Enhance nscd's inotify support (Bug 14906).

In bug 14906 the user complains that the inotify support in nscd
is not sufficient when it comes to detecting changes in the
configurationfiles that should be watched for the various databases.

The current nscd implementation uses inotify to watch for changes in
the configuration files, but adds watches only for IN_DELETE_SELF and
IN_MODIFY. These watches are insufficient to cover even the most basic
uses by a system administrator. For example using emacs or vim to edit
a configuration file should trigger a reload but it might not if
the editors use move to atomically update the file. This atomic update
changes the inode and thus removes the notification on the file (as
inotify is based on inodes). Thus the inotify support in nscd for
configuration files is insufficient to account for the average use
cases of system administrators and users.

The inotify support is significantly enhanced and described here:
https://www.sourceware.org/ml/libc-alpha/2015-02/msg00504.html

Tested on x86_64 with and without inotify support.

1 files changed, 56 insertions, 4 deletions

diff --git a/nscd/nscd.h b/nscd/nscd.h
index 17a0a96278..75c2eccea0 100644
--- a/nscd/nscd.h
+++ b/nscd/nscd.h
@@ -61,17 +61,67 @@ typedef enum
    80% of the thread stack size.  */
 #define MAX_STACK_USE ((8 * NSCD_THREAD_STACKSIZE) / 10)
 
-
-/* Registered filename used to fill database.  */
+/* Records the file registered per database that when changed
+   or modified requires invalidating the database.  */
 struct traced_file
 {
+  /* Tracks the last modified time of the traced file.  */
   time_t mtime;
+  /* Support multiple registered files per database.  */
   struct traced_file *next;
   int call_res_init;
-  int inotify_descr;
+  /* Requires Inotify support to do anything useful.  */
+#define TRACED_FILE	0
+#define TRACED_DIR	1
+  int inotify_descr[2];
+# ifndef PATH_MAX
+#  define PATH_MAX 1024
+# endif
+  /* The parent directory is used to scan for creation/deletion.  */
+  char dname[PATH_MAX];
+  /* Just the name of the file with no directory component.  */
+  char *sfname;
+  /* The full-path name of the registered file.  */
   char fname[];
 };
 
+/* Initialize a `struct traced_file`.  As input we need the name
+   of the file, and if invalidation requires calling res_init.
+   If CRINIT is 1 then res_init will be called after invalidation
+   or if the traced file is changed in any way, otherwise it will
+   not.  */
+static inline void
+init_traced_file(struct traced_file *file, const char *fname, int crinit)
+{
+   char *dname;
+   file->mtime = 0;
+   file->inotify_descr[TRACED_FILE] = -1;
+   file->inotify_descr[TRACED_DIR] = -1;
+   strcpy (file->fname, fname);
+   /* Compute the parent directory name and store a copy.  The copy makes
+      it much faster to add/remove watches while nscd is running instead
+      of computing this over and over again in a temp buffer.  */
+   file->dname[0] = '\0';
+   dname = strrchr (fname, '/');
+   if (dname != NULL)
+     {
+       size_t len = (size_t)(dname - fname);
+       if (len > sizeof (file->dname))
+	 abort ();
+       strncpy (file->dname, file->fname, len);
+       file->dname[len] = '\0';
+     }
+   /* The basename is the name just after the last forward slash.  */
+   file->sfname = &dname[1];
+   file->call_res_init = crinit;
+}
+
+#define define_traced_file(id, filename) 			\
+static union							\
+{								\
+  struct traced_file file;					\
+  char buf[sizeof (struct traced_file) + sizeof (filename)];	\
+} id##_traced_file;
 
 /* Structure describing dynamic part of one database.  */
 struct database_dyn
@@ -90,7 +140,6 @@ struct database_dyn
   int propagate;
   struct traced_file *traced_files;
   const char *db_filename;
-  time_t file_mtime;
   size_t suggested_module;
   size_t max_db_size;
 
@@ -211,6 +260,9 @@ void do_exit (int child_ret, int errnum, const char *format, ...);
 /* connections.c */
 extern void nscd_init (void);
 extern void register_traced_file (size_t dbidx, struct traced_file *finfo);
+#ifdef HAVE_INOTIFY
+extern void install_watches (struct traced_file *finfo);
+#endif
 extern void close_sockets (void);
 extern void start_threads (void) __attribute__ ((__noreturn__));