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.