Subject: Re: [PATCH] tests: disable fsync everywhere

From: Junio C Hamano <[email-masked]>
Date: Thu, 28 Oct 2021 22:18:24 -0700

Eric Wong <[email-masked]> writes:

> @@ -42,6 +42,7 @@ const char *git_hooks_path;
>  int zlib_compression_level = Z_BEST_SPEED;
>  int pack_compression_level = Z_DEFAULT_COMPRESSION;
>  int fsync_object_files;
> +int use_fsync = -1;

OK, (-1) is "undetermined yet", as usual.

> diff --git a/git-cvsserver.perl b/git-cvsserver.perl
> index 64319bed43..4c8118010a 100755
> --- a/git-cvsserver.perl
> +++ b/git-cvsserver.perl
> @@ -3607,6 +3607,22 @@ package GITCVS::updater;
>  use strict;
>  use warnings;
>  use DBI;
> +our $_use_fsync;
> +
> +# n.b. consider using Git.pm
> +sub use_fsync {
> +    if (!defined($_use_fsync)) {
> +        my $x = $ENV{GIT_TEST_FSYNC};
> +        if (defined $x) {

I would have expected to see "exists $ENV{GIT_TEST_FSYNC}", but I
guess there is no way to place in %ENV anyway, so it would be OK.

> +            local $ENV{GIT_CONFIG};
> +            delete $ENV{GIT_CONFIG};

OK, "git -c test.fsync=no cvsserver" would added something to
GIT_CONFIG that would affect test.fsync, but wouldn't the usual
last-one-wins rule be sufficient to check the value of $x using the
next construction, no matter what is in GIT_CONFIG?  I do not think
it would hurt to delete $ENV{GIT_CONFIG}, but I am not sure how it
is necessary.

> +            my $v = ::safe_pipe_capture('git', '-c', "test.fsync=$x",
> +                                        qw(config --type=bool test.fsync));

THis is an interesting idiom.

> +            $_use_fsync = defined($v) ? ($v eq "true\n") : 1;
> +        }
> +    }
> +    $_use_fsync;
> +}

> +# TODO: move this to Git.pm?
> +sub use_fsync {

Possibly, but in a slightly more general form, taking the name of
the environment variable that holds a boolean value as an argument,
or something?

> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index a291a5d4a2..21f5fab999 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -489,6 +489,13 @@ then
>  	export GIT_PERL_FATAL_WARNINGS
>  fi
>  
> +case $GIT_TEST_FSYNC in
> +'')
> +	GIT_TEST_FSYNC=0
> +	export GIT_TEST_FSYNC
> +	;;
> +esac

> diff --git a/write-or-die.c b/write-or-die.c
> index 0b1ec8190b..a3d5784cec 100644
> --- a/write-or-die.c
> +++ b/write-or-die.c
> @@ -1,4 +1,5 @@
>  #include "cache.h"
> +#include "config.h"
>  #include "run-command.h"
>  
>  /*
> @@ -57,6 +58,10 @@ void fprintf_or_die(FILE *f, const char *fmt, ...)
>  
>  void fsync_or_die(int fd, const char *msg)
>  {
> +	if (use_fsync < 0)
> +		use_fsync = git_env_bool("GIT_TEST_FSYNC", 1);
> +	if (!use_fsync)
> +		return;

OK.  That's quite straight-forward.

>  	while (fsync(fd) < 0) {
>  		if (errno != EINTR)
>  			die_errno("fsync error on '%s'", msg);

Will queue.