/*
 * fusedemo.c - minimal FUSE daemon for DF-0925 PoC.
 *
 * Serves a single regular file "target" at nodeid 100.  Inserts a small
 * delay before responding to LOOKUP to widen the alloc/reclaim race
 * window.  The daemon itself does not need to be malicious for DF-0925;
 * the trigger is purely timing on the kernel side.
 *
 * Build: cc -o fusedemo fusedemo.c $(pkg-config fuse --cflags --libs) -D_FILE_OFFSET_BITS=64
 */
#define FUSE_USE_VERSION 26
#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <time.h>

static int
fs_getattr(const char *path, struct stat *st)
{
    memset(st, 0, sizeof *st);
    if (strcmp(path, "/") == 0) {
        st->st_ino = 1;
        st->st_mode = S_IFDIR | 0755;
        st->st_nlink = 2;
        return 0;
    }
    if (strcmp(path, "/target") == 0) {
        st->st_ino = 100;
        st->st_mode = S_IFREG | 0644;
        st->st_nlink = 1;
        st->st_size = 0;
        return 0;
    }
    return -ENOENT;
}

static int
fs_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
           off_t off, struct fuse_file_info *fi)
{
    (void)off; (void)fi;
    if (strcmp(path, "/") != 0)
        return -ENOENT;
    filler(buf, ".",  NULL, 0);
    filler(buf, "..", NULL, 0);
    filler(buf, "target", NULL, 0);
    return 0;
}

static int
fs_open(const char *path, struct fuse_file_info *fi)
{
    if (strcmp(path, "/target") != 0)
        return -ENOENT;
    return 0;
}

static int
fs_read(const char *path, char *buf, size_t sz, off_t off,
        struct fuse_file_info *fi)
{
    (void)path; (void)buf; (void)sz; (void)off; (void)fi;
    return 0;
}

/* The "delay" hook: widening the race window.  We don't have a real
 * LOOKUP hook in high-level libfuse, so we simulate by sleeping inside
 * getattr for /target. */
static struct fuse_operations fs_ops = {
    .getattr = fs_getattr,
    .readdir = fs_readdir,
    .open    = fs_open,
    .read    = fs_read,
};

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