FUSE:用户空间文件系统,Ubuntu和openwrt下测试成功

1. 下载安装
wget
tar zxvf fuse-2.9.1.tar.gz
cd fuse-2.9.1
./configure
make
sudo make install

2. 测试代码

/*--------------------------------------------------------------------------------------------
gcc -Wall -O2 hello.c -o hello `pkg-config fuse --cflags --libs`

mkdir /tmp/fuse             //在/tmp下建立fuse目录，用于挂载hello文件系统
./hello /tmp/fuse         //挂载hello文件系统
ls -l /tmp/fuse            //执行ls时，会调用到readdir函数，该函数会添加一个hello文件
    -r--r--r-- 1 root root 13 1970-01-01 07:00 hello
cat /tmp/fuse/hello    //执行cat      字符串hello_str中的内容读出
fusermount -u /tmp/fuse //卸载hello文件系统
---------------------------------------------------------------------------------------------*/
#define FUSE_USE_VERSION 26    //先定义, fuse.h中有判断

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

static const char *hello_str = "Hello World!\n";
static const char *hello_path = "/hello";

//该函数与stat()类似，用于得到文件的属性，将其存入到结构体struct stat中
static int hello_getattr(const char *path, struct stat *stbuf)
{
    int res = 0;

    memset(stbuf, 0, sizeof(struct stat));    //用于初始化结构体stat
    if (strcmp(path, "/") == 0) {
        stbuf->st_mode = S_IFDIR | 0755;    //S_IFDIR 用于说明/为目录，详见S_IFDIR定义
        stbuf->st_nlink = 2;    //文件链接数
    } else if (strcmp(path, hello_path) == 0) {
        stbuf->st_mode = S_IFREG | 0444;    //S_IFREG用于说明/hello为常规文件
        stbuf->st_nlink = 1;
        stbuf->st_size = strlen(hello_str);    //设置文件长度为hello_str的长度
    } else
        res = -ENOENT;    //返回错误信息，没有该文件或目录

    return res;    //执行成功返回0
}

//该函数用于读取目录中的内容，并在/目录下增加了. .. hello三个目录项
static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
             off_t offset, struct fuse_file_info *fi)
{
    (void) offset;
    (void) fi;

    if (strcmp(path, "/") != 0)
        return -ENOENT;

    /* fill, 其作用是在readdir函数中增加一个目录项
    typedef int (*fuse_fill_dir_t) (void *buf, const char *name,
        const struct stat *stbuf, off_t off);
    */
    filler(buf, ".", NULL, 0);
    filler(buf, "..", NULL, 0);
    filler(buf, hello_path + 1, NULL, 0);    //指针+1(/hello), 即增加 hello 目录项

    return 0;
}

//打开文件
static int hello_open(const char *path, struct fuse_file_info *fi)
{
    if (strcmp(path, hello_path) != 0)
        return -ENOENT;

    if ((fi->flags & 3) != O_RDONLY)
        return -EACCES;

    return 0;
}

//读文件
static int hello_read(const char *path, char *buf, size_t size, off_t offset,
              struct fuse_file_info *fi)
{
    size_t len;
    (void) fi;
    if(strcmp(path, hello_path) != 0)
        return -ENOENT;

    len = strlen(hello_str);
    if (offset < len) {
        if (offset + size > len)
            size = len - offset;
        memcpy(buf, hello_str + offset, size);
    } else
        size = 0;

    return size;
}

//注册自定义函数
static struct fuse_operations hello_oper = {
    .getattr    = hello_getattr,
    .readdir    = hello_readdir,
    .open        = hello_open,
    .read        = hello_read,
};

//只需调用fuse_main()，剩下的事就交给FUSE了*
int main(int argc, char *argv[])
{
    return fuse_main(argc, argv, &hello_oper, NULL);
}

3.Makefile

OPENWRT = 1

ifeq ($(OPENWRT), 1)
    CC = ~/OpenWrt-SDK-ar71xx-for-linux-i486-gcc-4.6-linaro_uClibc-0.9.33.2/staging_dir/toolchain-mips_r2_gcc-4.6-linaro_uClibc-0.9.33.2/bin/mips-openwrt-linux-gcc
    CFLAGS += -I ~/openwrt-lib/include -L ~/openwrt-lib/lib

else
    CC = gcc
endif

CFLAGS += -Wall -O2
#CFLAGS += -g

#可执行文件名和相关的obj文件
APP_BINARY = hello_fuse
SRCS += hello.c
OBJS += hello.o

all: APP_FILE

hello.o:
    $(CC) $(CFLAGS) -c $(SRCS) `pkg-config fuse --cflags --libs`

APP_FILE: $(OBJS)
    $(CC) $(CFLAGS) $(OBJS) -o $(APP_BINARY) $(LFLAGS) `pkg-config fuse --cflags --libs`

.PHONY: clean
clean:
    @echo "cleanning project"
    $(RM) *.a *.o *~ *.so *.lo $(APP_BINARY)
    @echo "clean completed"

测试过程:
$mkdir /tmp/fuse

$./hello /tmp/fuse

$ls -l /tmp/fuse
    -r--r--r--  1 root root 13 Jan  1  1970 hello

$cat /tmp/fuse/hello
    Hello World!

$fusermount -u /tmp/fuse