
memio_modevent(module_t mod __unused, int type, void *data __unused)
{
    switch(type) {
    case MOD_LOAD:
        if (bootverbose)
            printf("memio: <memio device>/n");
        zbuf = (void *)malloc(PAGE_SIZE, M_TEMP, M_WAITOK | M_ZERO);
        memcpy( zbuf, "hello from kernel", 18 );
        memio_dev = make_dev(&memio_cdevsw, MEMIO_MINOR, UID_ROOT,
            GID_WHEEL, 0666, "memio");
        uprintf( "load memio module./n" );
        break;

    case MOD_UNLOAD:
        destroy_dev(memio_dev);
        free(zbuf, M_TEMP);
        uprintf( "unload memio module./n" );
        break;

    case MOD_SHUTDOWN:
        break;

    default:
        return (EOPNOTSUPP);
    }

    return (0);
}

DEV_MODULE(memio, memio_modevent, NULL);
MODULE_VERSION(memio, 1);

Makefile

SRCS    = main.c
KMOD    = memio
KO      = $(KMOD).ko
KLDMOD = t

.include <bsd.kmod.mk>

userland test代码

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>

#define PAGE_SIZE 4096

int main ( int argc, char **argv )
{
    int configfd;
    configfd = open("/dev/memio", O_RDWR);
    if(configfd < 0) {
        perror("open");
        return -1;
    }

    char * address = NULL;
    address = mmap(NULL, PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, configfd, 0);
    if (address == MAP_FAILED) {
        perror("mmap");
        return -1;
    }

    printf("address=%p/n", address );
    printf("initial message: %s/n", address);
    memcpy(address + 11 , "*user*", 6);
    printf("changed message: %s/n", address);
    close(configfd);
    return 0;
}