notify_store_retrieve.c

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/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2016 Nikolaus Rath <Nikolaus@rath.org>
 
  This program can be distributed under the terms of the GNU GPLv2.
  See the file GPL2.txt.
*/

 
#define FUSE_USE_VERSION FUSE_MAKE_VERSION(3, 12)
 
#include <fuse_lowlevel.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <assert.h>
#include <stddef.h>
#include <unistd.h>
#include <pthread.h>
#include <stdbool.h>
 
/* We can't actually tell the kernel that there is no
   timeout, so we just send a big value */
#define NO_TIMEOUT 500000
 
#define MAX_STR_LEN 128
#define FILE_INO 2
#define FILE_NAME "current_time"
static char file_contents[MAX_STR_LEN];
static int lookup_cnt = 0;
static int open_cnt = 0;
static size_t file_size;
static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
 
/* Keep track if we ever stored data (==1), and
   received it back correctly (==2) */
static int retrieve_status = 0;
 
static bool is_umount = false;
 
/* updater thread tid */
static pthread_t updater;
 
/* Command line parsing */
struct options {
        int no_notify;
        int update_interval;
};
static struct options options = {
        .no_notify = 0,
        .update_interval = 1,
};
 
#define OPTION(t, p) { t, offsetof(struct options, p), 1 }
static const struct fuse_opt option_spec[] = {
        OPTION("--no-notify", no_notify),
        OPTION("--update-interval=%d", update_interval), FUSE_OPT_END
};
 
static int tfs_stat(fuse_ino_t ino, struct stat *stbuf)
{
        stbuf->st_ino = ino;
        if (ino == FUSE_ROOT_ID) {
                stbuf->st_mode = S_IFDIR | 0755;
                stbuf->st_nlink = 1;
        }
 
        else if (ino == FILE_INO) {
                stbuf->st_mode = S_IFREG | 0444;
                stbuf->st_nlink = 1;
                stbuf->st_size = file_size;
        }
 
        else
                return -1;
 
        return 0;
}
 
static void tfs_init(void *userdata, struct fuse_conn_info *conn)
{
        (void)userdata;
 
        /* Disable the receiving and processing of FUSE_INTERRUPT requests */
        conn->no_interrupt = 1;
}
 
static void tfs_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)
{
        struct fuse_entry_param e;
        memset(&e, 0, sizeof(e));
 
        if (parent != FUSE_ROOT_ID)
                goto err_out;
        else if (strcmp(name, FILE_NAME) == 0)
                e.ino = FILE_INO;
        else
                goto err_out;
 
        e.attr_timeout = NO_TIMEOUT;
        e.entry_timeout = NO_TIMEOUT;
        if (tfs_stat(e.ino, &e.attr) != 0)
                goto err_out;
        fuse_reply_entry(req, &e);
 
        /*
     * must only be set when the kernel knows about the entry,
     * otherwise update_fs_loop() might see a positive count, but kernel
     * would not have the entry yet
     */
        if (e.ino == FILE_INO) {
                pthread_mutex_lock(&lock);
                lookup_cnt++;
                pthread_mutex_unlock(&lock);
        }
 
        return;
 
err_out:
        fuse_reply_err(req, ENOENT);
}
 
static void tfs_forget(fuse_req_t req, fuse_ino_t ino, uint64_t nlookup)
{
        (void)req;
        if (ino == FILE_INO) {
                pthread_mutex_lock(&lock);
                lookup_cnt -= nlookup;
                pthread_mutex_unlock(&lock);
        } else
                assert(ino == FUSE_ROOT_ID);
        fuse_reply_none(req);
}
 
static void tfs_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 (tfs_stat(ino, &stbuf) != 0)
                fuse_reply_err(req, ENOENT);
        else
                fuse_reply_attr(req, &stbuf, NO_TIMEOUT);
}
 
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 tfs_readdir(fuse_req_t req, fuse_ino_t ino, size_t size, off_t off,
                        struct fuse_file_info *fi)
{
        (void)fi;
 
        if (ino != FUSE_ROOT_ID)
                fuse_reply_err(req, ENOTDIR);
        else {
                struct dirbuf b;
 
                memset(&b, 0, sizeof(b));
                dirbuf_add(req, &b, FILE_NAME, FILE_INO);
                reply_buf_limited(req, b.p, b.size, off, size);
                free(b.p);
        }
}
 
static void tfs_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
{
        /* Make cache persistent even if file is closed,
       this makes it easier to see the effects */
        fi->keep_cache = 1;
 
        if (ino == FUSE_ROOT_ID)
                fuse_reply_err(req, EISDIR);
        else if ((fi->flags & O_ACCMODE) != O_RDONLY)
                fuse_reply_err(req, EACCES);
        else if (ino == FILE_INO) {
                fuse_reply_open(req, fi);
                pthread_mutex_lock(&lock);
                open_cnt++;
                pthread_mutex_unlock(&lock);
        } else {
                // This should not happen
                fprintf(stderr, "Got open for non-existing inode!\n");
                fuse_reply_err(req, ENOENT);
        }
}
 
static void tfs_read(fuse_req_t req, fuse_ino_t ino, size_t size, off_t off,
                     struct fuse_file_info *fi)
{
        (void)fi;
 
        assert(ino == FILE_INO);
        reply_buf_limited(req, file_contents, file_size, off, size);
}
 
static void tfs_retrieve_reply(fuse_req_t req, void *cookie, fuse_ino_t ino,
                               off_t offset, struct fuse_bufvec *data)
{
        struct fuse_bufvec bufv;
        char buf[MAX_STR_LEN];
        char *expected;
        ssize_t ret;
 
        assert(ino == FILE_INO);
        assert(offset == 0);
        expected = (char *)cookie;
 
        bufv.count = 1;
        bufv.idx = 0;
        bufv.off = 0;
        bufv.buf[0].size = MAX_STR_LEN;
        bufv.buf[0].mem = buf;
        bufv.buf[0].flags = 0;
 
        ret = fuse_buf_copy(&bufv, data, 0);
        assert(ret > 0);
        assert(strncmp(buf, expected, ret) == 0);
        free(expected);
        retrieve_status = 2;
        fuse_reply_none(req);
}
 
static void tfs_destroy(void *userdata)
{
        (void)userdata;
 
        is_umount = true;
 
        pthread_join(updater, NULL);
}
 
static const struct fuse_lowlevel_ops tfs_oper = {
        .init = tfs_init,
        .lookup = tfs_lookup,
        .getattr = tfs_getattr,
        .readdir = tfs_readdir,
        .open = tfs_open,
        .read = tfs_read,
        .forget = tfs_forget,
        .retrieve_reply = tfs_retrieve_reply,
        .destroy = tfs_destroy,
};
 
static void update_fs(void)
{
        struct tm tmbuf;
        struct tm *now;
        time_t t;
        t = time(NULL);
        now = localtime_r(&t, &tmbuf);
        assert(now != NULL);
 
        file_size = strftime(file_contents, MAX_STR_LEN,
                             "The current time is %H:%M:%S\n", now);
        assert(file_size != 0);
}
 
static void *update_fs_loop(void *data)
{
        struct fuse_session *se = (struct fuse_session *)data;
        struct fuse_bufvec bufv;
        int ret;
 
        while (!is_umount) {
                update_fs();
                pthread_mutex_lock(&lock);
                if (!options.no_notify && open_cnt && lookup_cnt) {
                        /* Only send notification if the kernel
               is aware of the inode */
                        bufv.count = 1;
                        bufv.idx = 0;
                        bufv.off = 0;
                        bufv.buf[0].size = file_size;
                        bufv.buf[0].mem = file_contents;
                        bufv.buf[0].flags = 0;
 
                        /*
             * Some errors (ENOENT, EBADF, ENODEV) have to be accepted as they
             * might come up during umount, when kernel side already releases
             * all inodes, but does not send FUSE_DESTROY yet.
             */
 
                        ret = fuse_lowlevel_notify_store(se, FILE_INO, 0, &bufv,
                                                         0);
                        if ((ret != 0 && !is_umount) && ret != -ENOENT &&
                            ret != -EBADF && ret != -ENODEV) {
                                fprintf(stderr,
                                        "ERROR: fuse_lowlevel_notify_store() failed with %s (%d)\n",
                                        strerror(-ret), -ret);
                                abort();
                        }
 
                        /* To make sure that everything worked correctly, ask the
               kernel to send us back the stored data */
                        ret = fuse_lowlevel_notify_retrieve(
                                se, FILE_INO, MAX_STR_LEN, 0,
                                (void *)strdup(file_contents));
                        assert((ret == 0 || is_umount) || ret == -ENOENT ||
                               ret == -EBADF || ret != -ENODEV);
                        if (retrieve_status == 0)
                                retrieve_status = 1;
                }
                pthread_mutex_unlock(&lock);
                sleep(options.update_interval);
        }
        return NULL;
}
 
static void show_help(const char *progname)
{
        printf("usage: %s [options] <mountpoint>\n\n", progname);
        printf("File-system specific options:\n"
               "    --update-interval=<secs>  Update-rate of file system contents\n"
               "    --no-notify            Disable kernel notifications\n"
               "\n");
}
 
int main(int argc, char *argv[])
{
        struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
        struct fuse_session *se;
        struct fuse_cmdline_opts opts;
        struct fuse_loop_config *config;
        int ret = -1;
 
        if (fuse_opt_parse(&args, &options, option_spec, NULL) == -1)
                return 1;
 
        if (fuse_parse_cmdline(&args, &opts) != 0)
                return 1;
        if (opts.show_help) {
                show_help(argv[0]);
                fuse_cmdline_help();
                fuse_lowlevel_help();
                ret = 0;
                goto err_out1;
        } else if (opts.show_version) {
                printf("FUSE library version %s\n", fuse_pkgversion());
                fuse_lowlevel_version();
                ret = 0;
                goto err_out1;
        }
 
        /* Initial contents */
        update_fs();
 
        se = fuse_session_new(&args, &tfs_oper, sizeof(tfs_oper), NULL);
        if (se == NULL)
                goto err_out1;
 
        if (fuse_set_signal_handlers(se) != 0)
                goto err_out2;
 
        if (fuse_session_mount(se, opts.mountpoint) != 0)
                goto err_out3;
 
        fuse_daemonize(opts.foreground);
 
        /* Start thread to update file contents */
        ret = pthread_create(&updater, NULL, update_fs_loop, (void *)se);
        if (ret != 0) {
                fprintf(stderr, "pthread_create failed with %s\n",
                        strerror(ret));
                goto err_out3;
        }
 
        /* Block until ctrl+c or fusermount -u */
        if (opts.singlethread)
                ret = fuse_session_loop(se);
        else {
                config = fuse_loop_cfg_create();
                fuse_loop_cfg_set_clone_fd(config, opts.clone_fd);
                fuse_loop_cfg_set_max_threads(config, opts.max_threads);
                ret = fuse_session_loop_mt(se, config);
                fuse_loop_cfg_destroy(config);
                config = NULL;
        }
 
        assert(retrieve_status != 1);
        fuse_session_unmount(se);
err_out3:
        fuse_remove_signal_handlers(se);
err_out2:
        fuse_session_destroy(se);
err_out1:
        free(opts.mountpoint);
        fuse_opt_free_args(&args);
 
        return ret ? 1 : 0;
}