libfuse

notify_store_retrieve.c File Reference
`#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>`

Go to the source code of this file.

## Detailed Description

This example implements a file system with a single file whose contents change dynamically: it always contains the current time.

While notify_inval_inode.c uses fuse_lowlevel_notify_inval_inode() to let the kernel know that it has to invalidate the cache, this example actively pushes the updated data into the kernel cache using fuse_lowlevel_notify_store().

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

    $ notify_store_retrieve --update-interval=1 --no-notify mnt/

Observe that the output never changes, even though the file system updates it once per second. This is because the contents are cached in the kernel:

    $ for i in 1 2 3 4 5; do
    >     cat mnt/current_time
    >     sleep 1
    > done
    The current time is 15:58:18
    The current time is 15:58:18
    The current time is 15:58:18
    The current time is 15:58:18
    The current time is 15:58:18

If you instead enable the notification functions, the changes become visible:

    $ notify_store_retrieve --update-interval=1 mnt/
    $ for i in 1 2 3 4 5; do
    >     cat mnt/current_time
    >     sleep 1
    > done
    The current time is 15:58:40
    The current time is 15:58:41
    The current time is 15:58:42
    The current time is 15:58:43
    The current time is 15:58:44

## Compilation

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

## 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 GPLv2.
See the file COPYING.
*/
#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 *now;
time_t t;
t = time(NULL);
now = localtime(&t);
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;
}
fuse_set_signal_handlers
int fuse_set_signal_handlers(struct fuse_session *se)
Definition fuse_signals.c:138
fuse_buf_copy
ssize_t fuse_buf_copy(struct fuse_bufvec *dst, struct fuse_bufvec *src, enum fuse_buf_copy_flags flags)
Definition buffer.c:284
fuse_pkgversion
const char * fuse_pkgversion(void)
Definition fuse.c:5218
fuse_remove_signal_handlers
void fuse_remove_signal_handlers(struct fuse_session *se)
Definition fuse_signals.c:180
fuse_daemonize
int fuse_daemonize(int foreground)
Definition helper.c:253
fuse_session_destroy
void fuse_session_destroy(struct fuse_session *se)
Definition fuse_lowlevel.c:2967
fuse_reply_open
int fuse_reply_open(fuse_req_t req, const struct fuse_file_info *fi)
Definition fuse_lowlevel.c:508
fuse_reply_err
int fuse_reply_err(fuse_req_t req, int err)
Definition fuse_lowlevel.c:334
fuse_reply_buf
int fuse_reply_buf(fuse_req_t req, const char *buf, size_t size)
Definition fuse_lowlevel.c:527
fuse_req_t
struct fuse_req * fuse_req_t
Definition fuse_lowlevel.h:50
fuse_lowlevel_notify_retrieve
int fuse_lowlevel_notify_retrieve(struct fuse_session *se, fuse_ino_t ino, size_t size, off_t offset, void *cookie)
Definition fuse_lowlevel.c:2625
fuse_session_loop
int fuse_session_loop(struct fuse_session *se)
Definition fuse_loop.c:19
fuse_reply_entry
int fuse_reply_entry(fuse_req_t req, const struct fuse_entry_param *e)
Definition fuse_lowlevel.c:431
fuse_session_unmount
void fuse_session_unmount(struct fuse_session *se)
Definition fuse_lowlevel.c:3479
fuse_cmdline_help
void fuse_cmdline_help(void)
Definition helper.c:130
fuse_reply_none
void fuse_reply_none(fuse_req_t req)
Definition fuse_lowlevel.c:339
fuse_lowlevel_help
void fuse_lowlevel_help(void)
Definition fuse_lowlevel.c:2957
fuse_session_mount
int fuse_session_mount(struct fuse_session *se, const char *mountpoint)
Definition fuse_lowlevel.c:3419
fuse_lowlevel_version
void fuse_lowlevel_version(void)
Definition fuse_lowlevel.c:2950
fuse_ino_t
uint64_t fuse_ino_t
Definition fuse_lowlevel.h:47
fuse_add_direntry
size_t fuse_add_direntry(fuse_req_t req, char *buf, size_t bufsize, const char *name, const struct stat *stbuf, off_t off)
Definition fuse_lowlevel.c:289
fuse_reply_attr
int fuse_reply_attr(fuse_req_t req, const struct stat *attr, double attr_timeout)
Definition fuse_lowlevel.c:463
fuse_lowlevel_notify_store
int fuse_lowlevel_notify_store(struct fuse_session *se, fuse_ino_t ino, off_t offset, struct fuse_bufvec *bufv, enum fuse_buf_copy_flags flags)
Definition fuse_lowlevel.c:2545
fuse_opt_free_args
void fuse_opt_free_args(struct fuse_args *args)
Definition fuse_opt.c:34
fuse_opt_parse
int fuse_opt_parse(struct fuse_args *args, void *data, const struct fuse_opt opts[], fuse_opt_proc_t proc)
Definition fuse_opt.c:398
FUSE_ARGS_INIT
#define FUSE_ARGS_INIT(argc, argv)
Definition fuse_opt.h:123
FUSE_OPT_END
#define FUSE_OPT_END
Definition fuse_opt.h:104
FUSE_ROOT_ID
#define FUSE_ROOT_ID
Definition fuse_lowlevel.h:44
fuse_args
Definition fuse_opt.h:109
fuse_args::argc
int argc
Definition fuse_opt.h:111
fuse_args::argv
char ** argv
Definition fuse_opt.h:114
fuse_buf::flags
enum fuse_buf_flags flags
Definition fuse_common.h:902
fuse_bufvec
Definition fuse_common.h:942
fuse_bufvec::buf
struct fuse_buf buf[1]
Definition fuse_common.h:961
fuse_cmdline_opts
Definition fuse_lowlevel.h:2001
fuse_conn_info
Definition fuse_common.h:555
fuse_conn_info::no_interrupt
uint32_t no_interrupt
Definition fuse_common.h:694
fuse_entry_param
Definition fuse_lowlevel.h:60
fuse_entry_param::ino
fuse_ino_t ino
Definition fuse_lowlevel.h:68
fuse_file_info
Definition fuse_common.h:58
fuse_file_info::keep_cache
uint32_t keep_cache
Definition fuse_common.h:77
fuse_file_info::flags
int32_t flags
Definition fuse_common.h:60
fuse_loop_config
Definition fuse_common.h:149
fuse_lowlevel_ops
Definition fuse_lowlevel.h:206
fuse_lowlevel_ops::init
void(* init)(void *userdata, struct fuse_conn_info *conn)
Definition fuse_lowlevel.h:223
fuse_opt
Definition fuse_opt.h:77

Definition in file notify_store_retrieve.c.