block/nvme: clarify that free_req_queue is protected by q->lock

Existing users access free_req_queue under q->lock. Document this.

Signed-off-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Sergio Lopez <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: [email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>

Author: stefanhaRH

block/nvme.c

@@ -57,14 +57,14 @@ typedef struct {
 } NVMeRequest;
 
 typedef struct {
-    CoQueue     free_req_queue;
     QemuMutex   lock;
 
     /* Fields protected by BQL */
     int         index;
     uint8_t     *prp_list_pages;
 
     /* Fields protected by @lock */
+    CoQueue     free_req_queue;
     NVMeQueue   sq, cq;
     int         cq_phase;
     int         free_req_head;