[PATCH 2/3] qga: Add optional stream-output argument to guest-exec

[Daniel Xu]

Currently, commands run through guest-exec are "silent" until they
finish running. This is fine for short lived commands. But for commands
that take a while, this is a bad user experience.

Usually long running programs know that they will run for a while. To
improve user experience, they will typically print some kind of status
to output at a regular interval. So that the user knows that their
command isn't just hanging.

This commit adds support for an optional stream-output parameter to
guest-exec. This causes subsequent calls to guest-exec-status to return
all buffered output. This allows downstream applications to be able to
relay "status" to the end user.

If stream-output is requested, it is up to the guest-exec-status caller
to keep track of the last seen output position and slice the returned
output appropriately. This is fairly trivial for a client to do. And it
is a more reliable design than having QGA internally keep track of
position -- for the cases that the caller "loses" a response.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 qga/commands.c       | 12 ++++++++++++
 qga/qapi-schema.json |  7 ++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/qga/commands.c b/qga/commands.c
index ce172edd2d..8cabc2460f 100644
--- a/qga/commands.c
+++ b/qga/commands.c
@@ -97,6 +97,7 @@ struct GuestExecInfo {
     int64_t pid_numeric;
     gint status;
     bool has_output;
+    bool stream_output;
     bool finished;
     GuestExecIOData in;
     GuestExecIOData out;
@@ -218,6 +219,15 @@ GuestExecStatus *qmp_guest_exec_status(int64_t pid, Error 
**errp)
 
         QTAILQ_REMOVE(&guest_exec_state.processes, gei, next);
         g_free(gei);
+    } else if (gei->stream_output) {
+        if (gei->out.length > 0) {
+            ges->out_data = g_base64_encode(gei->out.data, gei->out.length);
+            ges->has_out_truncated = gei->out.truncated;
+        }
+        if (gei->err.length > 0) {
+            ges->err_data = g_base64_encode(gei->err.data, gei->err.length);
+            ges->has_err_truncated = gei->err.truncated;
+        }
     }
 
     return ges;
@@ -410,6 +420,7 @@ GuestExec *qmp_guest_exec(const char *path,
                        bool has_env, strList *env,
                        const char *input_data,
                        GuestExecCaptureOutput *capture_output,
+                       bool has_stream_output, bool stream_output,
                        Error **errp)
 {
     GPid pid;
@@ -485,6 +496,7 @@ GuestExec *qmp_guest_exec(const char *path,
 
     gei = guest_exec_info_add(pid);
     gei->has_output = has_output;
+    gei->stream_output = has_stream_output && stream_output;
     g_child_watch_add(pid, guest_exec_child_watch, gei);
 
     if (input_data) {
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index b720dd4379..0a76e35082 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -1315,13 +1315,18 @@
 # @capture-output: bool flag to enable capture of stdout/stderr of
 #     running process.  defaults to false.
 #
+# @stream-output: causes future guest-exec-status calls to always
+#     return current captured output rather than waiting to return
+#     it all when the command exits. defaults to false. (since: 8.2)
+#
 # Returns: PID on success.
 #
 # Since: 2.5
 ##
 { 'command': 'guest-exec',
   'data':    { 'path': 'str', '*arg': ['str'], '*env': ['str'],
-               '*input-data': 'str', '*capture-output': 
'GuestExecCaptureOutput' },
+               '*input-data': 'str', '*capture-output': 
'GuestExecCaptureOutput',
+               '*stream-output': 'bool' },
   'returns': 'GuestExec' }
 
 
-- 
2.41.0