mergerfs/libfuse/lib/ulockmgr.c

/*
  libulockmgr: Userspace Lock Manager Library
  Copyright (C) 2006  Miklos Szeredi <miklos@szeredi.hu>

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

/* #define DEBUG 1 */

#include "ulockmgr.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>
#include <assert.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/wait.h>

struct message {
  unsigned intr : 1;
  unsigned nofd : 1;
  pthread_t thr;
  int cmd;
  int fd;
  struct flock lock;
  int error;
};

struct fd_store {
  struct fd_store *next;
  int fd;
  int inuse;
};

struct owner {
  struct owner *next;
  struct owner *prev;
  struct fd_store *fds;
  void *id;
  size_t id_len;
  int cfd;
};

static pthread_mutex_t ulockmgr_lock;
static int ulockmgr_cfd = -1;
static struct owner owner_list = { .next = &owner_list, .prev = &owner_list };

#define MAX_SEND_FDS 2

static void list_del_owner(struct owner *owner)
{
  struct owner *prev = owner->prev;
  struct owner *next = owner->next;
  prev->next = next;
  next->prev = prev;
}

static void list_add_owner(struct owner *owner, struct owner *next)
{
  struct owner *prev = next->prev;
  owner->next = next;
  owner->prev = prev;
  prev->next = owner;
  next->prev = owner;
}

/*
 * There's a bug in the linux kernel (< 2.6.22) recv() implementation
 * on AF_UNIX, SOCK_STREAM sockets, that could cause it to return
 * zero, even if data was available.  Retrying the recv will return
 * the data in this case.
 */
static int do_recv(int sock, void *buf, size_t len, int flags)
{
  int res = recv(sock, buf, len, flags);
  if (res == 0)
    res = recv(sock, buf, len, flags);

  return res;
}

static int ulockmgr_send_message(int sock, void *buf, size_t buflen,
				 int *fdp, int numfds)
{
  struct msghdr msg;
  struct cmsghdr *p_cmsg;
  struct iovec vec;
  size_t cmsgbuf[CMSG_SPACE(sizeof(int) * MAX_SEND_FDS) / sizeof(size_t)];
  int res;

  assert(numfds <= MAX_SEND_FDS);
  msg.msg_control = cmsgbuf;
  msg.msg_controllen = sizeof(cmsgbuf);
  p_cmsg = CMSG_FIRSTHDR(&msg);
  p_cmsg->cmsg_level = SOL_SOCKET;
  p_cmsg->cmsg_type = SCM_RIGHTS;
  p_cmsg->cmsg_len = CMSG_LEN(sizeof(int) * numfds);
  memcpy(CMSG_DATA(p_cmsg), fdp, sizeof(int) * numfds);
  msg.msg_controllen = p_cmsg->cmsg_len;
  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  msg.msg_iov = &vec;
  msg.msg_iovlen = 1;
  msg.msg_flags = 0;
  vec.iov_base = buf;
  vec.iov_len = buflen;
  res = sendmsg(sock, &msg, MSG_NOSIGNAL);
  if (res == -1) {
    perror("libulockmgr: sendmsg");
    return -1;
  }
  if ((size_t) res != buflen) {
    fprintf(stderr, "libulockmgr: sendmsg short\n");
    return -1;
  }
  return 0;
}

static int ulockmgr_start_daemon(void)
{
  int sv[2];
  int res;
  char tmp[64];

  res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
  if (res == -1) {
    perror("libulockmgr: socketpair");
    return -1;
  }
  snprintf(tmp, sizeof(tmp), "exec ulockmgr_server %i", sv[0]);
  res = system(tmp);
  close(sv[0]);
  if (res == -1 || !WIFEXITED(res) || WEXITSTATUS(res) != 0) {
    close(sv[1]);
    return -1;
  }
  ulockmgr_cfd = sv[1];
  return 0;
}

static struct owner *ulockmgr_new_owner(const void *id, size_t id_len)
{
  int sv[2];
  int res;
  char c = 'm';
  struct owner *o;

  if (ulockmgr_cfd == -1 && ulockmgr_start_daemon() == -1)
    return NULL;

  o = calloc(1, sizeof(struct owner) + id_len);
  if (!o) {
    fprintf(stderr, "libulockmgr: failed to allocate memory\n");
    return NULL;
  }
  o->id = o + 1;
  o->id_len = id_len;
  res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
  if (res == -1) {
    perror("libulockmgr: socketpair");
    goto out_free;
  }
  res = ulockmgr_send_message(ulockmgr_cfd, &c, sizeof(c), &sv[0], 1);
  close(sv[0]);
  if (res == -1) {
    close(ulockmgr_cfd);
    ulockmgr_cfd = -1;
    goto out_close;
  }

  o->cfd = sv[1];
  memcpy(o->id, id, id_len);
  list_add_owner(o, &owner_list);

  return o;

 out_close:
  close(sv[1]);
 out_free:
  free(o);
  return NULL;
}

static int ulockmgr_send_request(struct message *msg, const void *id,
				 size_t id_len)
{
  int sv[2];
  int cfd;
  struct owner *o;
  struct fd_store *f = NULL;
  struct fd_store *newf = NULL;
  struct fd_store **fp;
  int fd = msg->fd;
  int cmd = msg->cmd;
  int res;
  int unlockall = (cmd == F_SETLK && msg->lock.l_type == F_UNLCK &&
                   msg->lock.l_start == 0 && msg->lock.l_len == 0);

  for (o = owner_list.next; o != &owner_list; o = o->next)
    if (o->id_len == id_len && memcmp(o->id, id, id_len) == 0)
      break;

  if (o == &owner_list)
    o = NULL;

  if (!o && cmd != F_GETLK && msg->lock.l_type != F_UNLCK)
    o = ulockmgr_new_owner(id, id_len);

  if (!o) {
    if (cmd == F_GETLK) {
      res = fcntl(msg->fd, F_GETLK, &msg->lock);
      return (res == -1) ? -errno : 0;
    } else if (msg->lock.l_type == F_UNLCK)
      return 0;
    else
      return -ENOLCK;
  }

  if (unlockall)
    msg->nofd = 1;
  else {
    for (fp = &o->fds; *fp; fp = &(*fp)->next) {
      f = *fp;
      if (f->fd == fd) {
        msg->nofd = 1;
        break;
      }
    }
  }

  if (!msg->nofd) {
    newf = f = calloc(1, sizeof(struct fd_store));
    if (!f) {
      fprintf(stderr, "libulockmgr: failed to allocate memory\n");
      return -ENOLCK;
    }
  }

  res = socketpair(AF_UNIX, SOCK_STREAM, 0, sv);
  if (res == -1) {
    perror("libulockmgr: socketpair");
    free(newf);
    return -ENOLCK;
  }

  cfd = sv[1];
  sv[1] = msg->fd;
  res = ulockmgr_send_message(o->cfd, msg, sizeof(struct message), sv,
                              msg->nofd ? 1 : 2);
  close(sv[0]);
  if (res == -1) {
    free(newf);
    close(cfd);
    return -EIO;
  }

  if (newf) {
    newf->fd = msg->fd;
    newf->next = o->fds;
    o->fds = newf;
  }
  if (f)
    f->inuse++;

  res = do_recv(cfd, msg, sizeof(struct message), MSG_WAITALL);
  if (res == -1) {
    perror("libulockmgr: recv");
    msg->error = EIO;
  } else if (res != sizeof(struct message)) {
    fprintf(stderr, "libulockmgr: recv short\n");
    msg->error = EIO;
  } else if (cmd == F_SETLKW && msg->error == EAGAIN) {
    pthread_mutex_unlock(&ulockmgr_lock);
    while (1) {
      sigset_t old;
      sigset_t unblock;
      int errno_save;

      sigemptyset(&unblock);
      sigaddset(&unblock, SIGUSR1);
      pthread_sigmask(SIG_UNBLOCK, &unblock, &old);
      res = do_recv(cfd, msg, sizeof(struct message),
                    MSG_WAITALL);
      errno_save = errno;
      pthread_sigmask(SIG_SETMASK, &old, NULL);
      if (res == sizeof(struct message))
        break;
      else if (res >= 0) {
        fprintf(stderr, "libulockmgr: recv short\n");
        msg->error = EIO;
        break;
      } else if (errno_save != EINTR) {
        errno = errno_save;
        perror("libulockmgr: recv");
        msg->error = EIO;
        break;
      }
      msg->intr = 1;
      res = send(o->cfd, msg, sizeof(struct message),
                 MSG_NOSIGNAL);
      if (res == -1) {
        perror("libulockmgr: send");
        msg->error = EIO;
        break;
      }
      if (res != sizeof(struct message)) {
        fprintf(stderr, "libulockmgr: send short\n");
        msg->error = EIO;
        break;
      }
    }
    pthread_mutex_lock(&ulockmgr_lock);

  }
  if (f)
    f->inuse--;
  close(cfd);
  if (unlockall) {
    for (fp = &o->fds; *fp;) {
      f = *fp;
      if (f->fd == fd && !f->inuse) {
        *fp = f->next;
        free(f);
      } else
        fp = &f->next;
    }
    if (!o->fds) {
      list_del_owner(o);
      close(o->cfd);
      free(o);
    }
    /* Force OK on unlock-all, since it _will_ succeed once the
       owner is deleted */
    msg->error = 0;
  }

  return -msg->error;
}

#ifdef DEBUG
static uint32_t owner_hash(const unsigned char *id, size_t id_len)
{
  uint32_t h = 0;
  size_t i;
  for (i = 0; i < id_len; i++)
    h = ((h << 8) | (h >> 24)) ^ id[i];

  return h;
}
#endif

static int ulockmgr_canonicalize(int fd, struct flock *lock)
{
  off_t offset;
  if (lock->l_whence == SEEK_CUR) {
    offset = lseek(fd, 0, SEEK_CUR);
    if (offset == (off_t) -1)
      return -errno;
  } else if (lock->l_whence == SEEK_END) {
    struct stat stbuf;
    int res = fstat(fd, &stbuf);
    if (res == -1)
      return -errno;

    offset = stbuf.st_size;
  } else
    offset = 0;

  lock->l_whence = SEEK_SET;
  lock->l_start += offset;

  if (lock->l_start < 0)
    return -EINVAL;

  if (lock->l_len < 0) {
    lock->l_start += lock->l_len;
    if (lock->l_start < 0)
      return -EINVAL;
    lock->l_len = -lock->l_len;
  }
  if (lock->l_len && lock->l_start + lock->l_len - 1 < 0)
    return -EINVAL;

  return 0;
}

int ulockmgr_op(int fd, int cmd, struct flock *lock, const void *owner,
		size_t owner_len)
{
  int err;
  struct message msg;
  sigset_t old;
  sigset_t block;

  if (cmd != F_GETLK && cmd != F_SETLK && cmd != F_SETLKW)
    return -EINVAL;

  if (lock->l_type != F_RDLCK && lock->l_type != F_WRLCK &&
      lock->l_type != F_UNLCK)
    return -EINVAL;

  if (lock->l_whence != SEEK_SET && lock->l_whence != SEEK_CUR &&
      lock->l_whence != SEEK_END)
    return -EINVAL;

#ifdef DEBUG
  fprintf(stderr, "libulockmgr: %i %i %i %lli %lli own: 0x%08x\n",
          cmd, lock->l_type, lock->l_whence, lock->l_start, lock->l_len,
          owner_hash(owner, owner_len));
#endif

  /* Unlock should never block anyway */
  if (cmd == F_SETLKW && lock->l_type == F_UNLCK)
    cmd = F_SETLK;

  memset(&msg, 0, sizeof(struct message));
  msg.cmd = cmd;
  msg.fd = fd;
  msg.lock = *lock;
  err = ulockmgr_canonicalize(fd, &msg.lock);
  if (err)
    return err;

  sigemptyset(&block);
  sigaddset(&block, SIGUSR1);
  pthread_sigmask(SIG_BLOCK, &block, &old);
  pthread_mutex_lock(&ulockmgr_lock);
  err = ulockmgr_send_request(&msg, owner, owner_len);
  pthread_mutex_unlock(&ulockmgr_lock);
  pthread_sigmask(SIG_SETMASK, &old, NULL);
  if (!err && cmd == F_GETLK) {
    if (msg.lock.l_type == F_UNLCK)
      lock->l_type = F_UNLCK;
    else
      *lock = msg.lock;
  }

  return err;
}