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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>

00024 struct message {
      unsigned intr : 1;
      unsigned nofd : 1;
      pthread_t thr;
      int cmd;
      int fd;
      struct flock lock;
      int error;
};

00034 struct fd_store {
      struct fd_store *next;
      int fd;
      int inuse;
};

00040 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;
}

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