linux-kernel - [PATCH 01/11] ipc,shm: introduce lockless functions to obtain the ipc object

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Date:	Tue, 18 Jun 2013 18:18:26 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	akpm@...ux-foundation.org, riel@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>
Subject: [PATCH 01/11] ipc,shm: introduce lockless functions to obtain the ipc object

Add shm_obtain_object() and shm_obtain_object_check(), which will allow us
to get the ipc object without acquiring the lock. Just as with other forms
of ipc, these functions are basically wrappers around ipc_obtain_object*().

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
---
 ipc/shm.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/ipc/shm.c b/ipc/shm.c
index c6b4ad5..216ae72 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -124,6 +124,26 @@ void __init shm_init (void)
 				IPC_SHM_IDS, sysvipc_shm_proc_show);
 }
 
+static inline struct shmid_kernel *shm_obtain_object(struct ipc_namespace *ns, int id)
+{
+	struct kern_ipc_perm *ipcp = ipc_obtain_object(&shm_ids(ns), id);
+
+	if (IS_ERR(ipcp))
+		return ERR_CAST(ipcp);
+
+	return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
+static inline struct shmid_kernel *shm_obtain_object_check(struct ipc_namespace *ns, int id)
+{
+	struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&shm_ids(ns), id);
+
+	if (IS_ERR(ipcp))
+		return ERR_CAST(ipcp);
+
+	return container_of(ipcp, struct shmid_kernel, shm_perm);
+}
+
 /*
  * shm_lock_(check_) routines are called in the paths where the rw_mutex
  * is not necessarily held.
-- 
1.7.11.7

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