notify_inval_entry.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 <signal.h>
#include <stddef.h>
#include <sys/stat.h>
#include <unistd.h>
#include <pthread.h>
 
#define MAX_STR_LEN 128
static char file_name[MAX_STR_LEN];
static fuse_ino_t file_ino = 2;
static int lookup_cnt = 0;
static pthread_t main_thread;
 
/* Command line parsing */
struct options {
        int no_notify;
        float timeout;
        int update_interval;
        int only_expire;
        int inc_epoch;
};
static struct options options = {
        .timeout = 5,
        .no_notify = 0,
        .update_interval = 1,
        .only_expire = 0,
        .inc_epoch = 0,
};
 
#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),
        OPTION("--timeout=%f", timeout),
        OPTION("--only-expire", only_expire),
        OPTION("--inc-epoch", inc_epoch),
        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 | 0000;
                stbuf->st_nlink = 1;
                stbuf->st_size = 0;
        }
 
        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;
                lookup_cnt++;
        } else
                goto err_out;
 
        e.attr_timeout = options.timeout;
        e.entry_timeout = options.timeout;
        if (tfs_stat(e.ino, &e.attr) != 0)
                goto err_out;
        fuse_reply_entry(req, &e);
        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)
                lookup_cnt -= nlookup;
        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, options.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 const struct fuse_lowlevel_ops tfs_oper = {
        .init = tfs_init,
        .lookup = tfs_lookup,
        .getattr = tfs_getattr,
        .readdir = tfs_readdir,
        .forget = tfs_forget,
};
 
static void update_fs(void)
{
        time_t t;
        struct tm tmbuf;
        struct tm *now;
        ssize_t ret;
 
        t = time(NULL);
        now = localtime_r(&t, &tmbuf);
        assert(now != NULL);
 
        ret = strftime(file_name, MAX_STR_LEN, "Time_is_%Hh_%Mm_%Ss", now);
        assert(ret != 0);
}
 
static void *update_fs_loop(void *data)
{
        struct fuse_session *se = (struct fuse_session *)data;
        char *old_name;
        int ret = 0;
 
        while (!fuse_session_exited(se)) {
                old_name = strdup(file_name);
                update_fs();
 
                if (!options.no_notify && lookup_cnt) {
                        if (options.only_expire) { // expire entry
                                ret = fuse_lowlevel_notify_expire_entry(
                                        se, FUSE_ROOT_ID, old_name,
                                        strlen(old_name));
 
                                // no kernel support
                                if (ret == -ENOSYS) {
                                        printf("%s not supported by kernel\n",
                                               "fuse_lowlevel_notify_expire_entry");
                                        break;
                                }
 
                                // 1) ret == 0: successful expire of an existing entry
                                // 2) ret == -ENOENT: kernel has already expired the entry /
                                //                    entry does not exist anymore in the kernel
                                assert(ret == 0 || ret == -ENOENT);
                        } else if (options.inc_epoch) { // increment epoch
                                ret = fuse_lowlevel_notify_increment_epoch(se);
 
                                if (ret == -ENOSYS) {
                                        printf("%s not supported by kernel\n",
                                               "fuse_lowlevel_notify_increment_epoch");
                                        break;
                                }
                                assert(ret == 0);
                        } else { // invalidate entry
                                assert(fuse_lowlevel_notify_inval_entry(
                                               se, FUSE_ROOT_ID, old_name,
                                               strlen(old_name)) == 0);
                        }
                }
                free(old_name);
                sleep(options.update_interval);
        }
 
        if (ret == -ENOSYS) {
                printf("Exiting...\n");
 
                fuse_session_exit(se);
                // Make sure to exit now, rather than on next request from userspace
                pthread_kill(main_thread, SIGPIPE);
        }
 
        return NULL;
}
 
static void show_help(const char *progname)
{
        printf("usage: %s [options] <mountpoint>\n\n", progname);
        printf("File-system specific options:\n"
               "    --timeout=<secs>       Timeout for kernel caches\n"
               "    --update-interval=<secs>  Update-rate of file system contents\n"
               "    --no-notify            Disable kernel notifications\n"
               "    --only-expire          Expire entries instead of invalidating them\n"
               "    --inc-epoch            Increment epoch, invalidating all dentries\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;
        pthread_t updater;
        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;
        }
        if (options.only_expire && options.inc_epoch) {
                printf("'only-expire' and 'inc-epoch' options are exclusive\n");
                ret = 0;
                goto err_out1;
        }
 
        /* Initial contents */
        update_fs();
 
        se = fuse_session_new(&args, &tfs_oper, sizeof(tfs_oper), &se);
        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);
 
        // Needed to ensure that the main thread continues/restarts processing as soon
        // as the fuse session ends (immediately after calling fuse_session_exit() )
        // and not only on the next request from userspace
        main_thread = pthread_self();
 
        /* 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;
        }
 
        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;
}