libfuse
notify_inval_entry.c File Reference
#include <config.h>
#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>

Detailed Description

This example implements a file system with a single file whose file name changes dynamically to reflect the current time.

It illustrates the use of the fuse_lowlevel_notify_inval_entry() function.

To see the effect, first start the file system with the --no-notify

$ notify_inval_entry --update-interval=1 --timeout 30 --no-notify mnt/

Observe that ls always prints the correct directory contents (since readdir output is not cached)::

$ ls mnt; sleep 1; ls mnt; sleep 1; ls mnt
Time_is_15h_48m_33s  current_time
Time_is_15h_48m_34s  current_time
Time_is_15h_48m_35s  current_time

However, if you try to access a file by name the kernel will report that it still exists:

$ file=$(ls mnt/); echo $file
Time_is_15h_50m_09s
$ sleep 5; stat mnt/$file
  File: ‘mnt/Time_is_15h_50m_09s’
  Size: 32                Blocks: 0          IO Block: 4096   regular file
Device: 2ah/42d     Inode: 3           Links: 1
Access: (0444/-r--r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 1969-12-31 16:00:00.000000000 -0800
Modify: 1969-12-31 16:00:00.000000000 -0800
Change: 1969-12-31 16:00:00.000000000 -0800
 Birth: -

Only once the kernel cache timeout has been reached will the stat call fail:

$ sleep 30; stat mnt/$file
stat: cannot stat ‘mnt/Time_is_15h_50m_09s’: No such file or directory

In contrast, if you enable notifications you will be unable to stat the file as soon as the file system updates its name:

$ notify_inval_entry --update-interval=1 --timeout 30 --no-notify mnt/
$ file=$(ls mnt/); stat mnt/$file
  File: ‘mnt/Time_is_20h_42m_11s’
  Size: 0                 Blocks: 0          IO Block: 4096   regular empty file
Device: 2ah/42d     Inode: 2           Links: 1
Access: (0000/----------)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 1969-12-31 16:00:00.000000000 -0800
Modify: 1969-12-31 16:00:00.000000000 -0800
Change: 1969-12-31 16:00:00.000000000 -0800
 Birth: -
$ sleep 1; stat mnt/$file
stat: cannot stat ‘mnt/Time_is_20h_42m_11s’: No such file or directory

Compilation

gcc -Wall notify_inval_entry.c `pkg-config fuse3 --cflags --libs` -o notify_inval_entry

Source code

/*
FUSE: Filesystem in Userspace
Copyright (C) 2016 Nikolaus Rath <Nikolaus@rath.org>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
*/
#define FUSE_USE_VERSION 30
#include <config.h>
#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>
#define MAX_STR_LEN 128
static char file_name[MAX_STR_LEN];
static fuse_ino_t file_ino = 2;
static int lookup_cnt = 0;
/* Command line parsing */
struct options {
int no_notify;
float timeout;
int update_interval;
};
static struct options options = {
.timeout = 5,
.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),
OPTION("--timeout=%f", timeout),
};
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_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);
}
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 struct fuse_lowlevel_ops tfs_oper = {
.lookup = tfs_lookup,
.getattr = tfs_getattr,
.readdir = tfs_readdir,
.forget = tfs_forget,
};
static void update_fs(void) {
time_t t;
struct tm *now;
ssize_t ret;
t = time(NULL);
now = localtime(&t);
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;
while(1) {
old_name = strdup(file_name);
update_fs();
if (!options.no_notify && lookup_cnt)
(se, FUSE_ROOT_ID, old_name, strlen(old_name)) == 0);
free(old_name);
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"
" --timeout=<secs> Timeout for kernel caches\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;
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]);
ret = 0;
goto err_out1;
} else if (opts.show_version) {
printf("FUSE library version %s\n", fuse_pkgversion());
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;
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
ret = fuse_session_loop_mt(se, opts.clone_fd);
err_out3:
err_out2:
err_out1:
free(opts.mountpoint);
return ret ? 1 : 0;
}