ipc: introduce the ipcid_to_idx macro

This is a trivial patch that changes all the (id % SEQ_MULTIPLIER) into a call
to the ipcid_to_idx(id) macro.
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/util.c

@@ -413,7 +413,7 @@ int ipcget_public(struct ipc_namespace *ns, struct ipc_ids *ids,
  
 void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
 {
-	int lid = ipcp->id % SEQ_MULTIPLIER;
+	int lid = ipcid_to_idx(ipcp->id);
 
 	idr_remove(&ids->ipcs_idr, lid);
 
@@ -672,7 +672,7 @@ void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
 struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
 {
 	struct kern_ipc_perm *out;
-	int lid = id % SEQ_MULTIPLIER;
+	int lid = ipcid_to_idx(id);
 
 	rcu_read_lock();
 	out = idr_find(&ids->ipcs_idr, lid);

ipc/util.h

@@ -79,6 +79,8 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
 #define IPC_MSG_IDS	1
 #define IPC_SHM_IDS	2
 
+#define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
+
 /* must be called with ids->mutex acquired.*/
 int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
 int ipc_get_maxid(struct ipc_ids *);