Re: [fuse-devel] adding the fields for struct fuse in fuse.h

[Steve H. <fus...@nt...>]

Miklos,

The problem is in the fact that the function pointers in fuse_operations
can only be set to point to *static* members of a C++ object, so in the
case of the init function we would have something like:

class c_t {
    static void *op_init(void) {
    }

    void set_fuse_ops() {
	struct fuse_operations fuse_ops = {....
        	                           op_init,
                	                   ... };
    }
};

But op_init is static and hence it cannot get any information about the
object pointer for the instance of c_t from which set_fuse_ops is being
called. Hence I cannot define op_init such that it returns the object
pointer. The only way I could see around this is if I can access struct
fuse and set the user_data directly, as follows:

class c_t {
    struct fuse* fuse_instance;

    void set_fuse_ops() {
        struct fuse_operations fuse_ops = {...};
        fuse_instance = fuse_new(...);
	fuse_instance->user_data = this;
    }
};

Then to get the object pointer I do:

    fuse_context *fc = fuse_get_context();
    if (fc) return static_cast<c_t*>(fc->fuse->user_data);

The only issue is that I have to modify struct fuse to make user_data
visible.

Is there any other way of doing this without having to expose hidden
fields in struct fuse?

Thanks,
Steve

Miklos Szeredi wrote:
>>The reason for this request is that I want to associate each fuse
>>instance with a c++ object, such that I can have access to methods in
>>the c++ object from within the statically FUSE file operation functions.
>>The way I have done this is to set the fuse.user_data field to the
>>object self pointer, and then I can access that pointer from within the
>>static functions. This works fine except that I have to explicitly
>>modify fuse.h so that the contents of the fuse structure are exposed in
>>fuse.h. Is there any way of incorporating this so I don't have to modify
>> fuse.h?
> 
> 
> Yes:
> 
>  - return object pointer from init() method.
> 
>  - retreive object pointer with 'fuse_get_context()->private_data'
> 
> Miklos
>