[Devel] [RFC PATCH 4/6] IPC/sem: next operations for /proc/pid/semundo

[Nadia.Derbey at bull.net]

PATCH [04/06]

This patch introduces the .next seq operation for /proc/pid/semundo.

What should be mentioned here is that the undo_list lock is released between
between each iteration.
Doing this, we only guarantee to access some valid data during the .show,
not to have a full coherent view of the whole list. But, oth, this reduces the
the performance impact on the access to the undo_list.

Signed-off-by: Pierre Peiffer <pierre.peiffer at bull.net>
Signed-off-by: Nadia Derbey <Nadia.Derbey at bull.net>

---
 ipc/sem.c |   23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

Index: linux-2.6.26-rc5-mm3/ipc/sem.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/ipc/sem.c	2008-06-24 12:32:36.000000000 +0200
+++ linux-2.6.26-rc5-mm3/ipc/sem.c	2008-06-24 12:54:40.000000000 +0200
@@ -1440,7 +1440,28 @@ static void *semundo_start(struct seq_fi
 
 static void *semundo_next(struct seq_file *m, void *v, loff_t *ppos)
 {
-	return NULL;
+	struct sem_undo	*undo = v;
+	struct undo_list_data *data = m->private;
+	struct sem_undo_list *ulp = data->undo_list;
+
+	/*
+	 * No need to protect against ulp being NULL, if we are here,
+	 * it can't be NULL.
+	 */
+	spin_lock(&ulp->lock);
+
+	do {
+		undo = list_entry(rcu_dereference(undo->list_proc.next),
+				struct sem_undo, list_proc);
+
+	} while (&undo->list_proc != &ulp->list_proc && undo->semid == -1);
+
+	++*ppos;
+	spin_unlock(&ulp->lock);
+
+	if (&undo->list_proc == &ulp->list_proc)
+		return NULL;
+	return undo;
 }
 
 static void semundo_stop(struct seq_file *m, void *v)

--
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