[PATCH v2 1/7] hw/cxl/cxl-host: Fix missing ERRP_GUARD() in cxl_fixed_memory_window_config()

[Zhao Liu <zhao1.liu@linux.intel.com>]

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

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.

But in cxl_fixed_memory_window_config(), @errp is dereferenced in 2
places without ERRP_GUARD():

fw->enc_int_ways = cxl_interleave_ways_enc(fw->num_targets, errp);
if (*errp) {
    return;
}

and

fw->enc_int_gran =
    cxl_interleave_granularity_enc(object->interleave_granularity,
                                   errp);
if (*errp) {
    return;
}

For the above 2 places, we check "*errp", because neither function
returns a suitable error code. And since machine_set_cfmw() - the caller
of cxl_fixed_memory_window_config() - doesn't get the NULL @errp
parameter as the "set" method of object property,
cxl_fixed_memory_window_config() hasn't triggered the bug that
dereferencing the NULL @errp.

To follow the requirement of @errp, add missing ERRP_GUARD() in
cxl_fixed_memory_window_config().

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
---
Suggested by credit:
 Markus: Referred his explanation about ERRP_GUARD().
---
v2:
 * Add the @errp dereference code in commit message to make review
   easier. (Markus)
---
 hw/cxl/cxl-host.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
index 2aa776c79c74..c5f5fcfd64d0 100644
--- a/hw/cxl/cxl-host.c
+++ b/hw/cxl/cxl-host.c
@@ -26,6 +26,7 @@ static void cxl_fixed_memory_window_config(CXLState *cxl_state,
                                            CXLFixedMemoryWindowOptions *object,
                                            Error **errp)
 {
+    ERRP_GUARD();
     g_autofree CXLFixedWindow *fw = g_malloc0(sizeof(*fw));
     strList *target;
     int i;
-- 
2.34.1