Glue class member function with fuse API.

glue.hpp

#ifndef FUSE_GLUE_FUNCTION_HPP_
#define FUSE_GLUE_FUNCTION_HPP_

#include <functional>

#define DECL_GLUE_FUNC_(CONTEXT_TYPE, FUNCTION_NAME) \
template <typename T> struct glue_with_##FUNCTION_NAME; \
template <typename Ret, typename ...Arg> \
struct glue_with_##FUNCTION_NAME<Ret(*)(Arg...)> \
{ \
  static Ret f(Arg... arg) \
  { \
    return static_cast<CONTEXT_TYPE*>(fuse_get_context()->private_data)-> \
      FUNCTION_NAME(std::forward<Arg>(arg)...); \
  } \
};

#define GLUE_2(FROM, TO) &glue_with_##TO<decltype(fuse_operations::FROM)>::f
#define GLUE(NAME) &glue_with_##NAME<decltype(fuse_operations::NAME)>::f

#endif

OOFuse.cpp

#define FUSE_USE_VERSION 26

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include "glue.hpp"

struct hello_fs
{
  char const *hello_str;
  char const *hello_path;

  hello_fs() :
    hello_str("Hello World!\n"),
    hello_path("/hello")
    {}

  int getattr(const char *path, struct stat *stbuf)
  {
    int res = 0;

    memset(stbuf, 0, sizeof(struct stat));
    if (strcmp(path, "/") == 0) {
      stbuf->st_mode = S_IFDIR | 0755;
      stbuf->st_nlink = 2;
    } else if (strcmp(path, hello_path) == 0) {
      stbuf->st_mode = S_IFREG | 0444;
      stbuf->st_nlink = 1;
      stbuf->st_size = strlen(hello_str);
      //stbuf->st_size = 20;
    } else
      res = -ENOENT;

    return res;
  }

  int 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;

    filler(buf, ".", NULL, 0);
    filler(buf, "..", NULL, 0);
    filler(buf, hello_path + 1, NULL, 0);

    return 0;
  }

  int 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;
  }

  int 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);
    //sprintf(gbuf, "addr: %p\n", fuse_get_context()->private_data);
    //len = strlen(gbuf);
    if (offset < len) {
      if (offset + size > len)
        size = len - offset;
      memcpy(buf, hello_str + offset, size);
      //memcpy(buf, gbuf + offset, size);
    } else
      size = 0;

    return size;
  }
}; // hello_fs

DECL_GLUE_FUNC_(hello_fs, getattr)
DECL_GLUE_FUNC_(hello_fs, readdir)
DECL_GLUE_FUNC_(hello_fs, open)
DECL_GLUE_FUNC_(hello_fs, read)

static struct fuse_operations hello_oper = {
  .getattr        = GLUE(getattr),
  .readdir        = GLUE(readdir),
  .open           = GLUE(open),
  .read           = GLUE(read),
};


int main(int argc, char *argv[])
{
  hello_fs fs;
  return fuse_main(argc, argv, &hello_oper, (void*)&fs);
}