hello.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
  heavily modified by Jann Horn <jannh@google.com>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.

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

#define FUSE_USE_VERSION 26

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <err.h>
#include <sys/uio.h>

static const char *hello_path = "/hello";

static char data_state[sizeof(struct iovec)];

static int hello_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 | 0666;
        stbuf->st_nlink = 1;
        stbuf->st_size = sizeof(data_state);
        stbuf->st_blocks = 0;
    } else
        res = -ENOENT;
    return res;
}

static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler, off_t offset, struct fuse_file_info *fi) {
    filler(buf, ".", NULL, 0);
    filler(buf, "..", NULL, 0);
    filler(buf, hello_path + 1, NULL, 0);
    return 0;
}

static int hello_open(const char *path, struct fuse_file_info *fi) {
    return 0;
}

static int hello_read(const char *path, char *buf, size_t size, off_t offset, struct fuse_file_info *fi) {
    sleep(10);
    size_t len = sizeof(data_state);
    if (offset < len) {
        if (offset + size > len)
            size = len - offset;
        memcpy(buf, data_state + offset, size);
    } else
        size = 0;
    return size;
}

static int hello_write(const char *path, const char *buf, size_t size, off_t offset, struct fuse_file_info *fi) {
    if (offset != 0)
        errx(1, "got write with nonzero offset");
    if (size != sizeof(data_state))
        errx(1, "got write with size %d", (int)size);
    memcpy(data_state + offset, buf, size);
    return size;
}

static struct fuse_operations hello_oper = {
    .getattr    = hello_getattr,
    .readdir    = hello_readdir,
    .open       = hello_open,
    .read       = hello_read,
    .write      = hello_write,
};

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