Re: [PATCH v5 2/3] qga: Add `merged` variant to GuestExecCaptureOutputMode

[Daniel P . Berrangé]

On Thu, Mar 09, 2023 at 03:40:57PM -0700, Daniel Xu wrote:
> Currently, any captured output (via `capture-output`) is segregated into
> separate GuestExecStatus fields (`out-data` and `err-data`). This means
> that downstream consumers have no way to reassemble the captured data
> back into the original stream.
> 
> This is relevant for chatty and semi-interactive (ie. read only) CLI
> tools.  Such tools may deliberately interleave stdout and stderr for
> visual effect. If segregated, the output becomes harder to visually
> understand.
> 
> This commit adds a new enum variant to the GuestExecCaptureOutputMode
> qapi to merge the output streams such that consumers can have a pristine
> view of the original command output.
> 
> Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
> ---
>  qga/commands.c       | 31 +++++++++++++++++++++++++++++--
>  qga/qapi-schema.json |  4 +++-
>  2 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/qga/commands.c b/qga/commands.c
> index 01f68b45ab..c347d434ed 100644
> --- a/qga/commands.c
> +++ b/qga/commands.c
> @@ -270,12 +270,26 @@ static void guest_exec_child_watch(GPid pid, gint 
> status, gpointer data)
>      g_spawn_close_pid(pid);
>  }
>  
> -/** Reset ignored signals back to default. */
>  static void guest_exec_task_setup(gpointer data)
>  {
>  #if !defined(G_OS_WIN32)
> +    bool has_merge = *(bool *)data;
>      struct sigaction sigact;
>  
> +    if (has_merge) {
> +        /*
> +         * FIXME: When `GLIB_VERSION_MIN_REQUIRED` is bumped to 2.58+, use
> +         * g_spawn_async_with_fds() to be portable on windows. The current
> +         * logic does not work on windows b/c `GSpawnChildSetupFunc` is run
> +         * inside the parent, not the child.
> +         */
> +        if (dup2(STDOUT_FILENO, STDERR_FILENO) != 0) {
> +            slog("dup2() failed to merge stderr into stdout: %s",
> +                 strerror(errno));
> +        }
> +    }
> +
> +    /* Reset ignored signals back to default. */
>      memset(&sigact, 0, sizeof(struct sigaction));
>      sigact.sa_handler = SIG_DFL;
>  
> @@ -409,6 +423,7 @@ GuestExec *qmp_guest_exec(const char *path,
>      GIOChannel *in_ch, *out_ch, *err_ch;
>      GSpawnFlags flags;
>      bool has_output = false;
> +    bool has_merge = false;

Wrap in  #ifndef _WIN32

>      GuestExecCaptureOutputMode output_mode;
>      g_autofree uint8_t *input = NULL;
>      size_t ninput = 0;
> @@ -445,13 +460,25 @@ GuestExec *qmp_guest_exec(const char *path,
>      case GUEST_EXEC_CAPTURE_OUTPUT_MODE_SEPARATED:
>          has_output = true;
>          break;
> +    case GUEST_EXEC_CAPTURE_OUTPUT_MODE_MERGED:
> +        has_output = true;
> +        has_merge = true;
> +        break;

Wrap in  #ifndef _WIN32

>      case GUEST_EXEC_CAPTURE_OUTPUT_MODE__MAX:
>          /* Silence warning; impossible branch */
>          break;
>      }
>  
> +#if defined(G_OS_WIN32)
> +    /* FIXME: see comment in guest_exec_task_setup() */
> +    if (has_merge) {
> +        error_setg(errp, "merged unsupported on windows");
> +        return NULL;
> +    }
> +#endif

THis can be dropped, since 'has_merge' won't exist for
Win32 builds.

> +
>      ret = g_spawn_async_with_pipes(NULL, argv, envp, flags,
> -            guest_exec_task_setup, NULL, &pid, input_data ? &in_fd : NULL,
> +            guest_exec_task_setup, &has_merge, &pid, input_data ? &in_fd : 
> NULL,
>              has_output ? &out_fd : NULL, has_output ? &err_fd : NULL, &gerr);
>      if (!ret) {
>          error_setg(errp, QERR_QGA_COMMAND_FAILED, gerr->message);
> diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
> index d1e00a4234..b4782525ae 100644
> --- a/qga/qapi-schema.json
> +++ b/qga/qapi-schema.json
> @@ -1210,11 +1210,13 @@
>  # @stderr: only capture stderr
>  # @separated: capture both stdout and stderr, but separated into
>  #             GuestExecStatus out-data and err-data, respectively
> +# @merged: capture both stdout and stderr, but merge together
> +#          into out-data. not effective on windows guests.
>  #
>  # Since: 8.0
>  ##
>   { 'enum': 'GuestExecCaptureOutputMode',
> -   'data': [ 'none', 'stdout', 'stderr', 'separated' ] }
> +   'data': [ 'none', 'stdout', 'stderr', 'separated', 'merged' ] }

Actually, I've just realized we can make this conditional:


 'data': [ 'none', 'stdout', 'stderr', 'separated',
           { 'name': 'merged', 'if': 'CONFIG_WIN32' } ] }

so the constant doesn't even exist in Win32 builds.

With regards,
Daniel
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