[PATCH v3 3/4] qga: Add optional `merge-output` flag to guest-exec qapi

[Daniel Xu]

Currently, the 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 optional flag to the guest-exec 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       | 28 ++++++++++++++++++++++++++--
 qga/qapi-schema.json |  6 +++++-
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/qga/commands.c b/qga/commands.c
index 172826f8f8..cfce13d034 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;
 
@@ -384,6 +398,7 @@ GuestExec *qmp_guest_exec(const char *path,
                        bool has_env, strList *env,
                        const char *input_data,
                        bool has_capture_output, bool capture_output,
+                       bool has_merge_output, bool merge_output,
                        Error **errp)
 {
     GPid pid;
@@ -397,6 +412,7 @@ GuestExec *qmp_guest_exec(const char *path,
     GIOChannel *in_ch, *out_ch, *err_ch;
     GSpawnFlags flags;
     bool has_output = (has_capture_output && capture_output);
+    bool has_merge = (has_merge_output && merge_output);
     g_autofree uint8_t *input = NULL;
     size_t ninput = 0;
 
@@ -410,6 +426,14 @@ GuestExec *qmp_guest_exec(const char *path,
         }
     }
 
+#if defined(G_OS_WIN32)
+    /* FIXME: see comment in guest_exec_task_setup() */
+    if (has_merge) {
+        error_setg(errp, "merge-output unsupported on windows");
+        return NULL;
+    }
+#endif
+
     argv = guest_exec_get_args(&arglist, true);
     envp = has_env ? guest_exec_get_args(env, false) : NULL;
 
@@ -420,7 +444,7 @@ GuestExec *qmp_guest_exec(const char *path,
     }
 
     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 796434ed34..9c2367acdf 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -1211,6 +1211,9 @@
 # @input-data: data to be passed to process stdin (base64 encoded)
 # @capture-output: bool flag to enable capture of
 #                  stdout/stderr of running process. defaults to false.
+# @merge-output: bool flag to merge stdout/stderr of running process
+#                into stdout. only effective if used with @capture-output.
+#                not effective on windows guests. defaults to false. (since 
8.0)
 #
 # Returns: PID on success.
 #
@@ -1218,7 +1221,8 @@
 ##
 { 'command': 'guest-exec',
   'data':    { 'path': 'str', '*arg': ['str'], '*env': ['str'],
-               '*input-data': 'str', '*capture-output': 'bool' },
+               '*input-data': 'str', '*capture-output': 'bool',
+               '*merge-output': 'bool' },
   'returns': 'GuestExec' }
 
 
-- 
2.39.1