Re: [PATCH] tar: fix verbose output with extract-to-stdout

Applied in modified form (making "tar xvO" follow GNU tar behavior).
Thank you.

On Thu, Jul 30, 2026 at 8:03 PM ThorstenB via busybox
<[email protected]> wrote:
>
> Combining the verbose (-v) and extract-to-stdout (-O) options caused
> verbose output and extracted file data to be interleaved unpredictably on
> stdout. Verbose listing uses buffered stdio (printf()/puts()), while file
> contents are written directly to the stdout file descriptor.
>
> GNU tar also combines buffered verbose output with unbuffered writes for
> "-vO", however, GNU tar writes verbose output to stderr, so the two streams
> remain separate and consistent. BusyBox tar writes both to stdout, making
> the interaction between buffered and unbuffered output visible.
>
> Patch only affects the extract-to-stdout ("-O") path, and only when
> combined with verbose output. It flushes stdout before writing file
> contents so that, for each archive member, verbose output is emitted
> before the corresponding file data.
>
> Includes two test cases.
>
> function                                             old     new   delta
> data_extract_to_stdout                                19      36     +17
> ------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 1/0 up/down: 17/0)               Total: 17 bytes
>
> Signed-off-by: ThorstenB <[email protected]>
> ---
>  archival/libarchive/data_extract_to_stdout.c   |  3 +++
>  .../tar/tar-verbose-extract-to-standard-output | 18 ++++++++++++++++++
>  ...tar-very-verbose-extract-to-standard-output | 18 ++++++++++++++++++
>  3 files changed, 39 insertions(+)
>  create mode 100644 testsuite/tar/tar-verbose-extract-to-standard-output
>  create mode 100644 testsuite/tar/tar-very-verbose-extract-to-standard-output
>
> diff --git a/archival/libarchive/data_extract_to_stdout.c b/archival/libarchive/data_extract_to_stdout.c
> index 520041329..167a15e7c 100644
> --- a/archival/libarchive/data_extract_to_stdout.c
> +++ b/archival/libarchive/data_extract_to_stdout.c
> @@ -7,6 +7,9 @@
>
>  void FAST_FUNC data_extract_to_stdout(archive_handle_t *archive_handle)
>  {
> +       // flush buffered stdout before writing directly to STDOUT_FILENO
> +       fflush(stdout);
> +
>         bb_copyfd_exact_size(archive_handle->src_fd,
>                         STDOUT_FILENO,
>                         archive_handle->file_header->size);
> diff --git a/testsuite/tar/tar-verbose-extract-to-standard-output b/testsuite/tar/tar-verbose-extract-to-standard-output
> new file mode 100644
> index 000000000..702dac92e
> --- /dev/null
> +++ b/testsuite/tar/tar-verbose-extract-to-standard-output
> @@ -0,0 +1,18 @@
> +# FEATURE: CONFIG_FEATURE_TAR_CREATE
> +echo "data 1" > file1.txt
> +echo "data 2" > file2.txt
> +echo "data 3" > file3.txt
> +
> +busybox tar cf test.tar file1.txt file2.txt file3.txt
> +busybox tar xvOf test.tar > output.txt
> +
> +cat > expected.txt << 'EOF'
> +file1.txt
> +data 1
> +file2.txt
> +data 2
> +file3.txt
> +data 3
> +EOF
> +
> +cmp expected.txt output.txt
> diff --git a/testsuite/tar/tar-very-verbose-extract-to-standard-output b/testsuite/tar/tar-very-verbose-extract-to-standard-output
> new file mode 100644
> index 000000000..b743d3994
> --- /dev/null
> +++ b/testsuite/tar/tar-very-verbose-extract-to-standard-output
> @@ -0,0 +1,18 @@
> +# FEATURE: CONFIG_FEATURE_TAR_CREATE
> +echo "data 1" > file1.txt
> +echo "data 2" > file2.txt
> +echo "data 3" > file3.txt
> +
> +busybox tar cf test.tar file1.txt file2.txt file3.txt
> +busybox tar xvvOf test.tar > output.txt
> +
> +# create expected output
> +busybox tar tvvf test.tar file1.txt > expected.txt
> +cat file1.txt >> expected.txt
> +busybox tar tvvf test.tar file2.txt >> expected.txt
> +cat file2.txt >> expected.txt
> +busybox tar tvvf test.tar file3.txt >> expected.txt
> +cat file3.txt >> expected.txt
> +
> +cmp expected.txt output.txt
> +
> --
> 2.51.0
>
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