[PATCH] dd: Error out when unable to write entire read block

[Denys Vlasenko]

Fixed, thanks!

On Wed, Jan 10, 2018 at 12:08 AM, Ari Sundholm <ari at tuxera.com> wrote:
> Busybox dd has a difference in behavior compared to coreutils dd
> in the case where the block count has been given and the last block
> can only partially be written (usually due to ENOSPC):
>
>         $ dd if=/dev/zero of=foo bs=100M count=8; echo $?; rm foo
>         dd: error writing 'foo': No space left on device
>         8+0 records in
>         7+0 records out
>         805220352 bytes (805 MB, 768 MiB) copied, 0.405782 s, 2.0 GB/s
>         1
>         $ busybox dd if=/dev/zero of=foo bs=100M count=8; echo $?; rm foo
>         8+0 records in
>         7+1 records out
>         0
>         $ df -h .
>         Filesystem      Size  Used Avail Use% Mounted on
>         tmpfs           768M  8.0K  768M   1% [redacted]
>         $
>
> This breaks scripts which rely on busybox dd giving an exit value
> indicating failure when writing data fails.
>
> The solution is to error out when the block that was just read (be
> it full or partial) couldn't be written out in full, just as coreutils
> dd does.
>
> Signed-off-by: Ari Sundholm <ari at tuxera.com>
> ---
>  coreutils/dd.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/coreutils/dd.c b/coreutils/dd.c
> index d302f35..0bce80c 100644
> --- a/coreutils/dd.c
> +++ b/coreutils/dd.c
> @@ -195,13 +195,15 @@ static bool write_and_stats(const void *buf, size_t len, size_t obs,
>         ssize_t n = full_write_or_warn(buf, len, filename);
>         if (n < 0)
>                 return 1;
> -       if ((size_t)n == obs)
> -               G.out_full++;
> -       else if (n) /* > 0 */
> -               G.out_part++;
>  #if ENABLE_FEATURE_DD_THIRD_STATUS_LINE
>         G.total_bytes += n;
>  #endif
> +       if ((size_t)n == obs)
> +               G.out_full++;
> +       else if ((size_t)n == len)
> +               G.out_part++;
> +       else /* if ((size_t)n != len) */
> +                       return 1;
>         return 0;
>  }
>
> --
> 2.7.4
>
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