Re: [PATCH] qga/commands-posix: Make ga_wait_child() return boolean

[Philippe Mathieu-Daudé]

On 15/7/24 11:59, Zhao Liu wrote:

As the comment in qapi/error, dereferencing @errp requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
* - It must not be dereferenced, because it may be null.
...
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.
*
* Using it when it's not needed is safe, but please avoid cluttering
* the source with useless code.

Though currently ga_run_command() only gets &local_err instead of NULL
@errp, it's still better to follow the requirement to add the
ERRP_GUARD().

But as error.h suggested, the best practice for callee is to return
something to indicate success / failure.

So make ga_wait_child() return boolean and check the returned boolean in
ga_run_command() instead of dereferencing @errp, which eliminates the
need of ERRP_GUARD().

I'd avoid mentioning ERRP_GUARD and just describe:

  Make ga_wait_child() return boolean and check the returned boolean
  in ga_run_command() instead of dereferencing @errp.

For the code change:

Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>

Cc: Michael Roth <michael.r...@amd.com>
Cc: Konstantin Kostiuk <kkost...@redhat.com>
Signed-off-by: Zhao Liu <zhao1....@intel.com>
---
  qga/commands-posix.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 7f05996495a2..64bb0be94479 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -59,7 +59,7 @@
  #endif
  #endif

-static void ga_wait_child(pid_t pid, int *status, Error **errp)

+static bool ga_wait_child(pid_t pid, int *status, Error **errp)
  {
      pid_t rpid;

@@ -70,10 +70,11 @@ static void ga_wait_child(pid_t pid, int *status, Error **errp)

      if (rpid == -1) {
          error_setg_errno(errp, errno, "failed to wait for child (pid: %d)",
                           pid);
-        return;
+        return false;
      }

g_assert(rpid == pid);

+    return true;
  }

static ssize_t ga_pipe_read_str(int fd[2], char **str)

@@ -178,8 +179,7 @@ static int ga_run_command(const char *argv[], const char 
*in_str,
          goto out;
      }

- ga_wait_child(pid, &status, errp);

-    if (*errp) {
+    if (!ga_wait_child(pid, &status, errp)) {
          goto out;
      }