tail: with -f, use polling when a file is on an FS of unknown type

Before, we would use inotify in that case, which would work as long
as updates were taking place locally, but not at all when remote.
Move hard-coded list of known remote FS types into a more
maintainable table in stat.c, alongside the list of FS
names and magic numbers.  Generate a new is_local_fs_type function.
* src/Makefile.am (fs-is-local.h): New rule, generated file.
* src/extract-magic: Revamp to parse local/remote keyword after
each magic number in src/stat.c's case statements.
Accept new --local option.
* src/.gitignore: Ignore the generated fs-is-local.h.
* src/tail.c [HAVE_INOTIFY]: Include fs-is-local.h.
(fremote) [HAVE_INOTIFY]: Use the new function in place of
the switch stmt with hard-coded list of FS types.
Emit a warning when processing a file on a file system of unknown type.
* NEWS (Changes in behavior): Mention it.
Suggested by Sven Breuner.

1 files changed, 38 insertions, 10 deletions

diff --git a/src/extract-magic b/src/extract-magic
index 6bc054f50..57d3681ae 100644
--- a/src/extract-magic
+++ b/src/extract-magic
@@ -65,10 +65,15 @@ FIXME: describe
 
 OPTIONS:
 
-  Derive #define directives from specially formatted `case ...:' statements.
+  There are two modes of operation, the default, which is to emit
+  #define directives derived from specially formatted `case' statements,
+  and that with --local, which is to emit a static inline function
+  mapping S_MAGIC_* values to 1, 0, -1, corresponding to known-local,
+  known-remote/distributed/network and unknown, respectively.
 
-   --help             display this help and exit
-   --version          output version information and exit
+   --local    emit an is_local_fs_type function
+   --help     display this help and exit
+   --version  output version information and exit
 
 EOF
     }
@@ -76,8 +81,12 @@ EOF
 }
 
 {
+  # The default is to print S_MAGIC_* definitions.
+  my $emit_magic = 1;
+
   GetOptions
     (
+     local => sub { $emit_magic = 0 },
      help => sub { usage 0 },
      version => sub { print "$ME version $VERSION\n"; exit },
     ) or usage 1;
@@ -103,31 +112,50 @@ EOF
   # Fail if there is a `case S_MAGIC_.*' line without
   # a properly formed comment.
 
-  print <<EOF;
+  my $map_comment = <<EOF;
+/* Map each S_MAGIC_* value to 1, 0 or -1.
+   1 if it is known to be a remote file system type,
+   0 if it is known to be a local file system type, or -1 otherwise.  */
+EOF
+  my $magic_comment = <<EOF;
 /* Define the magic numbers as given by statfs(2).
    Please send additions to bug-coreutils\@gnu.org and meskes\@debian.org.
    This file is generated automatically from $file. */
-
-#if defined __linux__
 EOF
+  print $emit_magic ? $magic_comment : $map_comment;
+
+  $emit_magic
+    and print "\n#if defined __linux__\n";
+  $emit_magic
+    or print "static inline int\n"
+      . "is_local_fs_type (unsigned long int magic)\n"
+      . "{\n  switch (magic)\n    {\n";
 
   while (defined (my $line = <FH>))
     {
       $line =~ /^[ \t]+case S_MAGIC_/
         or next;
-      $line =~ m!^[ \t]+case (S_MAGIC_\w+): /\* (0x[0-9A-Fa-f]+) \*/$!
+      $line =~
+        m!^[ \t]+case (S_MAGIC_\w+): /\* (0x[0-9A-Fa-f]+) (local|remote) \*/!
         or (warn "$ME:$file:$.: malformed case S_MAGIC_... line"),
           $fail = 1, next;
       my $name = $1;
-      my $value = $2;
-      print "# define $name $value\n";
+      my $magic = $2;
+      my $local = $3 eq 'local' ? 1 : 0;
+      print $emit_magic
+        ? "# define $name $magic\n"
+        : "      case $name: return $local;\n";
     }
 
-  print <<\EOF;
+  $emit_magic
+    and print <<\EOF;
 #elif defined __GNU__
 # include <hurd/hurd_types.h>
 #endif
 EOF
+  $emit_magic
+    or printf "      default: return -1;\n    }\n}\n";
+
   close FH;
 
   exit $fail;