Re: [PATCH 2/3] t6500: get hostname from "git var"

[Junio C Hamano <gitster@pobox.com>]

Isabella Caselli <bellacaselli20@gmail.com> writes:

> The test "background auto gc respects lock for all operations" simulates
> a concurrent gc by writing our shell's pid and hostname to "gc.pid".
> It gets the hostname from the "hostname" command, falling back to
> "unknown" if the command fails.
>
> "git gc" gets its hostname from the system and only checks whether the
> pid is alive if the two hostnames match. Otherwise, it assumes the
> lock belongs to a gc running on another machine. Since the test passes
> in either case, a missing "hostname" command or a mismatch between
> its output and the system hostname can cause the test to silently
> exercise the wrong case.

"exercise the wrong case", meaning...  where hostname(1) output is
different from "git var GIT_HOSTNAME" (aka xgethostname()), we would
have written bogus name in .git/gc.pid file, simulating the case where
gc.pid was written by a process running on a different machine.

What is the implications of doing so?
>
> Use "git var GIT_HOSTNAME" to get the same hostname as "git gc".
> Keep the "unknown" fallback, which is also used by "git gc" when it
> cannot determine the hostname.
>
> Helped-by: Jeff King <peff@peff.net>
> Signed-off-by: Isabella Caselli <bellacaselli20@gmail.com>
> ---
>  t/t6500-gc.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
> index a7142ab815..f928089bf0 100755
> --- a/t/t6500-gc.sh
> +++ b/t/t6500-gc.sh
> @@ -413,7 +413,7 @@ test_expect_success 'background auto gc respects lock for all operations' '
>  
>  	# now fake a concurrent gc that holds the lock; we can use our
>  	# shell pid so that it looks valid.
> -	hostname=$(hostname || echo unknown) &&
> +	hostname=$(git var GIT_HOSTNAME || echo unknown) &&
>  	shell_pid=$$ &&
>  	if test_have_prereq MINGW && test -f /proc/$shell_pid/winpid
>  	then