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hello_ll.c

/*
    FUSE: Filesystem in Userspace
    Copyright (C) 2001-2006  Miklos Szeredi <miklos@szeredi.hu>

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

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

#define FUSE_USE_VERSION 26

#include <fuse_lowlevel.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>

static const char *hello_str = "Hello World!\n";
static const char *hello_name = "hello";

static int hello_stat(fuse_ino_t ino, struct stat *stbuf)
{
    stbuf->st_ino = ino;
    switch (ino) {
    case 1:
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 2;
        break;

    case 2:
        stbuf->st_mode = S_IFREG | 0444;
        stbuf->st_nlink = 1;
        stbuf->st_size = strlen(hello_str);
        break;

    default:
        return -1;
    }
    return 0;
}

static void hello_ll_getattr(fuse_req_t req, fuse_ino_t ino,
                             struct fuse_file_info *fi)
{
    struct stat stbuf;

    (void) fi;

    memset(&stbuf, 0, sizeof(stbuf));
    if (hello_stat(ino, &stbuf) == -1)
        fuse_reply_err(req, ENOENT);
    else
        fuse_reply_attr(req, &stbuf, 1.0);
}

static void hello_ll_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
{
    struct fuse_entry_param e;

    if (parent != 1 || strcmp(name, hello_name) != 0)
        fuse_reply_err(req, ENOENT);
    else {
        memset(&e, 0, sizeof(e));
        e.ino = 2;
        e.attr_timeout = 1.0;
        e.entry_timeout = 1.0;
        hello_stat(e.ino, &e.attr);

        fuse_reply_entry(req, &e);
    }
}

struct dirbuf {
    char *p;
    size_t size;
};

static void dirbuf_add(fuse_req_t req, struct dirbuf *b, const char *name,
                       fuse_ino_t ino)
{
    struct stat stbuf;
    size_t oldsize = b->size;
    b->size += fuse_add_direntry(req, NULL, 0, name, NULL, 0);
    b->p = (char *) realloc(b->p, b->size);
    memset(&stbuf, 0, sizeof(stbuf));
    stbuf.st_ino = ino;
    fuse_add_direntry(req, b->p + oldsize, b->size - oldsize, name, &stbuf,
                      b->size);
}

#define min(x, y) ((x) < (y) ? (x) : (y))

static int reply_buf_limited(fuse_req_t req, const char *buf, size_t bufsize,
                             off_t off, size_t maxsize)
{
    if (off < bufsize)
        return fuse_reply_buf(req, buf + off, min(bufsize - off, maxsize));
    else
        return fuse_reply_buf(req, NULL, 0);
}

static void hello_ll_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
                             off_t off, struct fuse_file_info *fi)
{
    (void) fi;

    if (ino != 1)
        fuse_reply_err(req, ENOTDIR);
    else {
        struct dirbuf b;

        memset(&b, 0, sizeof(b));
        dirbuf_add(req, &b, ".", 1);
        dirbuf_add(req, &b, "..", 1);
        dirbuf_add(req, &b, hello_name, 2);
        reply_buf_limited(req, b.p, b.size, off, size);
        free(b.p);
    }
}

static void hello_ll_open(fuse_req_t req, fuse_ino_t ino,
                         struct fuse_file_info *fi)
{
    if (ino != 2)
        fuse_reply_err(req, EISDIR);
    else if ((fi->flags & 3) != O_RDONLY)
        fuse_reply_err(req, EACCES);
    else
        fuse_reply_open(req, fi);
}

static void hello_ll_read(fuse_req_t req, fuse_ino_t ino, size_t size,
                         off_t off, struct fuse_file_info *fi)
{
    (void) fi;

    assert(ino == 2);
    reply_buf_limited(req, hello_str, strlen(hello_str), off, size);
}

static struct fuse_lowlevel_ops hello_ll_oper = {
    .lookup     = hello_ll_lookup,
    .getattr      = hello_ll_getattr,
    .readdir    = hello_ll_readdir,
    .open       = hello_ll_open,
    .read   = hello_ll_read,
};

int main(int argc, char *argv[])
{
    struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
    struct fuse_chan *ch;
    char *mountpoint;
    int err = -1;

    if (fuse_parse_cmdline(&args, &mountpoint, NULL, NULL) != -1 &&
        (ch = fuse_mount(mountpoint, &args)) != NULL) {
        struct fuse_session *se;

        se = fuse_lowlevel_new(&args, &hello_ll_oper, sizeof(hello_ll_oper),
                               NULL);
        if (se != NULL) {
            if (fuse_set_signal_handlers(se) != -1) {
                fuse_session_add_chan(se, ch);
                err = fuse_session_loop(se);
                fuse_remove_signal_handlers(se);
                fuse_session_remove_chan(ch);
            }
            fuse_session_destroy(se);
        }
        fuse_unmount(mountpoint, ch);
    }
    fuse_opt_free_args(&args);

    return err ? 1 : 0;
}

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