Initial revision

src/filelock.c

+/* Copyright (C) 1985, 1986, 1987 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 1, or (at your option)
+any later version.
+
+GNU Emacs 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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs; see the file COPYING.  If not, write to
+the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include "config.h"
+#include <pwd.h>
+#include <errno.h>
+#include <sys/file.h>
+#ifdef USG
+#include <fcntl.h>
+#endif /* USG */
+
+#undef NULL
+#include "lisp.h"
+#include "paths.h"
+#include "buffer.h"
+
+extern int errno;
+
+#ifdef CLASH_DETECTION
+  
+/* If system does not have symbolic links, it does not have lstat.
+   In that case, use ordinary stat instead.  */
+
+#ifndef S_IFLNK
+#define lstat stat
+#endif
+
+static Lisp_Object
+lock_file_owner_name (lfname)
+     char *lfname;
+{
+  struct stat s;
+  struct passwd *the_pw;
+  extern struct passwd *getpwuid ();
+
+  if (lstat (lfname, &s) == 0)
+    the_pw = getpwuid (s.st_uid);
+  return (the_pw == 0 ? Qnil : build_string (the_pw->pw_name));
+}
+
+
+/* lock_file locks file fn,
+   meaning it serves notice on the world that you intend to edit that file.
+   This should be done only when about to modify a file-visiting
+   buffer previously unmodified.
+   Do not (normally) call lock_buffer for a buffer already modified,
+   as either the file is already locked, or the user has already
+   decided to go ahead without locking.
+
+   When lock_buffer returns, either the lock is locked for us,
+   or the user has said to go ahead without locking.
+
+   If the file is locked by someone else, lock_buffer calls
+   ask-user-about-lock (a Lisp function) with two arguments,
+   the file name and the name of the user who did the locking.
+   This function can signal an error, or return t meaning
+   take away the lock, or return nil meaning ignore the lock.  */
+
+/* The lock file name is the file name with "/" replaced by "!"
+   and put in the Emacs lock directory.  */
+/* (ie., /ka/king/junk.tex -> /!/!ka!king!junk.tex). */
+
+void
+lock_file (fn)
+     register Lisp_Object fn;
+{
+  register Lisp_Object attack;
+  register char *lfname;
+
+  /* Create the name of the lock-file for file fn */
+  lfname = (char *) alloca (XSTRING (fn)->size + strlen (PATH_LOCK) + 1);
+  fill_in_lock_file_name (lfname, fn);
+
+  /* See if this file is visited and has changed on disk since it was visited.  */
+  {
+    register Lisp_Object subject_buf = Fget_file_buffer (fn);
+    if (!NULL (subject_buf)
+	&& NULL (Fverify_visited_file_modtime (subject_buf))
+	&& !NULL (Ffile_exists_p (fn)))
+      call1 (intern ("ask-user-about-supersession-threat"), fn);
+  }
+
+  /* Try to lock the lock. */
+  if (lock_if_free (lfname) <= 0)
+    /* Return now if we have locked it, or if lock dir does not exist */
+    return;
+
+  /* Else consider breaking the lock */
+  attack = call2 (intern ("ask-user-about-lock"), fn,
+		  lock_file_owner_name (lfname));
+  if (!NULL (attack))
+    /* User says take the lock */
+    {
+      lock_superlock (lfname);
+      lock_file_1 (lfname, O_WRONLY) ;
+      unlink (PATH_SUPERLOCK);
+      return;
+    }
+  /* User says ignore the lock */
+}
+
+fill_in_lock_file_name (lockfile, fn)
+     register char *lockfile;
+     register Lisp_Object fn;
+{
+  register char *p;
+
+  strcpy (lockfile, PATH_LOCK);
+
+  p = lockfile + strlen (lockfile);
+
+  strcpy (p, XSTRING (fn)->data);
+
+  for (; *p; p++)
+    {
+      if (*p == '/')
+	*p = '!';
+    }
+}
+
+/* Lock the lock file named LFNAME.
+   If MODE is O_WRONLY, we do so even if it is already locked.
+   If MODE is O_WRONLY | O_EXCL | O_CREAT, we do so only if it is free.
+   Return 1 if successful, 0 if not.  */
+
+int
+lock_file_1 (lfname, mode)
+     int mode; char *lfname; 
+{
+  register int fd;
+  char buf[20];
+
+  if ((fd = open (lfname, mode, 0666)) >= 0)
+    {
+#ifdef USG
+      chmod (lfname, 0666);
+#else
+      fchmod (fd, 0666);
+#endif
+      sprintf (buf, "%d ", getpid ());
+      write (fd, buf, strlen (buf));
+      close (fd);
+      return 1;
+    }
+  else
+    return 0;
+}
+
+/* Lock the lock named LFNAME if possible.
+   Return 0 in that case.
+   Return positive if lock is really locked by someone else.
+   Return -1 if cannot lock for any other reason.  */
+
+int
+lock_if_free (lfname)
+     register char *lfname; 
+{
+  register int clasher;
+
+  while (lock_file_1 (lfname, O_WRONLY | O_EXCL | O_CREAT) == 0)
+    {
+      if (errno != EEXIST)
+	return -1;
+      clasher = current_lock_owner (lfname);
+      if (clasher != 0)
+	if (clasher != getpid ())
+	  return (clasher);
+	else return (0);
+      /* Try again to lock it */
+    }
+  return 0;
+}
+
+/* Return the pid of the process that claims to own the lock file LFNAME,
+   or 0 if nobody does or the lock is obsolete,
+   or -1 if something is wrong with the locking mechanism.  */
+
+int
+current_lock_owner (lfname)
+     char *lfname;
+{
+  int owner = current_lock_owner_1 (lfname);
+  if (owner == 0 && errno == ENOENT)
+    return (0);
+  /* Is it locked by a process that exists?  */
+  if (owner != 0 && (kill (owner, 0) >= 0 || errno == EPERM))
+    return (owner);
+  if (unlink (lfname) < 0)
+    return (-1);
+  return (0);
+}
+
+int
+current_lock_owner_1 (lfname)
+     char *lfname;
+{
+  register int fd;
+  char buf[20];
+  int tem;
+
+  fd = open (lfname, O_RDONLY, 0666);
+  if (fd < 0)
+    return 0;
+  tem = read (fd, buf, sizeof buf);
+  close (fd);
+  return (tem <= 0 ? 0 : atoi (buf));
+}
+
+
+void
+unlock_file (fn)
+     register Lisp_Object fn;
+{
+  register char *lfname;
+
+  lfname = (char *) alloca (XSTRING (fn)->size + strlen (PATH_LOCK) + 1);
+  fill_in_lock_file_name (lfname, fn);
+
+  lock_superlock (lfname);
+
+  if (current_lock_owner_1 (lfname) == getpid ())
+    unlink (lfname);
+
+  unlink (PATH_SUPERLOCK);
+}
+
+lock_superlock (lfname)
+     char *lfname;
+{
+  register int i, fd;
+
+  for (i = -20; i < 0 && (fd = open (PATH_SUPERLOCK,
+				     O_WRONLY | O_EXCL | O_CREAT, 0666)) < 0;
+       i++)
+    {
+      if (errno != EEXIST)
+	return;
+      sleep (1);
+    }
+  if (fd >= 0)
+    {
+#ifdef USG
+      chmod (PATH_SUPERLOCK, 0666);
+#else
+      fchmod (fd, 0666);
+#endif
+      write (fd, lfname, strlen (lfname));
+      close (fd);
+    }
+}
+
+void
+unlock_all_files ()
+{
+  register Lisp_Object tail;
+  register struct buffer *b;
+
+  for (tail = Vbuffer_alist; XGCTYPE (tail) == Lisp_Cons;
+       tail = XCONS (tail)->cdr)
+    {
+      b = XBUFFER (XCONS (XCONS (tail)->car)->cdr);
+      if (XTYPE (b->filename) == Lisp_String &&
+	  b->save_modified < BUF_MODIFF (b))
+	unlock_file (b->filename);
+    }
+}
+
+
+DEFUN ("lock-buffer", Flock_buffer, Slock_buffer,
+  0, 1, 0,
+  "Lock FILE, if current buffer is modified.\n\
+FILE defaults to current buffer's visited file,\n\
+or else nothing is done if current buffer isn't visiting a file.")
+  (fn)
+     Lisp_Object fn;
+{
+  if (NULL (fn))
+    fn = current_buffer->filename;
+  else
+    CHECK_STRING (fn, 0);
+  if (current_buffer->save_modified < MODIFF
+      && !NULL (fn))
+    lock_file (fn);
+  return Qnil;    
+}
+
+DEFUN ("unlock-buffer", Funlock_buffer, Sunlock_buffer,
+  0, 0, 0,
+ "Unlock the file visited in the current buffer,\n\
+if it should normally be locked.")
+  ()
+{
+  if (current_buffer->save_modified < MODIFF &&
+      XTYPE (current_buffer->filename) == Lisp_String)
+    unlock_file (current_buffer->filename);
+  return Qnil;
+}
+
+
+/* Unlock the file visited in buffer BUFFER.  */
+
+unlock_buffer (buffer)
+     struct buffer *buffer;
+{
+  if (buffer->save_modified < BUF_MODIFF (buffer) &&
+      XTYPE (buffer->filename) == Lisp_String)
+    unlock_file (buffer->filename);
+}
+
+DEFUN ("file-locked-p", Ffile_locked_p, Sfile_locked_p, 0, 1, 0,
+  "Return nil if the FILENAME is not locked,\n\
+t if it is locked by you, else a string of the name of the locker.")
+  (fn)
+  Lisp_Object fn;
+{
+  register char *lfname;
+  int owner;
+
+  fn = Fexpand_file_name (fn, Qnil);
+
+  /* Create the name of the lock-file for file filename */
+  lfname = (char *) alloca (XSTRING (fn)->size + strlen (PATH_LOCK) + 1);
+  fill_in_lock_file_name (lfname, fn);
+
+  owner = current_lock_owner (lfname);
+  if (owner <= 0)
+    return (Qnil);
+  else if (owner == getpid ())
+    return (Qt);
+  
+  return (lock_file_owner_name (lfname));
+}
+
+syms_of_filelock ()
+{
+  defsubr (&Sunlock_buffer);
+  defsubr (&Slock_buffer);
+  defsubr (&Sfile_locked_p);
+}
+
+#endif /* CLASH_DETECTION */