[Libguestfs] [PATCH v2 3/4] common/mltools: allow fd for machine readable output

[Richard W.M. Jones]

On Thu, Mar 28, 2019 at 05:59:30PM +0100, Pino Toscano wrote:
> Allow to specify a file descriptor for the machine readable output.
> 
> Use the same assumption as done in v2v, i.e. that Unix.file_descr is
> simply the int file descriptor.
> ---
>  common/mltools/test-machine-readable.sh |  7 +++++++
>  common/mltools/tools_utils.ml           | 11 ++++++++++-
>  lib/guestfs.pod                         |  5 +++++
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/common/mltools/test-machine-readable.sh b/common/mltools/test-machine-readable.sh
> index 1162c58e9..824460e6d 100755
> --- a/common/mltools/test-machine-readable.sh
> +++ b/common/mltools/test-machine-readable.sh
> @@ -65,3 +65,10 @@ test $($t --machine-readable=stream:stdout |& wc -l) -eq 3
>  # Output "stream:stderr".
>  $t --machine-readable=stream:stderr 2>&1 >/dev/null | grep 'machine-readable'
>  test $($t --machine-readable=stream:stderr 2>&1 >/dev/null | wc -l) -eq 2
> +
> +# Output "fd:".
> +fn="$tmpdir/fdfile"
> +exec 4>"$fn"
> +$t --machine-readable=fd:4
> +exec 4>&-
> +test $(cat "$fn" | wc -l) -eq 1
> diff --git a/common/mltools/tools_utils.ml b/common/mltools/tools_utils.ml
> index ade4cb37f..35478f39e 100644
> --- a/common/mltools/tools_utils.ml
> +++ b/common/mltools/tools_utils.ml
> @@ -41,6 +41,7 @@ type machine_readable_output_type =
>    | NoOutput
>    | Channel of out_channel
>    | File of string
> +  | Fd of int
>  let machine_readable_output = ref NoOutput
>  let machine_readable_channel = ref None
>  let machine_readable () =
> @@ -50,7 +51,10 @@ let machine_readable () =
>          match !machine_readable_output with
>          | NoOutput -> None
>          | Channel chan -> Some chan
> -        | File f -> Some (open_out f) in
> +        | File f -> Some (open_out f)
> +        | Fd fd ->
> +          (* Note that Unix.file_descr is really just an int. *)
> +          Some (Unix.out_channel_of_descr (Obj.magic fd)) in
>        machine_readable_channel := chan
>      );
>      !machine_readable_channel
> @@ -296,6 +300,11 @@ let create_standard_options argspec ?anon_fun ?(key_opts = false) ?(machine_read
>            | n ->
>              error (f_"invalid output stream for --machine-readable: %s") fmt in
>          machine_readable_output := Channel chan
> +      | "fd" ->
> +        (try
> +          machine_readable_output := Fd (int_of_string outname)
> +        with Failure _ ->
> +          error (f_"invalid output fd for --machine-readable: %s") fmt)
>        | n ->
>          error (f_"invalid output for --machine-readable: %s") fmt
>        )
> diff --git a/lib/guestfs.pod b/lib/guestfs.pod
> index 53cece2da..f11028466 100644
> --- a/lib/guestfs.pod
> +++ b/lib/guestfs.pod
> @@ -3287,6 +3287,11 @@ The possible values are:
>  
>  =over 4
>  
> +=item B<fd:>I<fd>
> +
> +The output goes to the specified I<fd>, which is a file descriptor
> +already opened for writing.
> +
>  =item B<file:>F<filename>
>  
>  The output goes to the specified F<filename>.

Much simpler :-)

ACK

Rich.

-- 
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