Re: [PATCH] df: Fix bug when totaling unknown values.

[Jim Meyering]

Paul Eggert wrote:
> This fixes a bug reported by "make check" on a Solaris 10 host with
> some funky file systems.
>
> * src/df.c (show_dev): Don't add UINTMAX_MAX to grand totals, as that
> value indicates that the true value is unknown; adding it effectively
> subtracts 1 from the total, whereas we want to leave the total alone.
> ---
>  src/df.c |   19 ++++++++++++-------
>  1 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/src/df.c b/src/df.c
> index 0bb3b1e..bb24934 100644
> --- a/src/df.c
> +++ b/src/df.c
> @@ -393,8 +393,10 @@ show_dev (char const *disk, char const *mount_point,
>        negate_available = false;
>        available_to_root = available;
>
> -      grand_fsu.fsu_files += total;
> -      grand_fsu.fsu_ffree += available;

Good timing.
Matthew Woehlke recently reported failure of the df/total-verify test.
Looking into it, we found that one of those values was UINTMAX_MAX - 1.
So how about a function like summable (uintmax_t val) to be used
in place of each of those 5 tests?

> +      if (total != UINTMAX_MAX)
> +     grand_fsu.fsu_files += total;
> +      if (available != UINTMAX_MAX)
> +     grand_fsu.fsu_ffree += available;
>      }
>    else
>      {
> @@ -422,11 +424,14 @@ show_dev (char const *disk, char const *mount_point,
>                         & (available != UINTMAX_MAX));
>        available_to_root = fsu.fsu_bfree;
>
> -      grand_fsu.fsu_blocks += input_units * total;
> -      grand_fsu.fsu_bfree  += input_units * available_to_root;
> -      add_uint_with_neg_flag (&grand_fsu.fsu_bavail,
> -                           &grand_fsu.fsu_bavail_top_bit_set,
> -                           input_units * available, negate_available);
> +      if (total != UINTMAX_MAX)
> +     grand_fsu.fsu_blocks += input_units * total;
> +      if (available_to_root != UINTMAX_MAX)
> +     grand_fsu.fsu_bfree  += input_units * available_to_root;
> +      if (available != UINTMAX_MAX)
> +     add_uint_with_neg_flag (&grand_fsu.fsu_bavail,
> +                             &grand_fsu.fsu_bavail_top_bit_set,
> +                             input_units * available, negate_available);
>      }
>
>    used = UINTMAX_MAX;