Re: [PATCH] tail: display file headers correctly with inotify

[Bernhard Voelker]

Nice one, but I think the fix is not sufficient ... see below.

On 06/09/2015 02:54 AM, Pádraig Brady wrote:
> diff --git a/src/tail.c b/src/tail.c
> index c9736ca..047d93c 100644
> --- a/src/tail.c
> +++ b/src/tail.c
> @@ -1046,7 +1046,9 @@ recheck (struct File_spec *f, bool blocking)
>          {
>            /* This happens when one iteration finds the file missing,
>               then the preceding <dev,inode> pair is reused as the
> -             file is recreated.  */
> +             file is recreated.  XXX: This means the file is redisplayed
> +             in --follow=name mode if renamed away from and back to
> +             a monitored name.  */
>            new_file = true;
>          }
>        else

s/XXX: // ?

> diff --git a/tests/tail-2/F-headers.sh b/tests/tail-2/F-headers.sh
> new file mode 100755
> index 0000000..9355c0c
> --- /dev/null
> +++ b/tests/tail-2/F-headers.sh
> @@ -0,0 +1,59 @@
> +#!/bin/sh
> +# Ensure tail -F distinguishes output with the correct headers
> +# Between coreutils 7.5 and 8.23 inclusive, 'tail -F ...' would
> +# not output headers for cor created/renamed files in certain cases.

s/ cor / /

> +for mode in '' '---disable-inotify'; do
> +  rm -f a b out
> +
> +  tail $mode -F $fastpoll a b > out 2>&1 & pid=$!
> +
> +  # Wait up to 12.7s for tail to start.
> +  tail_re="cannot open 'b'" retry_delay_ check_tail_output .1 7 ||
> +    { cat out; fail=1; }
> +
> +  echo x > a
> +  # Wait up to 12.7s for a's header to appear in the output:
> +  tail_re='==> a <==' retry_delay_ check_tail_output .1 7 ||
> +    { echo "$0: a: unexpected delay?"; cat out; fail=1; }
> +
> +  echo y > b
> +  # Wait up to 12.7s for a's header to appear in the output:
> +  tail_re='==> b <==' retry_delay_ check_tail_output .1 7 ||
> +    { echo "$0: a: unexpected delay?"; cat out; fail=1; }

s/ a: / b: /

While this patch fixes the outputting of the header for multiple
files, it does not fix the same issue for the same file, i.e. the
"==> file <==" header is missing when a file re-appears the 2nd
time.  Reproducer:

  rm -f a b out
  src/tail -F a b > out 2>&1 &

  sleep 2; echo a > a

  sleep 2; rm a

  sleep 2; echo a > a

  sleep 2; kill $!

Output:

  src/tail: cannot open ‘a’ for reading: No such file or directory
  src/tail: cannot open ‘b’ for reading: No such file or directory
  src/tail: ‘a’ has appeared;  following new file
  ==> a <==
  a
  src/tail: ‘a’ has been replaced;  following new file
  a

Shouldn't tail(1) output the "==> a <==" header before the last
line here, too?

Thanks & have a nice day,
Berny