Re: [Qemu-devel] [PATCH v2 11/15] qga: Clean up fragile use of error_is_set()

[Michael Roth]

Quoting Markus Armbruster (2014-04-28 15:27:50)
> Using error_is_set(ERRP) to find out whether a function failed is
> either wrong, fragile, or unnecessarily opaque.  It's wrong when ERRP
> may be null, because errors go undetected when it is.  It's fragile
> when proving ERRP non-null involves a non-local argument.  Else, it's
> unnecessarily opaque (see commit 84d18f0).
> 
> The error_is_set(errp) in the guest agent command handler functions
> are merely fragile, because all chall chains (do_qmp_dispatch() via
> the generated marshalling functions) pass a non-null errp argument.
> 
> Make the code more robust and more obviously correct: receive the
> error in a local variable, then propagate it through the parameter.
> 
> Signed-off-by: Markus Armbruster <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>

Reviewed-by: Michael Roth <address@hidden>

> ---
>  qga/commands-posix.c | 22 ++++++++++++++++------
>  qga/commands-win32.c | 38 ++++++++++++++++++++++++--------------
>  2 files changed, 40 insertions(+), 20 deletions(-)
> 
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 6af974f..34ddba0 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -1067,8 +1067,11 @@ out:
> 
>  void qmp_guest_suspend_disk(Error **errp)
>  {
> -    bios_supports_mode("pm-is-supported", "--hibernate", "disk", errp);
> -    if (error_is_set(errp)) {
> +    Error *local_err = NULL;
> +
> +    bios_supports_mode("pm-is-supported", "--hibernate", "disk", &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          return;
>      }
> 
> @@ -1077,8 +1080,11 @@ void qmp_guest_suspend_disk(Error **errp)
> 
>  void qmp_guest_suspend_ram(Error **errp)
>  {
> -    bios_supports_mode("pm-is-supported", "--suspend", "mem", errp);
> -    if (error_is_set(errp)) {
> +    Error *local_err = NULL;
> +
> +    bios_supports_mode("pm-is-supported", "--suspend", "mem", &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          return;
>      }
> 
> @@ -1087,8 +1093,12 @@ void qmp_guest_suspend_ram(Error **errp)
> 
>  void qmp_guest_suspend_hybrid(Error **errp)
>  {
> -    bios_supports_mode("pm-is-supported", "--suspend-hybrid", NULL, errp);
> -    if (error_is_set(errp)) {
> +    Error *local_err = NULL;
> +
> +    bios_supports_mode("pm-is-supported", "--suspend-hybrid", NULL,
> +                       &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          return;
>      }
> 
> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
> index d0d8504..3483c0d 100644
> --- a/qga/commands-win32.c
> +++ b/qga/commands-win32.c
> @@ -87,6 +87,7 @@ static void execute_async(DWORD WINAPI (*func)(LPVOID), 
> LPVOID opaque,
> 
>  void qmp_guest_shutdown(bool has_mode, const char *mode, Error **errp)
>  {
> +    Error *local_err = NULL;
>      UINT shutdown_flag = EWX_FORCE;
> 
>      slog("guest-shutdown called, mode: %s", mode);
> @@ -105,8 +106,9 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, 
> Error **errp)
> 
>      /* Request a shutdown privilege, but try to shut down the system
>         anyway. */
> -    acquire_privilege(SE_SHUTDOWN_NAME, errp);
> -    if (error_is_set(errp)) {
> +    acquire_privilege(SE_SHUTDOWN_NAME, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          return;
>      }
> 
> @@ -191,14 +193,16 @@ int64_t qmp_guest_fsfreeze_freeze(Error **errp)
>      /* cannot risk guest agent blocking itself on a write in this state */
>      ga_set_frozen(ga_state);
> 
> -    qga_vss_fsfreeze(&i, errp, true);
> -    if (error_is_set(errp)) {
> +    qga_vss_fsfreeze(&i, &local_err, true);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          goto error;
>      }
> 
>      return i;
> 
>  error:
> +    local_err = NULL;
>      qmp_guest_fsfreeze_thaw(&local_err);
>      if (local_err) {
>          g_debug("cleanup thaw: %s", error_get_pretty(local_err));
> @@ -313,28 +317,32 @@ static DWORD WINAPI do_suspend(LPVOID opaque)
> 
>  void qmp_guest_suspend_disk(Error **errp)
>  {
> +    Error *local_err = NULL;
>      GuestSuspendMode *mode = g_malloc(sizeof(GuestSuspendMode));
> 
>      *mode = GUEST_SUSPEND_MODE_DISK;
> -    check_suspend_mode(*mode, errp);
> -    acquire_privilege(SE_SHUTDOWN_NAME, errp);
> -    execute_async(do_suspend, mode, errp);
> +    check_suspend_mode(*mode, &local_err);
> +    acquire_privilege(SE_SHUTDOWN_NAME, &local_err);
> +    execute_async(do_suspend, mode, &local_err);
> 
> -    if (error_is_set(errp)) {
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          g_free(mode);
>      }
>  }
> 
>  void qmp_guest_suspend_ram(Error **errp)
>  {
> +    Error *local_err = NULL;
>      GuestSuspendMode *mode = g_malloc(sizeof(GuestSuspendMode));
> 
>      *mode = GUEST_SUSPEND_MODE_RAM;
> -    check_suspend_mode(*mode, errp);
> -    acquire_privilege(SE_SHUTDOWN_NAME, errp);
> -    execute_async(do_suspend, mode, errp);
> +    check_suspend_mode(*mode, &local_err);
> +    acquire_privilege(SE_SHUTDOWN_NAME, &local_err);
> +    execute_async(do_suspend, mode, &local_err);
> 
> -    if (error_is_set(errp)) {
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          g_free(mode);
>      }
>  }
> @@ -375,6 +383,7 @@ int64_t qmp_guest_get_time(Error **errp)
> 
>  void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
>  {
> +    Error *local_err = NULL;
>      SYSTEMTIME ts;
>      FILETIME tf;
>      LONGLONG time;
> @@ -406,8 +415,9 @@ void qmp_guest_set_time(bool has_time, int64_t time_ns, 
> Error **errp)
>          }
>      }
> 
> -    acquire_privilege(SE_SYSTEMTIME_NAME, errp);
> -    if (error_is_set(errp)) {
> +    acquire_privilege(SE_SYSTEMTIME_NAME, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
>          return;
>      }
> 
> -- 
> 1.8.1.4