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>

diff --git a/block/blk.h b/block/blk.h
index 3a3d715bd7253b82522b30fcde33161f909dcf0b..fde8b351c166dbdaca88faac146c6f4bf7bf5d9f 100644 (file)
--- a/block/blk.h
+++ b/block/blk.h
@@ -204,6 +204,8 @@ static inline void elv_deactivate_rq(struct request_queue *q, struct request *rq
                e->type->ops.sq.elevator_deactivate_req_fn(q, rq);
 }
 
+struct hd_struct *__disk_get_part(struct gendisk *disk, int partno);
+
 #ifdef CONFIG_FAIL_IO_TIMEOUT
 int blk_should_fake_timeout(struct request_queue *);
 ssize_t part_timeout_show(struct device *, struct device_attribute *, char *);

diff --git a/block/genhd.c b/block/genhd.c
index 3380a1e73ea0a69cd39d104bd714b8689c575b93..713b7d4fe7a1153f078eb70a92ae23a92a84b104 100644 (file)
--- 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;