PATCH [03/06]
This patch introduces the .start and .stop seq operations for
/proc/pid/semundo.
Signed-off-by: Pierre Peiffer <[EMAIL PROTECTED]>
Signed-off-by: Nadia Derbey <[EMAIL PROTECTED]>
---
ipc/sem.c | 43 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 41 insertions(+), 2 deletions(-)
Index: linux-2.6.26-rc5-mm3/ipc/sem.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/ipc/sem.c 2008-06-24 10:59:46.000000000 +0200
+++ linux-2.6.26-rc5-mm3/ipc/sem.c 2008-06-24 12:32:36.000000000 +0200
@@ -1400,7 +1400,42 @@ struct undo_list_data {
/* iterator */
static void *semundo_start(struct seq_file *m, loff_t *ppos)
{
- return NULL;
+ struct undo_list_data *data = m->private;
+ struct sem_undo_list *ulp = data->undo_list;
+ struct sem_undo *undo;
+ loff_t pos = *ppos;
+
+ if (!ulp)
+ return NULL;
+
+ if (pos < 0)
+ return NULL;
+
+ /* If ulp is not NULL, it means that we've successfully grabbed
+ * a refcnt in semundo_open. That prevents the undo_list from being
+ * freed.
+ *
+ * Note:
+ * 1) the sem_undo structure is RCU-protected. So take the rcu read
+ * lock and only release it during the .stop operation.
+ * 2) we accept to release the undo_list lock (i.e. we allow the list
+ * to change) between each iteration, instead of taking that lock
+ * during the .start and releasing it during the .stop operation.
+ * This is to reduce the performance impact on the access to the
+ * undo_list.
+ */
+ rcu_read_lock();
+ spin_lock(&ulp->lock);
+ list_for_each_entry_rcu(undo, &ulp->list_proc, list_proc) {
+ if ((undo->semid != -1) && !(pos--))
+ break;
+ }
+ spin_unlock(&ulp->lock);
+
+ if (&undo->list_proc == &ulp->list_proc)
+ return NULL;
+
+ return undo;
}
static void *semundo_next(struct seq_file *m, void *v, loff_t *ppos)
@@ -1410,7 +1445,11 @@ static void *semundo_next(struct seq_fil
static void semundo_stop(struct seq_file *m, void *v)
{
- return;
+ struct undo_list_data *data = m->private;
+ struct sem_undo_list *ulp = data->undo_list;
+
+ if (ulp)
+ rcu_read_unlock();
}
static int semundo_show(struct seq_file *m, void *v)
--
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