truncate: improve handling of non regular files

Previously we copied `dd` and suppressed error messages
when truncating neither regular files or shared mem objects.
This was valid for `dd`, as truncation is ancillary to copying
it may also do, but for `truncate` we should display all errors.
Also we used the st_size from non regular files which is undefined,
so we display an error when the user tries this.

* src/truncate (do_truncate):  Error when referencing the size
of non regular files or non shared memory objects.  Display all
errors returned by ftruncate().
(main): Error when referencing the size of non regular files or
non shared memory objects.  Don't suppress error messages for
any file types that can't be opened for writing.
* tests/misc/truncate-dir-fail: Check that referencing the
size of a directory is not supported.
* tests/misc/truncate-fifo: Ensure the test doesn't hang
by using the `timeout` command.  Don't test the return from
running ftruncate on the fifo as it's system dependent as
to whether this fails or not.
NEWS: Mention the change in behavior.
Reported by Jim Meyering.

1 files changed, 4 insertions, 4 deletions

diff --git a/tests/misc/truncate-fifo b/tests/misc/truncate-fifo
index 8e2276dab..a4c36cb90 100755
--- a/tests/misc/truncate-fifo
+++ b/tests/misc/truncate-fifo
@@ -1,5 +1,5 @@
 #!/bin/sh
-# Make sure truncate works on fifos without hanging or errors
+# Make sure truncate works on fifos without hanging
 
 # Copyright (C) 2008-2010 Free Software Foundation, Inc.
 
@@ -23,9 +23,9 @@ fi
 
 . $srcdir/test-lib.sh
 
-mkfifo_or_skip_ "fifo"
+mkfifo_or_skip_ fifo
 
-
-truncate -s0 "fifo" || fail=1
+timeout 10 truncate -s0 fifo
+test "$?" = 124 && fail=1
 
 Exit $fail