Re: [PATCH update3] Support for filesystem watching (inotify)

["Rüdiger Sonderfeld" <ruediger@c-plusplus.de>]

On Sunday 05 June 2011 07:45:58 Eli Zaretskii wrote:
> > From: Rüdiger Sonderfeld <ruediger@c-plusplus.de>
> > Date: Sun, 5 Jun 2011 01:36:35 +0200
> > 
> > > In general, you should not call Lisp from the read fd callback.
> > > Recursive calls into Lisp may fail. Instead post a Lisp event and
> > > handle it in keyboard.c and some Lisp code.
> > 
> > Thanks for your advise. I changed the code to use events.
> 
> You did?  Did you send the correct patch?

Oh. This should be the correct patch.

Subject: [PATCH] Added basic file system watching support.

It currently only works with inotify/Linux. It adds file-watch and file-unwatch functions.
---
 configure.in      |   14 +++
 lisp/filewatch.el |   54 ++++++++++
 src/Makefile.in   |    2 +-
 src/emacs.c       |    4 +
 src/filewatch.c   |  305 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/keyboard.c    |   28 +++++
 src/lisp.h        |    5 +
 src/termhooks.h   |    5 +
 8 files changed, 416 insertions(+), 1 deletions(-)
 create mode 100644 lisp/filewatch.el
 create mode 100644 src/filewatch.c

diff --git a/configure.in b/configure.in
index 06880ea..5696fa2 100644
--- a/configure.in
+++ b/configure.in
@@ -169,6 +169,7 @@ OPTION_DEFAULT_ON([dbus],[don't compile with D-Bus support])
 OPTION_DEFAULT_ON([gconf],[don't compile with GConf support])
 OPTION_DEFAULT_ON([selinux],[don't compile with SELinux support])
 OPTION_DEFAULT_ON([gnutls],[don't use -lgnutls for SSL/TLS support])
+OPTION_DEFAULT_ON([inotify],[don't compile with inotify (file-watch) support])
 
 ## For the times when you want to build Emacs but don't have
 ## a suitable makeinfo, and can live without the manuals.
@@ -1981,6 +1982,19 @@ fi
 AC_SUBST(LIBGNUTLS_LIBS)
 AC_SUBST(LIBGNUTLS_CFLAGS)
 
+dnl inotify is only available on GNU/Linux.
+HAVE_INOTIFY=no
+if test "${with_inotify}" = "yes"; then
+   AC_CHECK_HEADERS(sys/inotify.h)
+   if test "$ac_cv_header_sys_inotify_h" = yes ; then
+     AC_CHECK_FUNCS(inotify_init1 inotify_add_watch inotify_rm_watch, HAVE_INOTIFY=yes)
+   fi
+fi
+if test "${HAVE_INOTIFY}" = "yes"; then
+   AC_DEFINE(HAVE_INOTIFY, [1], [Define to 1 to use inotify])
+   AC_DEFINE(HAVE_FILEWATCH, [1], [Define to 1 to support filewatch])
+fi
+
 dnl Do not put whitespace before the #include statements below.
 dnl Older compilers (eg sunos4 cc) choke on it.
 HAVE_XAW3D=no
diff --git a/lisp/filewatch.el b/lisp/filewatch.el
new file mode 100644
index 0000000..2c97589
--- /dev/null
+++ b/lisp/filewatch.el
@@ -0,0 +1,54 @@
+;;; filewatch.el --- Elisp support for watching filesystem events.
+
+;; Copyright (C) 2011 Free Software Foundation, Inc.
+
+;; Author: Rüdiger Sonderfeld <ruediger@c-plusplus.de>
+;; Keywords: files
+
+;; 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 3 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This file contains the elisp part of the filewatch API.
+
+;;; Code:
+
+(eval-when-compile
+  (require 'cl))
+
+(defun filewatch-event-p (event)
+  "Check if EVENT is a filewatch event."
+  (and (listp event)
+       (eq (car event) 'filewatch-event)))
+
+;;;###autoload
+(defun filewatch-handle-event (event)
+  "Handle file system monitoring event.
+If EVENT is a filewatch event then the callback is called.  If EVENT is
+not a filewatch event then a `filewatch-error' is signaled."
+  (interactive "e")
+
+  (unless (filewatch-event-p event)
+    (signal 'filewatch-error (cons "Not a valid filewatch event" event)))
+
+  (loop for ev in (cdr event)
+     unless (and (listp ev) (>= (length ev) 3))
+     do (signal 'filewatch-error (cons "Not a valid filewatch event" event))
+     do (funcall (cadr ev) (car ev) (caddr ev))))
+
+(provide 'filewatch)
+
+;;; filewatch.el ends here
diff --git a/src/Makefile.in b/src/Makefile.in
index c4250b9..9135e7d 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -334,7 +334,7 @@ base_obj = dispnew.o frame.o scroll.o xdisp.o menu.o $(XMENU_OBJ) window.o \
 	syntax.o $(UNEXEC_OBJ) bytecode.o \
 	process.o gnutls.o callproc.o \
 	region-cache.o sound.o atimer.o \
-	doprnt.o intervals.o textprop.o composite.o xml.o \
+	doprnt.o intervals.o textprop.o composite.o xml.o filewatch.o \
 	$(MSDOS_OBJ) $(MSDOS_X_OBJ) $(NS_OBJ) $(CYGWIN_OBJ) $(FONT_OBJ)
 obj = $(base_obj) $(NS_OBJC_OBJ)
 
diff --git a/src/emacs.c b/src/emacs.c
index 3a7c5c0..fb734e5 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -1558,6 +1558,10 @@ main (int argc, char **argv)
       syms_of_gnutls ();
 #endif
 
+#ifdef HAVE_FILEWATCH
+      syms_of_filewatch ();
+#endif /* HAVE_FILEWATCH */
+
 #ifdef HAVE_DBUS
       syms_of_dbusbind ();
 #endif /* HAVE_DBUS */
diff --git a/src/filewatch.c b/src/filewatch.c
new file mode 100644
index 0000000..56b79b7
--- /dev/null
+++ b/src/filewatch.c
@@ -0,0 +1,305 @@
+/* Watching file system changes.
+
+Copyright (C) 2011
+  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 3 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#ifdef HAVE_FILEWATCH
+#include <setjmp.h> /* Required for lisp.h.  */
+#include "lisp.h"
+#include "coding.h"
+#include "process.h"
+#include "keyboard.h"
+#include "character.h"
+#include "frame.h" /* Required for termhooks.h.  */
+#include "termhooks.h"
+
+static Lisp_Object Qmodify, Qmove, Qattrib, Qdelete, Qfrom, Qto, Qunkown_aspect;
+
+#ifdef HAVE_INOTIFY
+#include <sys/inotify.h>
+#include <sys/ioctl.h>
+
+enum { uninitialized = -100 };
+/* File handle for inotify.  */
+static int inotifyfd = uninitialized;
+
+/* Assoc list of files being watched.  */
+static Lisp_Object watch_list;
+
+/* This callback is called when the FD is available FOR_READ.  The inotify
+   events are read from FD and converted into input_events.  */
+
+static void
+inotify_callback (int fd, void *_, int for_read)
+{
+  struct input_event event;
+  int to_read;
+  char *buffer;
+  ssize_t n;
+  size_t i;
+
+  if (!for_read)
+    return;
+
+  to_read = 0;
+  if (ioctl (fd, FIONREAD,  &to_read) == -1)
+    report_file_error ("Error while trying to retrieve file system events",
+                       Qnil);
+  buffer = xmalloc (to_read);
+  n = read (fd, buffer, to_read);
+  if (n < 0)
+    {
+      xfree (buffer);
+      report_file_error ("Error while trying to read file system events",
+                         Qnil);
+    }
+
+  EVENT_INIT (event);
+  event.kind = FILEWATCH_EVENT;
+  event.arg = Qnil;
+
+  i = 0;
+  while (i < (size_t)n)
+    {
+      struct inotify_event *ev = (struct inotify_event*)&buffer[i];
+
+      Lisp_Object callback = Fassoc (make_number (ev->wd), watch_list);
+      if (!NILP (callback))
+        {
+          size_t len;
+          Lisp_Object name, events, event_info;
+
+          /* If a directory is watched name contains the name
+             of the file that was changed.  */
+          len = strlen (ev->name);
+          name = make_unibyte_string (ev->name, len);
+          name = DECODE_FILE (name);
+
+          events = Qnil;
+          if (ev->mask & (IN_MODIFY|IN_CREATE) )
+            events = Fcons (Fcons (Qmodify, name), events);
+          if (ev->mask & IN_MOVE_SELF)
+            events = Fcons (Fcons (Qmove, name), events);
+          if (ev->mask & IN_MOVED_FROM)
+            events = Fcons (Fcons (Qmove,
+                                   Fcons (Qfrom,
+                                          Fcons (name,
+                                                 make_number (ev->cookie)))),
+                           events);
+          if (ev->mask & IN_MOVED_TO)
+            events = Fcons (Fcons (Qmove,
+                                   Fcons (Qto,
+                                          Fcons (name,
+                                                 make_number (ev->cookie)))),
+                           events);
+          if (ev->mask & IN_ATTRIB)
+            events = Fcons (Fcons (Qattrib, name), events);
+          if (ev->mask & (IN_DELETE|IN_DELETE_SELF) )
+            events = Fcons (Fcons (Qdelete, name), events);
+
+          if (!NILP (events))
+            {
+              Lisp_Object args[2], event_info;
+              args[0] = Fcdr (callback);
+              args[1] = Fcons (events, Qnil);
+              event_info = Fcons (Fappend (2, args), Qnil);
+              if (NILP (event.arg))
+                event.arg = event_info;
+              else
+                {
+                  args[0] = event.arg;
+                  args[1] = event_info;
+                  event.arg = Fappend (2, args);
+                }
+            }
+
+          if (ev->mask & IN_IGNORED)
+            {
+              /* Event was removed automatically: Drop it from data list.  */
+              add_to_log ("File-watch: \"%s\" will be ignored", name, Qnil);
+              watch_list = Fdelete (callback, watch_list);
+            }
+          if (ev->mask & IN_Q_OVERFLOW)
+            add_to_log ("File watch: Inotify Queue Overflow!", Qnil, Qnil);
+        }
+
+      i += sizeof (*ev) + ev->len;
+    }
+
+  if (!NILP (event.arg))
+    kbd_buffer_store_event (&event);
+
+  xfree (buffer);
+}
+
+static uint32_t
+symbol_to_inotifymask (Lisp_Object symb)
+{
+  if (EQ (symb, Qmodify))
+    return IN_MODIFY | IN_CREATE;
+  else if (EQ (symb, Qmove))
+    return IN_MOVE_SELF | IN_MOVE;
+  else if (EQ (symb, Qattrib))
+    return IN_ATTRIB;
+  else if (EQ (symb, Qdelete))
+    return IN_DELETE_SELF | IN_DELETE;
+  else if (EQ (symb, Qt))
+    return IN_MODIFY | IN_CREATE | IN_MOVE_SELF | IN_MOVE | IN_ATTRIB
+      | IN_DELETE_SELF | IN_DELETE;
+  else
+    Fsignal (Qunkown_aspect, Fcons (symb, Qnil));
+}
+
+DEFUN ("file-watch", Ffile_watch, Sfile_watch, 3, 3, 0,
+       doc: /* Arrange to call FUNC if ASPECT of FILENAME changes.
+
+ASPECT might be one of the following symbols or a list of those symbols:
+
+modify -- notify when a file is modified or created.
+
+move -- notify when a file/directory is moved.
+
+attrib -- notify when attributes change.
+
+delete -- notify when a file/directory is deleted.
+
+t -- notify for all of the above.
+
+Watching a directory is not recursive.  CALLBACK receives the events as a list
+with each list element being a list containing information about an event.  The
+first element is a flag symbol.  If a directory is watched the second element is
+the name of the file that changed.  If a file is moved from or to the directory
+the second element is either 'from or 'to and the third element is the file
+name.  A fourth element contains a numeric identifier (cookie) that can be used
+to identify matching move operations if a file is moved inside the directory.
+
+Example:
+(file-watch "foo" t #'(lambda (file event) (message "%s %s" file event)))
+
+Use `file-unwatch' to stop watching.
+
+usage: (file-watch FILENAME ASPECT CALLBACK) */)
+  (Lisp_Object file_name, Lisp_Object aspect, Lisp_Object callback)
+{
+  uint32_t mask;
+  size_t i;
+  int watchdesc;
+  Lisp_Object decoded_file_name;
+
+  CHECK_STRING (file_name);
+
+  if (inotifyfd == uninitialized)
+    {
+      inotifyfd = inotify_init1 (IN_NONBLOCK|IN_CLOEXEC);
+      if (inotifyfd == -1)
+        {
+          inotifyfd = uninitialized;
+          report_file_error ("File watching feature (inotify) is not available",
+                             Qnil);
+        }
+      watch_list = Qnil;
+      add_read_fd (inotifyfd, &inotify_callback, &watch_list);
+    }
+
+  /* Convert ASPECT into the inotify event mask.  */
+  if (CONSP (aspect))
+    {
+      Lisp_Object x = aspect;
+      mask = 0;
+      while (!NILP(x))
+        {
+          mask |= symbol_to_inotifymask (Fcar (x));
+          x = Fcdr(x);
+        }
+    }
+  else
+    mask = symbol_to_inotifymask(aspect);
+
+  decoded_file_name = ENCODE_FILE (file_name);
+  watchdesc = inotify_add_watch (inotifyfd, SSDATA (decoded_file_name), mask);
+  if (watchdesc == -1)
+    report_file_error ("Could not watch file", Fcons (file_name, Qnil));
+  /* TODO: check if file is already in the watch_list.  */
+  watch_list = Fcons (Fcons (make_number (watchdesc),
+                             Fcons (file_name, Fcons (callback, Qnil))),
+                      watch_list);
+  return Qt;
+}
+
+DEFUN ("file-unwatch", Ffile_unwatch, Sfile_unwatch, 1, 1, 0,
+       doc: /* Stop watching a file or directory.  */)
+  (Lisp_Object file_name)
+{
+  Lisp_Object cell, file_name_data;
+  Lisp_Object x = watch_list;
+
+  if (inotifyfd == uninitialized)
+    return Qnil;
+  CHECK_STRING (file_name);
+
+  while (!NILP (x))
+    {
+      cell = Fcar (x);
+      x = Fcdr (x);
+      file_name_data = Fcdr (cell);
+      if (!NILP (file_name_data) && STRINGP (Fcar (file_name_data))
+         && Fstring_equal (Fcar (file_name_data), file_name)
+         && NUMBERP (Fcar (cell)))
+        {
+          int const magicno = XINT (Fcar (cell));
+          watch_list = Fdelete (cell, watch_list);
+          if (inotify_rm_watch (inotifyfd, magicno) == -1)
+            report_file_error ("Could not unwatch file",
+                               Fcons (file_name, Qnil));
+
+          /* Cleanup if watch_list is empty.  */
+          if (NILP (watch_list))
+            {
+              close (inotifyfd);
+              delete_read_fd (inotifyfd);
+              inotifyfd = uninitialized;
+            }
+          return Qt;
+        }
+    }
+  return Qnil;
+}
+
+#else /* HAVE_INOTIFY */
+#error "Filewatch defined but no watch mechanism (inotify) available"
+#endif /* HAVE_INOTIFY */
+
+void
+syms_of_filewatch (void)
+{
+  DEFSYM (Qmodify, "modify");
+  DEFSYM (Qmove, "move");
+  DEFSYM (Qattrib, "attrib");
+  DEFSYM (Qdelete, "delete");
+  DEFSYM (Qfrom, "from");
+  DEFSYM (Qto, "to");
+
+  DEFSYM (Qunkown_aspect, "unkown-aspect");
+
+  defsubr (&Sfile_watch);
+  defsubr (&Sfile_unwatch);
+}
+
+#endif /* HAVE_FILEWATCH */
diff --git a/src/keyboard.c b/src/keyboard.c
index 7bc406a..ccf25f7 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -329,6 +329,9 @@ static Lisp_Object Qsave_session;
 #ifdef HAVE_DBUS
 static Lisp_Object Qdbus_event;
 #endif
+#ifdef HAVE_FILEWATCH
+static Lisp_Object Qfilewatch_event;
+#endif /* HAVE_FILEWATCH */
 static Lisp_Object Qconfig_changed_event;
 
 /* Lisp_Object Qmouse_movement; - also an event header */
@@ -4017,6 +4020,13 @@ kbd_buffer_get_event (KBOARD **kbp,
 	  kbd_fetch_ptr = event + 1;
 	}
 #endif
+#ifdef HAVE_FILEWATCH
+      else if (event->kind == FILEWATCH_EVENT)
+        {
+          obj = make_lispy_event (event);
+          kbd_fetch_ptr = event + 1;
+        }
+#endif
       else if (event->kind == CONFIG_CHANGED_EVENT)
 	{
 	  obj = make_lispy_event (event);
@@ -5913,6 +5923,13 @@ make_lispy_event (struct input_event *event)
       }
 #endif /* HAVE_DBUS */
 
+#ifdef HAVE_FILEWATCH
+    case FILEWATCH_EVENT:
+      {
+        return Fcons (Qfilewatch_event, event->arg);
+      }
+#endif /* HAVE_FILEWATCH */
+
     case CONFIG_CHANGED_EVENT:
 	return Fcons (Qconfig_changed_event,
                       Fcons (event->arg,
@@ -11524,6 +11541,10 @@ syms_of_keyboard (void)
   DEFSYM (Qdbus_event, "dbus-event");
 #endif
 
+#ifdef HAVE_FILEWATCH
+  DEFSYM (Qfilewatch_event, "filewatch-event");
+#endif /* HAVE_FILEWATCH */
+
   DEFSYM (QCenable, ":enable");
   DEFSYM (QCvisible, ":visible");
   DEFSYM (QChelp, ":help");
@@ -12274,6 +12295,13 @@ keys_of_keyboard (void)
 			    "dbus-handle-event");
 #endif
 
+#ifdef HAVE_FILEWATCH
+  /* Define a special event which is raised for filewatch callback
+     functions.  */
+  initial_define_lispy_key (Vspecial_event_map, "filewatch-event",
+                            "filewatch-handle-event");
+#endif /* HAVE_FILEWATCH */
+
   initial_define_lispy_key (Vspecial_event_map, "config-changed-event",
 			    "ignore");
 }
diff --git a/src/lisp.h b/src/lisp.h
index 8a504e8..8b21e0e 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3430,6 +3430,11 @@ EXFUN (Fxw_display_color_p, 1);
 EXFUN (Fx_focus_frame, 1);
 #endif
 
+/* Defined in filewatch.c */
+#ifdef HAVE_FILEWATCH
+extern void syms_of_filewatch (void);
+#endif
+
 /* Defined in xfaces.c */
 extern Lisp_Object Qdefault, Qtool_bar, Qfringe;
 extern Lisp_Object Qheader_line, Qscroll_bar, Qcursor;
diff --git a/src/termhooks.h b/src/termhooks.h
index 6a58517..9db2019 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -206,6 +206,11 @@ enum event_kind
   , NS_NONKEY_EVENT
 #endif
 
+#ifdef HAVE_FILEWATCH
+  /* File or directory was changed.  */
+  , FILEWATCH_EVENT
+#endif
+
 };
 
 /* If a struct input_event has a kind which is SELECTION_REQUEST_EVENT
-- 
1.7.5.2