FUSE API 的两种使用方法

refer: http://blog.csdn.net/langeldep/article/details/6401567
FUSE 虚拟文件系统集成到我们的应用程序时，有两种使用策略，一种是使用比较上层的API，

主循环我们只能调用 ret = fuse_main (fargc, fargv, &my_handler, NULL) 这个主循环的接口，

my_handler我们只取我们关心API属性，如下所示

[cpp]
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static struct fuse_operations my_handler =
{
.getattr = xmp_getattr,
.opendir = xmp_opendir,
.readdir = xmp_readdir,
.mkdir = xmp_mkdir,
.unlink = xmp_unlink,
.rmdir = xmp_rmdir,
.rename = xmp_rename,
.link = xmp_link,
.truncate = xmp_truncate,
.create = xmp_create,
.open = xmp_open,
.read = xmp_read,
.write = xmp_write,
.flush = xmp_flush,
.release = xmp_release,
};

然后我们自己要来实现上面的各种 xmp_ 开头的函数。

还有一种是使用 fuse_session_loop 这个比较底层的函数来实现，这个时候我们要实现的API都是一些比较底层

的API, 比如下面的代码所示 ：

[c-sharp]
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static struct fuse_lowlevel_ops lowlevel_handler =
{
.lookup = lowlevel_lookup,
.getattr = lowlevel_getattr,
.readdir = lowlevel_readdir,
.mkdir = lowlevel_mkdir,
.rmdir = lowlevel_rmdir,
.open = lowlevel_open,
.read = lowlevel_read,
.write = lowlevel_write,
.unlink = lowlevel_unlink,
.rename = lowlevel_rename,
};

具体的使用方法如下 ：

[c-sharp]
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struct fuse_chan *ch;

fargc = 3;
fargv[0] = g_Config.processName;
fargv[1] = g_Config.mountSource;
fargv[2] = g_Config.mountPath;
struct fuse_args args = FUSE_ARGS_INIT(fargc, fargv);

snprintf (buf, sizeof(buf)-1, "umount -l %s", g_Config.mountPath);
system(buf);
ret = fuse_parse_cmdline(&args, &g_Config.mountPath, NULL, NULL);
ch = fuse_mount(g_Config.mountPath, &args);
if (ret == -1 || ch == NULL)
{
fprintf (stderr, "fuse mout fail/n");
exit(1);
}
struct fuse_session *se;
se = fuse_lowlevel_new(&args, &lowlevel_handler, sizeof(lowlevel_handler), NULL);
if (se != NULL)
{
if (fuse_set_signal_handlers(se) != -1)
{
fuse_session_add_chan(se, ch);
ret = fuse_session_loop(se);
fuse_remove_signal_handlers(se);
fuse_session_remove_chan(ch);
}
fuse_session_destroy(se);
}
fuse_unmount(g_Config.mountPath, ch);
fuse_opt_free_args(&args);;

底层的API使用起来相对灵活性大一点，本人推荐使用底层的API。当然了，上层的API使用起来相对简单一点。

下面复制了一个具体的底层API的实现，供大家参考。

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void lowlevel_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
{
writelog (LOG_DEBUG, "call user function_______%s______fuse_ino_t = %d", __FUNCTION__, ino);
if (ino != 2)
fuse_reply_err(req, EISDIR);
else if ((fi->flags & 3) != O_RDONLY)
fuse_reply_err(req, EACCES);
else
{
/* direct_io is supposed to allow partial reads. However, setting
* the flag causes read length max at 4096 bytes which leads to
* *many* requests, poor performance, and errors. Some resources
* like TCP ports are recycled too fast for Linux to cope.
*/
//fi->direct_io = 1;
fuse_reply_open(req, fi);
}
}

另外在使用fuse的时候，要注意的是 struct fuse_file_info *fi 这个结构体数据的填充，

其中最关键的是 direct_io 和 nonseekable。

具体如下 ：

fi->fh = socket(PF_INET, SOCK_STREAM, 0);

fi->direct_io = 1;

fi->nonseekable = 0;

设置了direct_io=1 可以提高文件读写的速度，一次IO的大小就不在局限于4K,

设置 nonseekable=0, 上层的应用才可以调用seek函数进行，否则无法seek。

这两个地方时很关键的。