tail: use inotify if it is available

* NEWS: Document the new feature.
* m4/jm-macros.m4: Check if inotify is present.
* src/tail.c (tail_forever_inotify): New function.
(main): Use the inotify-based function, if possible.
* tests/Makefile.am: Add new tests for tail.
* tests/test-lib.sh (require_proc_pid_status_, get_process_status_):
New functions.
* tests/tail-2/pid: New file.
* tests/tail-2/wait: New file.
* tests/tail-2/tail-n0f: Refactor code into the test-lib.sh
require_proc_pid_status_ function.

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/test-lib.sh b/tests/test-lib.sh
index e5eed8db6..d99e3a966 100644
--- a/tests/test-lib.sh
+++ b/tests/test-lib.sh
@@ -122,6 +122,11 @@ uid_is_privileged_()
   esac
 }
 
+get_process_status_()
+{
+  sed -n '/^State:[	 ]*\([[:alpha:]]\).*/s//\1/p' /proc/$1/status
+}
+
 # Convert an ls-style permission string, like drwxr----x and -rw-r-x-wx
 # to the equivalent chmod --mode (-m) argument, (=,u=rwx,g=r,o=x and
 # =,u=rw,g=rx,o=wx).  Ignore ACLs.
@@ -234,6 +239,17 @@ of group names or numbers.  E.g.,
   esac
 }
 
+# Is /proc/$PID/status supported?
+require_proc_pid_status_()
+{
+    sleep 2 &
+    local pid=$!
+    sleep .5
+    grep '^State:[	 ]*[S]' /proc/$pid/status > /dev/null 2>&1 ||
+    skip_test_ "/proc/$pid/status: missing or 'different'"
+    kill $pid
+}
+
 # Does the current (working-dir) file system support sparse files?
 require_sparse_support_()
 {