File: dotlock.c

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/* dotlock.c - dotfile locking
 * Copyright (C) 1998, 2000, 2001, 2003, 2004,
 *               2005, 2006, 2008 Free Software Foundation, Inc.
 *
 * This file is part of JNLIB.
 *
 * JNLIB is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * JNLIB is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <errno.h>
#include <unistd.h>
#ifdef  HAVE_DOSISH_SYSTEM
# define WIN32_LEAN_AND_MEAN
# include <windows.h>
#else
# include <sys/utsname.h>
#endif
#include <sys/types.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>

#include "libjnlib-config.h"
#include "stringhelp.h"
#include "dotlock.h"

#if !defined(DIRSEP_C) && !defined(EXTSEP_C) \
    && !defined(DIRSEP_S) && !defined(EXTSEP_S)
#ifdef HAVE_DOSISH_SYSTEM
#define DIRSEP_C '\\'
#define EXTSEP_C '.'
#define DIRSEP_S "\\"
#define EXTSEP_S "."
#else
#define DIRSEP_C '/'
#define EXTSEP_C '.'
#define DIRSEP_S "/"
#define EXTSEP_S "."
#endif
#endif


/* The object describing a lock.  */
struct dotlock_handle
{
  struct dotlock_handle *next;
  char *lockname;      /* Name of the actual lockfile.          */
  int locked;          /* Lock status.                          */
  int disable;         /* If true, locking is disabled.         */

#ifdef HAVE_DOSISH_SYSTEM
  HANDLE lockhd;       /* The W32 handle of the lock file.      */
#else
  char *tname;         /* Name of the lockfile template.        */
  size_t nodename_off; /* Offset in TNAME of the nodename part. */
  size_t nodename_len; /* Length of the nodename part.          */
#endif /* HAVE_DOSISH_SYSTEM */
};


/* A list of of all lock handles. */
static volatile DOTLOCK all_lockfiles;

/* If this has the value true all locking is disabled.  */
static int never_lock;


/* Local protototypes.  */
#ifndef HAVE_DOSISH_SYSTEM
static int read_lockfile (DOTLOCK h, int *same_node);
#endif /*!HAVE_DOSISH_SYSTEM*/




/* Entirely disable all locking.  This function should be called
   before any locking is done.  It may be called right at startup of
   the process as it only sets a global value.  */
void
disable_dotlock(void)
{
  never_lock = 1;
}



/* Create a lockfile for a file name FILE_TO_LOCK and returns an
   object of type DOTLOCK which may be used later to actually acquire
   the lock.  A cleanup routine gets installed to cleanup left over
   locks or other files used internally by the lock mechanism.

   Calling this function with NULL does only install the atexit
   handler and may thus be used to assure that the cleanup is called
   after all other atexit handlers.

   This function creates a lock file in the same directory as
   FILE_TO_LOCK using that name and a suffix of ".lock".  Note that on
   POSIX systems a temporary file ".#lk.<hostname>.pid[.threadid] is
   used.

   The function returns an new handle which needs to be released using
   destroy_dotlock but gets also released at the termination of the
   process.  On error NULL is returned.
 */
DOTLOCK
create_dotlock (const char *file_to_lock)
{
  static int initialized;
  DOTLOCK h;
#ifndef  HAVE_DOSISH_SYSTEM
  int  fd = -1;
  char pidstr[16];
  const char *nodename;
  const char *dirpart;
  int dirpartlen;
  struct utsname utsbuf;
  size_t tnamelen;
#endif

  if ( !initialized )
    {
      atexit (dotlock_remove_lockfiles);
      initialized = 1;
    }

  if ( !file_to_lock )
    return NULL;  /* Only initialization was requested.  */

  h = jnlib_calloc (1, sizeof *h);
  if (!h)
    return NULL;

  if (never_lock)
    {
      h->disable = 1;
#ifdef _REENTRANT
      /* fixme: aquire mutex on all_lockfiles */
#endif
      h->next = all_lockfiles;
      all_lockfiles = h;
      return h;
    }

#ifndef HAVE_DOSISH_SYSTEM
  /*
     This is the POSIX version which uses a temporary file and the
     link system call to make locking an atomic operation.
   */

  snprintf (pidstr, sizeof pidstr, "%10d\n", (int)getpid() );

  /* Create a temporary file. */
  if ( uname ( &utsbuf ) )
    nodename = "unknown";
  else
    nodename = utsbuf.nodename;

#ifdef __riscos__
  {
    char *iter = (char *) nodename;
    for (; iter[0]; iter++)
      if (iter[0] == '.')
        iter[0] = '/';
  }
#endif /* __riscos__ */

  if ( !(dirpart = strrchr (file_to_lock, DIRSEP_C)) )
    {
      dirpart = EXTSEP_S;
      dirpartlen = 1;
    }
  else
    {
      dirpartlen = dirpart - file_to_lock;
      dirpart = file_to_lock;
    }

#ifdef _REENTRANT
    /* fixme: aquire mutex on all_lockfiles */
#endif
  h->next = all_lockfiles;
  all_lockfiles = h;

  tnamelen = dirpartlen + 6 + 30 + strlen(nodename) + 10;
  h->tname = jnlib_malloc (tnamelen + 1);
  if (!h->tname)
    {
      all_lockfiles = h->next;
      jnlib_free (h);
      return NULL;
    }
  h->nodename_len = strlen (nodename);

#ifndef __riscos__
  snprintf (h->tname, tnamelen, "%.*s/.#lk%p.", dirpartlen, dirpart, h );
  h->nodename_off = strlen (h->tname);
  snprintf (h->tname+h->nodename_off, tnamelen - h->nodename_off,
           "%s.%d", nodename, (int)getpid ());
#else /* __riscos__ */
  snprintf (h->tname, tnamelen, "%.*s.lk%p/", dirpartlen, dirpart, h );
  h->nodename_off = strlen (h->tname);
  snprintf (h->tname+h->nodename_off, tnamelen - h->modename_off,
            "%s/%d", nodename, (int)getpid () );
#endif /* __riscos__ */

  do
    {
      errno = 0;
      fd = open (h->tname, O_WRONLY|O_CREAT|O_EXCL,
                 S_IRUSR|S_IRGRP|S_IROTH|S_IWUSR );
    }
  while (fd == -1 && errno == EINTR);

  if ( fd == -1 )
    {
      all_lockfiles = h->next;
      log_error (_("failed to create temporary file `%s': %s\n"),
                  h->tname, strerror(errno));
      jnlib_free (h->tname);
      jnlib_free (h);
      return NULL;
    }
  if ( write (fd, pidstr, 11 ) != 11 )
    goto write_failed;
  if ( write (fd, nodename, strlen (nodename) ) != strlen (nodename) )
    goto write_failed;
  if ( write (fd, "\n", 1 ) != 1 )
    goto write_failed;
  if ( close (fd) )
    {
      if ( errno == EINTR )
        fd = -1;
      goto write_failed;
    }
  fd = -1;

# ifdef _REENTRANT
  /* release mutex */
# endif
  h->lockname = jnlib_malloc ( strlen (file_to_lock) + 6 );
  if (!h->lockname)
    {
      all_lockfiles = h->next;
      unlink (h->tname);
      jnlib_free (h->tname);
      jnlib_free (h);
      return NULL;
    }
  strcpy (stpcpy (h->lockname, file_to_lock), EXTSEP_S "lock");
  return h;

 write_failed:
  all_lockfiles = h->next;
# ifdef _REENTRANT
  /* fixme: release mutex */
# endif
  log_error ( _("error writing to `%s': %s\n"), h->tname, strerror(errno) );
  if (fd != -1)
    close (fd);
  unlink (h->tname);
  jnlib_free (h->tname);
  jnlib_free (h);
  return NULL;

#else /* HAVE_DOSISH_SYSTEM */

  /* The Windows version does not need a temporary file but uses the
     plain lock file along with record locking.  We create this file
     here so that we later do only need to do the file locking.  For
     error reporting it is useful to keep the name of the file in the
     handle.  */
  h->next = all_lockfiles;
  all_lockfiles = h;

  h->lockname = jnlib_malloc ( strlen (file_to_lock) + 6 );
  if (!h->lockname)
    {
      all_lockfiles = h->next;
      jnlib_free (h);
      return NULL;
    }
  strcpy (stpcpy(h->lockname, file_to_lock), EXTSEP_S "lock");

  /* If would be nice if we would use the FILE_FLAG_DELETE_ON_CLOSE
     along with FILE_SHARE_DELETE but that does not work due to a race
     condition: Despite the OPEN_ALWAYS flag CreateFile may return an
     error and we can't reliable create/open the lock file unless we
     would wait here until it works - however there are other valid
     reasons why a lock file can't be created and thus the process
     would not stop as expected but spin til until Windows crashes.
     Our solution is to keep the lock file open; that does not
     harm. */
  h->lockhd = CreateFile (h->lockname,
                          GENERIC_READ|GENERIC_WRITE,
                          FILE_SHARE_READ|FILE_SHARE_WRITE,
                          NULL, OPEN_ALWAYS, 0, NULL);
  if (h->lockhd == INVALID_HANDLE_VALUE)
    {
      log_error (_("can't create `%s': %s\n"), h->lockname, w32_strerror (-1));
      all_lockfiles = h->next;
      jnlib_free (h->lockname);
      jnlib_free (h);
      return NULL;
    }
  return h;

#endif /* HAVE_DOSISH_SYSTEM */
}


/* Destroy the local handle H and release the lock. */
void
destroy_dotlock ( DOTLOCK h )
{
  DOTLOCK hprev, htmp;

  if ( !h )
    return;

  /* First remove the handle from our global list of all locks. */
  for (hprev=NULL, htmp=all_lockfiles; htmp; hprev=htmp, htmp=htmp->next)
    if (htmp == h)
      {
        if (hprev)
          hprev->next = htmp->next;
        else
          all_lockfiles = htmp->next;
        h->next = NULL;
        break;
      }

  /* Then destroy the lock. */
  if (!h->disable)
    {
#ifdef HAVE_DOSISH_SYSTEM
      if (h->locked)
        {
          UnlockFile (h->lockhd, 0, 0, 1, 0);
        }
      CloseHandle (h->lockhd);
#else /* !HAVE_DOSISH_SYSTEM */
      if (h->locked && h->lockname)
        unlink (h->lockname);
      if (h->tname)
        unlink (h->tname);
      jnlib_free (h->tname);
#endif /* HAVE_DOSISH_SYSTEM */
      jnlib_free (h->lockname);
    }
  jnlib_free(h);
}


#ifndef HAVE_DOSISH_SYSTEM
static int
maybe_deadlock( DOTLOCK h )
{
  DOTLOCK r;

  for ( r=all_lockfiles; r; r = r->next )
    {
      if ( r != h && r->locked )
        return 1;
    }
  return 0;
}
#endif /*!HAVE_DOSISH_SYSTEM*/



/* Do a lock on H. A TIMEOUT of 0 returns immediately, -1 waits
   forever (hopefully not), other values are reserved (should then be
   timeouts in milliseconds).  Returns: 0 on success  */
int
make_dotlock ( DOTLOCK h, long timeout )
{
  int backoff = 0;
#ifndef HAVE_DOSISH_SYSTEM
  int  pid;
  const char *maybe_dead="";
  int same_node;
#endif /*!HAVE_DOSISH_SYSTEM*/

  if ( h->disable )
    return 0; /* Locks are completely disabled.  Return success. */

  if ( h->locked )
    {
#ifndef __riscos__
      log_debug ("Oops, `%s' is already locked\n", h->lockname);
#endif /* !__riscos__ */
      return 0;
    }

  for (;;)
    {
#ifndef HAVE_DOSISH_SYSTEM
# ifndef __riscos__
      if ( !link(h->tname, h->lockname) )
        {
          /* fixme: better use stat to check the link count */
          h->locked = 1;
          return 0; /* okay */
	}
      if ( errno != EEXIST )
        {
          log_error ( "lock not made: link() failed: %s\n", strerror(errno) );
          return -1;
	}
# else /* __riscos__ */
      if ( !renamefile(h->tname, h->lockname) )
        {
          h->locked = 1;
          return 0; /* okay */
        }
      if ( errno != EEXIST )
        {
          log_error( "lock not made: rename() failed: %s\n", strerror(errno) );
          return -1;
        }
# endif /* __riscos__ */

      if ( (pid = read_lockfile (h, &same_node)) == -1 )
        {
          if ( errno != ENOENT )
            {
              log_info ("cannot read lockfile\n");
              return -1;
	    }
          log_info( "lockfile disappeared\n");
          continue;
	}
      else if ( pid == getpid() && same_node )
        {
          log_info( "Oops: lock already held by us\n");
          h->locked = 1;
          return 0; /* okay */
	}
      else if ( same_node && kill (pid, 0) && errno == ESRCH )
        {
# ifndef __riscos__
          log_info (_("removing stale lockfile (created by %d)\n"), pid );
          unlink (h->lockname);
          continue;
# else /* __riscos__ */
          /* Under RISCOS we are *pretty* sure that the other task
             is dead and therefore we remove the stale lock file. */
          maybe_dead = _(" - probably dead - removing lock");
          unlink(h->lockname);
# endif /* __riscos__ */
	}

      if ( timeout == -1 )
        {
          /* Wait until lock has been released. */
          struct timeval tv;

          log_info (_("waiting for lock (held by %d%s) %s...\n"),
                    pid, maybe_dead, maybe_deadlock(h)? _("(deadlock?) "):"");


          /* We can't use sleep, cause signals may be blocked. */
          tv.tv_sec = 1 + backoff;
          tv.tv_usec = 0;
          select(0, NULL, NULL, NULL, &tv);
          if ( backoff < 10 )
            backoff++ ;
	}
      else
        return -1;
#else /*HAVE_DOSISH_SYSTEM*/
      int w32err;

      if (LockFile (h->lockhd, 0, 0, 1, 0))
        {
          h->locked = 1;
          return 0; /* okay */
        }
      w32err = GetLastError ();
      if (w32err != ERROR_LOCK_VIOLATION)
        {
          log_error (_("lock `%s' not made: %s\n"),
                     h->lockname, w32_strerror (w32err));
          return -1;
        }

      if ( timeout == -1 )
        {
          /* Wait until lock has been released. */
          log_info (_("waiting for lock %s...\n"), h->lockname);
          Sleep ((1 + backoff)*1000);
          if ( backoff < 10 )
            backoff++ ;
	}
      else
        return -1;
#endif /*HAVE_DOSISH_SYSTEM*/
    }
  /*NOTREACHED*/
}


/* Release a lock.  Returns 0 on success.  */
int
release_dotlock( DOTLOCK h )
{
#ifndef HAVE_DOSISH_SYSTEM
  int pid, same_node;
#endif

  /* To avoid atexit race conditions we first check whether there are
     any locks left.  It might happen that another atexit handler
     tries to release the lock while the atexit handler of this module
     already ran and thus H is undefined.  */
  if (!all_lockfiles)
    return 0;

  if ( h->disable )
    return 0;

  if ( !h->locked )
    {
      log_debug("Oops, `%s' is not locked\n", h->lockname);
      return 0;
    }

#ifdef HAVE_DOSISH_SYSTEM
  if (!UnlockFile (h->lockhd, 0, 0, 1, 0))
    {
      log_error ("release_dotlock: error removing lockfile `%s': %s\n",
                 h->lockname, w32_strerror (-1));
      return -1;
    }
#else

  pid = read_lockfile (h, &same_node);
  if ( pid == -1 )
    {
      log_error( "release_dotlock: lockfile error\n");
      return -1;
    }
  if ( pid != getpid() || !same_node )
    {
      log_error( "release_dotlock: not our lock (pid=%d)\n", pid);
      return -1;
    }

#ifndef __riscos__
  if ( unlink( h->lockname ) )
    {
      log_error ("release_dotlock: error removing lockfile `%s'\n",
                 h->lockname);
      return -1;
    }
  /* Fixme: As an extra check we could check whether the link count is
     now really at 1. */
#else /* __riscos__ */
  if ( renamefile (h->lockname, h->tname) )
    {
      log_error ("release_dotlock: error renaming lockfile `%s' to `%s'\n",
                 h->lockname, h->tname);
      return -1;
    }
#endif /* __riscos__ */

#endif /* !HAVE_DOSISH_SYSTEM */
  h->locked = 0;
  return 0;
}


/* Read the lock file and return the pid, returns -1 on error.  True
   will be stored in the integer at address SAME_NODE if the lock file
   has been created on the same node. */
#ifndef HAVE_DOSISH_SYSTEM
static int
read_lockfile (DOTLOCK h, int *same_node )
{
  char buffer_space[10+1+70+1]; /* 70 is just an estimated value; node
                                   name are usually shorter. */
  int fd;
  int pid = -1;
  char *buffer, *p;
  size_t expected_len;
  int res, nread;

  *same_node = 0;
  expected_len = 10 + 1 + h->nodename_len + 1;
  if ( expected_len >= sizeof buffer_space)
    {
      buffer = jnlib_malloc (expected_len);
      if (!buffer)
        return -1;
    }
  else
    buffer = buffer_space;

  if ( (fd = open (h->lockname, O_RDONLY)) == -1 )
    {
      int e = errno;
      log_info ("error opening lockfile `%s': %s\n",
                h->lockname, strerror(errno) );
      if (buffer != buffer_space)
        jnlib_free (buffer);
      errno = e; /* Need to return ERRNO here. */
      return -1;
    }

  p = buffer;
  nread = 0;
  do
    {
      res = read (fd, p, expected_len - nread);
      if (res == -1 && errno == EINTR)
        continue;
      if (res < 0)
        {
          log_info ("error reading lockfile `%s'", h->lockname );
          close (fd);
          if (buffer != buffer_space)
            jnlib_free (buffer);
          errno = 0; /* Do not return an inappropriate ERRNO. */
          return -1;
        }
      p += res;
      nread += res;
    }
  while (res && nread != expected_len);
  close(fd);

  if (nread < 11)
    {
      log_info ("invalid size of lockfile `%s'", h->lockname );
      if (buffer != buffer_space)
        jnlib_free (buffer);
      errno = 0; /* Better don't return an inappropriate ERRNO. */
      return -1;
    }

  if (buffer[10] != '\n'
      || (buffer[10] = 0, pid = atoi (buffer)) == -1
#ifndef __riscos__
      || !pid
#else /* __riscos__ */
      || (!pid && riscos_getpid())
#endif /* __riscos__ */
      )
    {
      log_error ("invalid pid %d in lockfile `%s'", pid, h->lockname );
      if (buffer != buffer_space)
        jnlib_free (buffer);
      errno = 0;
      return -1;
    }

  if (nread == expected_len
      && !memcmp (h->tname+h->nodename_off, buffer+11, h->nodename_len)
      && buffer[11+h->nodename_len] == '\n')
    *same_node = 1;

  if (buffer != buffer_space)
    jnlib_free (buffer);
  return pid;
}
#endif /* !HAVE_DOSISH_SYSTEM */


/* Remove all lockfiles.  This is usually called by the atexit handler
   installed by this module but may also be called by other
   termination handlers.  */
void
dotlock_remove_lockfiles()
{
  DOTLOCK h, h2;

  h = all_lockfiles;
  all_lockfiles = NULL;

  while ( h )
    {
      h2 = h->next;
      destroy_dotlock (h);
      h = h2;
    }
}