poll.c File Reference
`#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>`

Go to the source code of this file.

## Detailed Description

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.

Compile with:

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

## Source code

/*
FUSE fsel: FUSE select example
Copyright (C) 2008 SUSE Linux Products GmbH
Copyright (C) 2008 Tejun Heo <teheo@suse.de>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
*/
#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>
/*
* fsel_open_mask is used to limit the number of opens to 1 per file.
* This is to use file index (0-F) as fh as poll support requires
* unique fh per open file. Lifting this would require proper open
* file management.
*/
static unsigned fsel_open_mask;
static const char fsel_hex_map[] = "0123456789ABCDEF";
static struct fuse *fsel_fuse; /* needed for poll notification */
#define FSEL_CNT_MAX 10 /* each file can store upto 10 chars */
#define FSEL_FILES 16
static pthread_mutex_t fsel_mutex; /* protects notify_mask and cnt array */
static unsigned fsel_poll_notify_mask; /* poll notification scheduled? */
static struct fuse_pollhandle *fsel_poll_handle[FSEL_FILES]; /* poll notify handles */
static unsigned fsel_cnt[FSEL_FILES]; /* nbytes stored in each file */
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,
struct fuse_file_info *fi)
{
(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,
off_t offset, struct fuse_file_info *fi,
enum fuse_readdir_flags flags)
{
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;
}
static int fsel_open(const char *path, struct fuse_file_info *fi)
{
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);
/*
* fsel files are nonseekable somewhat pipe-like files which
* gets filled up periodically by producer thread and consumed
* on read. Tell FUSE as such.
*/
fi->fh = idx;
fi->direct_io = 1;
fi->nonseekable = 1;
return 0;
}
static int fsel_release(const char *path, struct fuse_file_info *fi)
{
int idx = fi->fh;
(void) path;
fsel_open_mask &= ~(1 << idx);
return 0;
}
static int fsel_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
int idx = fi->fh;
(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;
}
static int fsel_poll(const char *path, struct fuse_file_info *fi,
struct fuse_pollhandle *ph, unsigned *reventsp)
{
static unsigned polled_zero;
int idx = fi->fh;
(void) path;
/*
* Poll notification requires pointer to struct fuse which
* can't be obtained when using fuse_main(). As notification
* happens only after poll is called, fill it here from
* fuse_context.
*/
if (!fsel_fuse) {
struct fuse_context *cxt = fuse_get_context();
if (cxt)
fsel_fuse = cxt->fuse;
}
pthread_mutex_lock(&fsel_mutex);
if (ph != NULL) {
struct fuse_pollhandle *oldph = fsel_poll_handle[idx];
if (oldph)
fuse_pollhandle_destroy(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;
}
static struct fuse_operations fsel_oper = {
.getattr = fsel_getattr,
.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);
/*
* This is the main producer loop which is executed
* ever 500ms. On each iteration, it fills one byte
* to 1, 2 or 4 files and sends poll notification if
* requested.
*/
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);
fuse_pollhandle_destroy(ph);
fsel_poll_notify_mask &= ~(1 << t);
fsel_poll_handle[t] = NULL;
}
}
idx = (idx + 1) % FSEL_FILES;
if (idx == 0)
nr = (nr * 2) % 7; /* cycle through 1, 2 and 4 */
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;
}

Definition in file poll.c.