fusehalt.c

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

  This code was adapted from fuse example code to provide
  switchable blocking on IO operations.

  Halting updates by Jon Hoffman <jonhoffman@gmail.com>
  
  This program can be distributed under the terms of the GNU GPL.

  gcc -Wall `pkg-config fuse --cflags --libs` fusehalt.c -o fusehalt
*/

#define FUSE_USE_VERSION 26


#ifdef linux
/* For pread()/pwrite() */
#define _XOPEN_SOURCE 500
#endif

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <sys/time.h>
#ifdef HAVE_SETXATTR
#include <sys/xattr.h>
#endif
#include <time.h>
#include <pthread.h>
#include <malloc.h>

char * halt_file;
unsigned char halted = 0;
unsigned char not_destroyed = 1;

static void do_halt(void) 
{
    while ( halted == 1 ) {
        sleep(1);
    }
}

static int xmp_getattr(const char *path, struct stat *stbuf)
{
    int res;
    do_halt();
    res = lstat(path, stbuf);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_access(const char *path, int mask)
{
    int res;
    do_halt();
    res = access(path, mask);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_readlink(const char *path, char *buf, size_t size)
{
    int res;
    do_halt();
    res = readlink(path, buf, size - 1);
    if (res == -1)
        return -errno;

    buf[res] = '\0';
    return 0;
}


static int xmp_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
               off_t offset, struct fuse_file_info *fi)
{
    DIR *dp;
    struct dirent *de;

    (void) offset;
    (void) fi;

    dp = opendir(path);
    if (dp == NULL)
        return -errno;

    while ((de = readdir(dp)) != NULL) {
        struct stat st;
        memset(&st, 0, sizeof(st));
        st.st_ino = de->d_ino;
        st.st_mode = de->d_type << 12;
        if (filler(buf, de->d_name, &st, 0))
            break;
    }

    closedir(dp);
    return 0;
}

static int xmp_mknod(const char *path, mode_t mode, dev_t rdev)
{
    int res;
    do_halt();
    /* On Linux this could just be 'mknod(path, mode, rdev)' but this
       is more portable */
    if (S_ISREG(mode)) {
        res = open(path, O_CREAT | O_EXCL | O_WRONLY, mode);
        if (res >= 0)
            res = close(res);
    } else if (S_ISFIFO(mode))
        res = mkfifo(path, mode);
    else
        res = mknod(path, mode, rdev);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_mkdir(const char *path, mode_t mode)
{
    int res;

    res = mkdir(path, mode);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_unlink(const char *path)
{
    int res;

    res = unlink(path);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_rmdir(const char *path)
{
    int res;

    res = rmdir(path);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_symlink(const char *from, const char *to)
{
    int res;

    res = symlink(from, to);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_rename(const char *from, const char *to)
{
    int res;

    res = rename(from, to);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_link(const char *from, const char *to)
{
    int res;

    res = link(from, to);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_chmod(const char *path, mode_t mode)
{
    int res;

    res = chmod(path, mode);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_chown(const char *path, uid_t uid, gid_t gid)
{
    int res;

    res = lchown(path, uid, gid);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_truncate(const char *path, off_t size)
{
    int res;

    res = truncate(path, size);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_utimens(const char *path, const struct timespec ts[2])
{
    int res;
    struct timeval tv[2];

    tv[0].tv_sec = ts[0].tv_sec;
    tv[0].tv_usec = ts[0].tv_nsec / 1000;
    tv[1].tv_sec = ts[1].tv_sec;
    tv[1].tv_usec = ts[1].tv_nsec / 1000;

    res = utimes(path, tv);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_open(const char *path, struct fuse_file_info *fi)
{
    int res;
    do_halt();
    res = open(path, fi->flags);
    if (res == -1)
        return -errno;

    close(res);
    return 0;
}



static int xmp_read(const char *path, char *buf, size_t size, off_t offset,
            struct fuse_file_info *fi)
{
    int fd;
    int res;

    (void) fi;
    do_halt();
    fd = open(path, O_RDONLY);
    if (fd == -1)
        return -errno;

    res = pread(fd, buf, size, offset);
    if (res == -1)
        res = -errno;

    close(fd);
    return res;
}

static int xmp_write(const char *path, const char *buf, size_t size,
             off_t offset, struct fuse_file_info *fi)
{
    int fd;
    int res;

    (void) fi;
    do_halt();
    fd = open(path, O_WRONLY);
    if (fd == -1)
        return -errno;

    res = pwrite(fd, buf, size, offset);
    if (res == -1)
        res = -errno;

    close(fd);
    return res;
}

static int xmp_statfs(const char *path, struct statvfs *stbuf)
{
    int res;
    do_halt();
    res = statvfs(path, stbuf);
    if (res == -1)
        return -errno;

    return 0;
}

static int xmp_release(const char *path, struct fuse_file_info *fi)
{
    /* Just a stub.  This method is optional and can safely be left
       unimplemented */

    (void) path;
    (void) fi;
    return 0;
}

static int xmp_fsync(const char *path, int isdatasync,
             struct fuse_file_info *fi)
{
    /* Just a stub.  This method is optional and can safely be left
       unimplemented */
    do_halt();
    (void) path;
    (void) isdatasync;
    (void) fi;
    return 0;
}

#ifdef HAVE_SETXATTR
/* xattr operations are optional and can safely be left unimplemented */
static int xmp_setxattr(const char *path, const char *name, const char *value,
            size_t size, int flags)
{
    int res = lsetxattr(path, name, value, size, flags);
    if (res == -1)
        return -errno;
    return 0;
}

static int xmp_getxattr(const char *path, const char *name, char *value,
            size_t size)
{
    int res = lgetxattr(path, name, value, size);
    if (res == -1)
        return -errno;
    return res;
}

static int xmp_listxattr(const char *path, char *list, size_t size)
{
    int res = llistxattr(path, list, size);
    if (res == -1)
        return -errno;
    return res;
}

static int xmp_removexattr(const char *path, const char *name)
{
    int res = lremovexattr(path, name);
    if (res == -1)
        return -errno;
    return 0;
}
#endif /* HAVE_SETXATTR */

void *threadFunc(void *arg)
{
    printf("fusehalt: child thread watching %s\n", halt_file);
    while( not_destroyed ) 
    {
        FILE *fp = fopen(halt_file, "r");
        if (!fp) 
        {
          if (halted == 1) 
          {
            puts("fusehalt: unhalting fs operations"); 
            halted = 0;
          }
        } else {
          if (halted == 0) 
          {
            puts("fusehalt: halting fs operations");
            halted = 1;
          }
          fclose( fp );
        }
        sleep(1);
    }
    puts("fusehalt: child thread exiting");
    pthread_exit(NULL);
    return 0;
}

static void * xmp_init(struct fuse_conn_info *conn)
{
    pthread_t myThread;
    pthread_create(&myThread, NULL, threadFunc, NULL);
    return 0;
}

static void xmp_destroy(void *context)
{
    not_destroyed = 0;
}

static struct fuse_operations xmp_oper = {
    .getattr    = xmp_getattr,
    .access     = xmp_access,
    .readlink   = xmp_readlink,
    .readdir    = xmp_readdir,
    .mknod      = xmp_mknod,
    .mkdir      = xmp_mkdir,
    .symlink    = xmp_symlink,
    .unlink     = xmp_unlink,
    .rmdir      = xmp_rmdir,
    .rename     = xmp_rename,
    .link       = xmp_link,
    .chmod      = xmp_chmod,
    .chown      = xmp_chown,
    .truncate   = xmp_truncate,
    .utimens    = xmp_utimens,
    .open       = xmp_open,
    .read       = xmp_read,
    .write      = xmp_write,
    .statfs     = xmp_statfs,
    .release    = xmp_release,
    .fsync      = xmp_fsync,
    .init       = xmp_init,
    .destroy    = xmp_destroy,
#ifdef HAVE_SETXATTR
    .setxattr   = xmp_setxattr,
    .getxattr   = xmp_getxattr,
    .listxattr  = xmp_listxattr,
    .removexattr    = xmp_removexattr,
#endif
};

int main(int argc, char *argv[])
{
    int i;
    struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
     
    umask(0);
    for(i = 0; i < argc; i++) {
        if (i == 2)
            halt_file = argv[i];
        else
            fuse_opt_add_arg(&args, argv[i]);
    }
    return fuse_main(args.argc, args.argv, &xmp_oper, NULL);
}