Re: [PATCH v2 3/3] core: convert build-time USE_NSEC into runtime core.useNanosec

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

"D. Ben Knoble" <ben.knoble@gmail.com> writes:

> -#ifdef USE_NSEC
> -	if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
> -		changed |= MTIME_CHANGED;
> -	if (cfg->trust_ctime && cfg->check_stat &&
> -	    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
> -		changed |= CTIME_CHANGED;
> -#endif
> +	if (cfg->use_nanosec) {
> +		if (cfg->check_stat && sd->sd_mtime.nsec != ST_MTIME_NSEC(*st))
> +			changed |= MTIME_CHANGED;
> +		if (cfg->trust_ctime && cfg->check_stat &&
> +		    sd->sd_ctime.nsec != ST_CTIME_NSEC(*st))
> +			changed |= CTIME_CHANGED;
> +	}
>  
>  	if (cfg->check_stat) {
>  		if (sd->sd_uid != (unsigned int) st->st_uid ||

This is iffy.

If you have core.usenanosec=true in a networked $HOME/.gitconfig
mounted on both USE_NSEC-capable and incapable platforms, what would
ST_CTIME_NSEC() yield on the latter?  I wonder if cfg's
'.use_nanosec' should be force-disabled in NO_NSEC builds, or
something similar?