doc: tail/inotify does use --sleep-interval=S, with --pid=P

* doc/coreutils.texi (tail invocation): Mention it.
* src/tail.c (usage): Likewise.
(tail_forever_inotify): Clarify comment.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/tail.c b/src/tail.c
index bcd2d9970..88fbd10b8 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -302,7 +302,8 @@ Mandatory arguments to long options are mandatory for short options too.\n\
      fputs (_("\
   -s, --sleep-interval=N   with -f, sleep for approximately N seconds\n\
                              (default 1.0) between iterations.\n\
-                             With inotify, this option is rarely useful.\n\
+                             With inotify and --pid=P, check process P at\n\
+                             least once every N seconds.\n\
   -v, --verbose            always output headers giving file names\n\
 "), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
@@ -1422,9 +1423,10 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files,
   evlen += sizeof (struct inotify_event) + 1;
   evbuf = xmalloc (evlen);
 
-  /* Wait for inotify events and handle them.  Events on directories make sure
-     that watched files can be re-added when -F is used.
-     This loop sleeps on the `safe_read' call until a new event is notified.  */
+  /* Wait for inotify events and handle them.  Events on directories
+     ensure that watched files can be re-added when following by name.
+     This loop blocks on the `safe_read' call until a new event is notified.
+     But when --pid=P is specified, tail usually waits via the select.  */
   while (1)
     {
       struct File_spec *fspec;