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@xxxxxxxx>
Signed-off-by: Nadia Derbey <Nadia.Derbey@xxxxxxxx>
---
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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