block: add a __disk_get_part helper

This helper allows looking up a partion under RCU protection without
grabbing a reference to it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 13 insertions, 13 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 3380a1e73ea0..713b7d4fe7a1 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -82,6 +82,15 @@ void part_in_flight(struct request_queue *q, struct hd_struct *part,
         }
 }
 
+struct hd_struct *__disk_get_part(struct gendisk *disk, int partno)
+{
+        struct disk_part_tbl *ptbl = rcu_dereference(disk->part_tbl);
+
+        if (unlikely(partno < 0 || partno >= ptbl->len))
+                return NULL;
+        return rcu_dereference(ptbl->part[partno]);
+}
+
 /**
  * disk_get_part - get partition
  * @disk: disk to look partition from
@@ -98,21 +107,12 @@ void part_in_flight(struct request_queue *q, struct hd_struct *part,
  */
 struct hd_struct *disk_get_part(struct gendisk *disk, int partno)
 {
-        struct hd_struct *part = NULL;
-        struct disk_part_tbl *ptbl;
-
-        if (unlikely(partno < 0))
-                return NULL;
+        struct hd_struct *part;
 
         rcu_read_lock();
-
-        ptbl = rcu_dereference(disk->part_tbl);
-        if (likely(partno < ptbl->len)) {
-                part = rcu_dereference(ptbl->part[partno]);
-                if (part)
-                        get_device(part_to_dev(part));
-        }
-
+        part = __disk_get_part(disk, partno);
+        if (part)
+                get_device(part_to_dev(part));
         rcu_read_unlock();
 
         return part;