fuse_loop_mt.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>

  Implementation of the multi-threaded FUSE session loop.

  This program can be distributed under the terms of the GNU LGPLv2.
  See the file COPYING.LIB.
*/

#include "config.h"
#include "fuse_lowlevel.h"
#include "fuse_misc.h"
#include "fuse_kernel.h"
#include "fuse_i.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <semaphore.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <assert.h>

/* Environment var controlling the thread stack size */
#define ENVNAME_THREAD_STACK "FUSE_THREAD_STACK"

struct fuse_worker {
        struct fuse_worker *prev;
        struct fuse_worker *next;
        pthread_t thread_id;
        size_t bufsize;

        // We need to include fuse_buf so that we can properly free
        // it when a thread is terminated by pthread_cancel().
        struct fuse_buf fbuf;
        struct fuse_chan *ch;
        struct fuse_mt *mt;
};

struct fuse_mt {
        pthread_mutex_t lock;
        int numworker;
        int numavail;
        struct fuse_session *se;
        struct fuse_worker main;
        sem_t finish;
        int exit;
        int error;
        int clone_fd;
        int max_idle;
};

static struct fuse_chan *fuse_chan_new(int fd)
{
        struct fuse_chan *ch = (struct fuse_chan *) malloc(sizeof(*ch));
        if (ch == NULL) {
                fuse_log(FUSE_LOG_ERR, "fuse: failed to allocate channel\n");
                return NULL;
        }

        memset(ch, 0, sizeof(*ch));
        ch->fd = fd;
        ch->ctr = 1;
        fuse_mutex_init(&ch->lock);

        return ch;
}

struct fuse_chan *fuse_chan_get(struct fuse_chan *ch)
{
        assert(ch->ctr > 0);
        pthread_mutex_lock(&ch->lock);
        ch->ctr++;
        pthread_mutex_unlock(&ch->lock);

        return ch;
}

void fuse_chan_put(struct fuse_chan *ch)
{
        if (ch == NULL)
                return;
        pthread_mutex_lock(&ch->lock);
        ch->ctr--;
        if (!ch->ctr) {
                pthread_mutex_unlock(&ch->lock);
                close(ch->fd);
                pthread_mutex_destroy(&ch->lock);
                free(ch);
        } else
                pthread_mutex_unlock(&ch->lock);
}

static void list_add_worker(struct fuse_worker *w, struct fuse_worker *next)
{
        struct fuse_worker *prev = next->prev;
        w->next = next;
        w->prev = prev;
        prev->next = w;
        next->prev = w;
}

static void list_del_worker(struct fuse_worker *w)
{
        struct fuse_worker *prev = w->prev;
        struct fuse_worker *next = w->next;
        prev->next = next;
        next->prev = prev;
}

static int fuse_loop_start_thread(struct fuse_mt *mt);

static void *fuse_do_work(void *data)
{
        struct fuse_worker *w = (struct fuse_worker *) data;
        struct fuse_mt *mt = w->mt;

        while (!fuse_session_exited(mt->se)) {
                int isforget = 0;
                int res;

                pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
                res = fuse_session_receive_buf_int(mt->se, &w->fbuf, w->ch);
                pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
                if (res == -EINTR)
                        continue;
                if (res <= 0) {
                        if (res < 0) {
                                fuse_session_exit(mt->se);
                                mt->error = res;
                        }
                        break;
                }

                pthread_mutex_lock(&mt->lock);
                if (mt->exit) {
                        pthread_mutex_unlock(&mt->lock);
                        return NULL;
                }

                /*
                 * This disgusting hack is needed so that zillions of threads
                 * are not created on a burst of FORGET messages
                 */
                if (!(w->fbuf.flags & FUSE_BUF_IS_FD)) {
                        struct fuse_in_header *in = w->fbuf.mem;

                        if (in->opcode == FUSE_FORGET ||
                            in->opcode == FUSE_BATCH_FORGET)
                                isforget = 1;
                }

                if (!isforget)
                        mt->numavail--;
                if (mt->numavail == 0)
                        fuse_loop_start_thread(mt);
                pthread_mutex_unlock(&mt->lock);

                fuse_session_process_buf_int(mt->se, &w->fbuf, w->ch);

                pthread_mutex_lock(&mt->lock);
                if (!isforget)
                        mt->numavail++;
                if (mt->numavail > mt->max_idle) {
                        if (mt->exit) {
                                pthread_mutex_unlock(&mt->lock);
                                return NULL;
                        }
                        list_del_worker(w);
                        mt->numavail--;
                        mt->numworker--;
                        pthread_mutex_unlock(&mt->lock);

                        pthread_detach(w->thread_id);
                        free(w->fbuf.mem);
                        fuse_chan_put(w->ch);
                        free(w);
                        return NULL;
                }
                pthread_mutex_unlock(&mt->lock);
        }

        sem_post(&mt->finish);

        return NULL;
}

int fuse_start_thread(pthread_t *thread_id, void *(*func)(void *), void *arg)
{
        sigset_t oldset;
        sigset_t newset;
        int res;
        pthread_attr_t attr;
        char *stack_size;

        /* Override default stack size */
        pthread_attr_init(&attr);
        stack_size = getenv(ENVNAME_THREAD_STACK);
        if (stack_size && pthread_attr_setstacksize(&attr, atoi(stack_size)))
                fuse_log(FUSE_LOG_ERR, "fuse: invalid stack size: %s\n", stack_size);

        /* Disallow signal reception in worker threads */
        sigemptyset(&newset);
        sigaddset(&newset, SIGTERM);
        sigaddset(&newset, SIGINT);
        sigaddset(&newset, SIGHUP);
        sigaddset(&newset, SIGQUIT);
        pthread_sigmask(SIG_BLOCK, &newset, &oldset);
        res = pthread_create(thread_id, &attr, func, arg);
        pthread_sigmask(SIG_SETMASK, &oldset, NULL);
        pthread_attr_destroy(&attr);
        if (res != 0) {
                fuse_log(FUSE_LOG_ERR, "fuse: error creating thread: %s\n",
                        strerror(res));
                return -1;
        }

        return 0;
}

static struct fuse_chan *fuse_clone_chan(struct fuse_mt *mt)
{
        int res;
        int clonefd;
        uint32_t masterfd;
        struct fuse_chan *newch;
        const char *devname = "/dev/fuse";

#ifndef O_CLOEXEC
#define O_CLOEXEC 0
#endif
        clonefd = open(devname, O_RDWR | O_CLOEXEC);
        if (clonefd == -1) {
                fuse_log(FUSE_LOG_ERR, "fuse: failed to open %s: %s\n", devname,
                        strerror(errno));
                return NULL;
        }
        fcntl(clonefd, F_SETFD, FD_CLOEXEC);

        masterfd = mt->se->fd;
        res = ioctl(clonefd, FUSE_DEV_IOC_CLONE, &masterfd);
        if (res == -1) {
                fuse_log(FUSE_LOG_ERR, "fuse: failed to clone device fd: %s\n",
                        strerror(errno));
                close(clonefd);
                return NULL;
        }
        newch = fuse_chan_new(clonefd);
        if (newch == NULL)
                close(clonefd);

        return newch;
}

static int fuse_loop_start_thread(struct fuse_mt *mt)
{
        int res;

        struct fuse_worker *w = malloc(sizeof(struct fuse_worker));
        if (!w) {
                fuse_log(FUSE_LOG_ERR, "fuse: failed to allocate worker structure\n");
                return -1;
        }
        memset(w, 0, sizeof(struct fuse_worker));
        w->fbuf.mem = NULL;
        w->mt = mt;

        w->ch = NULL;
        if (mt->clone_fd) {
                w->ch = fuse_clone_chan(mt);
                if(!w->ch) {
                        /* Don't attempt this again */
                        fuse_log(FUSE_LOG_ERR, "fuse: trying to continue "
                                "without -o clone_fd.\n");
                        mt->clone_fd = 0;
                }
        }

        res = fuse_start_thread(&w->thread_id, fuse_do_work, w);
        if (res == -1) {
                fuse_chan_put(w->ch);
                free(w);
                return -1;
        }
        list_add_worker(w, &mt->main);
        mt->numavail ++;
        mt->numworker ++;

        return 0;
}

static void fuse_join_worker(struct fuse_mt *mt, struct fuse_worker *w)
{
        pthread_join(w->thread_id, NULL);
        pthread_mutex_lock(&mt->lock);
        list_del_worker(w);
        pthread_mutex_unlock(&mt->lock);
        free(w->fbuf.mem);
        fuse_chan_put(w->ch);
        free(w);
}

FUSE_SYMVER(".symver fuse_session_loop_mt_32,fuse_session_loop_mt@@FUSE_3.2");
int fuse_session_loop_mt_32(struct fuse_session *se, struct fuse_loop_config *config)
{
        int err;
        struct fuse_mt mt;
        struct fuse_worker *w;

        memset(&mt, 0, sizeof(struct fuse_mt));
        mt.se = se;
        mt.clone_fd = config->clone_fd;
        mt.error = 0;
        mt.numworker = 0;
        mt.numavail = 0;
        mt.max_idle = config->max_idle_threads;
        mt.main.thread_id = pthread_self();
        mt.main.prev = mt.main.next = &mt.main;
        sem_init(&mt.finish, 0, 0);
        fuse_mutex_init(&mt.lock);

        pthread_mutex_lock(&mt.lock);
        err = fuse_loop_start_thread(&mt);
        pthread_mutex_unlock(&mt.lock);
        if (!err) {
                /* sem_wait() is interruptible */
                while (!fuse_session_exited(se))
                        sem_wait(&mt.finish);

                pthread_mutex_lock(&mt.lock);
                for (w = mt.main.next; w != &mt.main; w = w->next)
                        pthread_cancel(w->thread_id);
                mt.exit = 1;
                pthread_mutex_unlock(&mt.lock);

                while (mt.main.next != &mt.main)
                        fuse_join_worker(&mt, mt.main.next);

                err = mt.error;
        }

        pthread_mutex_destroy(&mt.lock);
        sem_destroy(&mt.finish);
        if(se->error != 0)
                err = se->error;
        fuse_session_reset(se);
        return err;
}

int fuse_session_loop_mt_31(struct fuse_session *se, int clone_fd);
FUSE_SYMVER(".symver fuse_session_loop_mt_31,fuse_session_loop_mt@FUSE_3.0");
int fuse_session_loop_mt_31(struct fuse_session *se, int clone_fd)
{
        struct fuse_loop_config config;
        config.clone_fd = clone_fd;
        config.max_idle_threads = 10;
        return fuse_session_loop_mt_32(se, &config);
}