From: Zhao Liu <zhao1.liu@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* 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.

ERRP_GUARD() could avoid the case when @errp is the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

The migrate_params_check() passes @errp to error_prepend() without
ERRP_GUARD(), and it could be called from migration_object_init(),
where the passed @errp points to @error_fatal.

Therefore, the error message echoed in error_prepend() will be lost
because of the above issue.

To fix this, add missing ERRP_GUARD() at the beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: Peter Xu <peterx@redhat.com>
Cc: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 migration/options.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/migration/options.c b/migration/options.c
index 3e3e0b93b439..b98cd639979e 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -1057,6 +1057,8 @@ void migrate_params_init(MigrationParameters *params)
  */
 bool migrate_params_check(MigrationParameters *params, Error **errp)
 {
+    ERRP_GUARD();
+
     if (params->has_compress_level &&
         (params->compress_level > 9)) {
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "compress_level",
-- 
2.34.1

On Thu, Feb 29, 2024 at 10:39:11PM +0800, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> As the comment in qapi/error, passing @errp to error_prepend() requires
> ERRP_GUARD():
> 
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> ...
> * - It should not be passed to error_prepend(), error_vprepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * 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.
> 
> ERRP_GUARD() could avoid the case when @errp is the pointer of
> error_fatal, the user can't see this additional information, because
> exit() happens in error_setg earlier than information is added [1].
> 
> The migrate_params_check() passes @errp to error_prepend() without
> ERRP_GUARD(), and it could be called from migration_object_init(),
> where the passed @errp points to @error_fatal.
> 
> Therefore, the error message echoed in error_prepend() will be lost
> because of the above issue.
> 
> To fix this, add missing ERRP_GUARD() at the beginning of this function.
> 
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>      ("error: New macro ERRP_GUARD()").
> 
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Fabiano Rosas <farosas@suse.de>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>

Acked-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Zhao Liu <zhao1.liu@linux.intel.com> writes:

> From: Zhao Liu <zhao1.liu@intel.com>
>
> As the comment in qapi/error, passing @errp to error_prepend() requires
> ERRP_GUARD():
>
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> ...
> * - It should not be passed to error_prepend(), error_vprepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * 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.
>
> ERRP_GUARD() could avoid the case when @errp is the pointer of
> error_fatal, the user can't see this additional information, because
> exit() happens in error_setg earlier than information is added [1].
>
> The migrate_params_check() passes @errp to error_prepend() without
> ERRP_GUARD(), and it could be called from migration_object_init(),
> where the passed @errp points to @error_fatal.
>
> Therefore, the error message echoed in error_prepend() will be lost
> because of the above issue.
>
> To fix this, add missing ERRP_GUARD() at the beginning of this function.
>
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>      ("error: New macro ERRP_GUARD()").
>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Fabiano Rosas <farosas@suse.de>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>