This example illustrates how to write a FUSE file system that supports polling for changes that don't come through the kernel. It can be tested with the poll_client.c program.
#define FUSE_USE_VERSION 31
#include <config.h>
#include <fuse.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>
#include <pthread.h>
#include <poll.h>
static unsigned fsel_open_mask;
static const char fsel_hex_map[] = "0123456789ABCDEF";
static struct fuse *fsel_fuse;
#define FSEL_CNT_MAX 10
#define FSEL_FILES 16
static pthread_mutex_t fsel_mutex;
static unsigned fsel_poll_notify_mask;
static struct fuse_pollhandle *fsel_poll_handle[FSEL_FILES];
static unsigned fsel_cnt[FSEL_FILES];
static int fsel_path_index(const char *path)
{
char ch = path[1];
if (strlen(path) != 2 || path[0] != '/' || !isxdigit(ch) || islower(ch))
return -1;
return ch <= '9' ? ch - '0' : ch - 'A' + 10;
}
static int fsel_getattr(const char *path, struct stat *stbuf,
{
(void) fi;
int idx;
memset(stbuf, 0, sizeof(struct stat));
if (strcmp(path, "/") == 0) {
stbuf->st_mode = S_IFDIR | 0555;
stbuf->st_nlink = 2;
return 0;
}
idx = fsel_path_index(path);
if (idx < 0)
return -ENOENT;
stbuf->st_mode = S_IFREG | 0444;
stbuf->st_nlink = 1;
stbuf->st_size = fsel_cnt[idx];
return 0;
}
static int fsel_readdir(
const char *path,
void *buf,
fuse_fill_dir_t filler,
{
char name[2] = { };
int i;
(void) offset;
(void) fi;
(void) flags;
if (strcmp(path, "/") != 0)
return -ENOENT;
for (i = 0; i < FSEL_FILES; i++) {
name[0] = fsel_hex_map[i];
filler(buf, name, NULL, 0, 0);
}
return 0;
}
{
int idx = fsel_path_index(path);
if (idx < 0)
return -ENOENT;
if ((fi->
flags & 3) != O_RDONLY)
return -EACCES;
if (fsel_open_mask & (1 << idx))
return -EBUSY;
fsel_open_mask |= (1 << idx);
return 0;
}
{
(void) path;
fsel_open_mask &= ~(1 << idx);
return 0;
}
static int fsel_read(const char *path, char *buf, size_t size, off_t offset,
{
(void) path;
(void) offset;
pthread_mutex_lock(&fsel_mutex);
if (fsel_cnt[idx] < size)
size = fsel_cnt[idx];
printf("READ %X transferred=%zu cnt=%u\n", idx, size, fsel_cnt[idx]);
fsel_cnt[idx] -= size;
pthread_mutex_unlock(&fsel_mutex);
memset(buf, fsel_hex_map[idx], size);
return size;
}
struct fuse_pollhandle *ph, unsigned *reventsp)
{
static unsigned polled_zero;
(void) path;
if (!fsel_fuse) {
if (cxt)
}
pthread_mutex_lock(&fsel_mutex);
if (ph != NULL) {
struct fuse_pollhandle *oldph = fsel_poll_handle[idx];
if (oldph)
fsel_poll_notify_mask |= (1 << idx);
fsel_poll_handle[idx] = ph;
}
if (fsel_cnt[idx]) {
*reventsp |= POLLIN;
printf("POLL %X cnt=%u polled_zero=%u\n",
idx, fsel_cnt[idx], polled_zero);
polled_zero = 0;
} else
polled_zero++;
pthread_mutex_unlock(&fsel_mutex);
return 0;
}
.readdir = fsel_readdir,
.open = fsel_open,
.release = fsel_release,
.read = fsel_read,
.poll = fsel_poll,
};
static void *fsel_producer(void *data)
{
const struct timespec interval = { 0, 250000000 };
unsigned idx = 0, nr = 1;
(void) data;
while (1) {
int i, t;
pthread_mutex_lock(&fsel_mutex);
for (i = 0, t = idx; i < nr;
i++, t = (t + FSEL_FILES / nr) % FSEL_FILES) {
if (fsel_cnt[t] == FSEL_CNT_MAX)
continue;
fsel_cnt[t]++;
if (fsel_fuse && (fsel_poll_notify_mask & (1 << t))) {
struct fuse_pollhandle *ph;
printf("NOTIFY %X\n", t);
ph = fsel_poll_handle[t];
fuse_notify_poll(ph);
fsel_poll_notify_mask &= ~(1 << t);
fsel_poll_handle[t] = NULL;
}
}
idx = (idx + 1) % FSEL_FILES;
if (idx == 0)
nr = (nr * 2) % 7;
pthread_mutex_unlock(&fsel_mutex);
nanosleep(&interval, NULL);
}
return NULL;
}
int main(int argc, char *argv[])
{
pthread_t producer;
pthread_attr_t attr;
int ret;
errno = pthread_mutex_init(&fsel_mutex, NULL);
if (errno) {
perror("pthread_mutex_init");
return 1;
}
errno = pthread_attr_init(&attr);
if (errno) {
perror("pthread_attr_init");
return 1;
}
errno = pthread_create(&producer, &attr, fsel_producer, NULL);
if (errno) {
perror("pthread_create");
return 1;
}
ret =
fuse_main(argc, argv, &fsel_oper, NULL);
pthread_cancel(producer);
pthread_join(producer, NULL);
return ret;
}