dm bio prison: add dm_cell_promote_or_release()
Rather than always releasing the prisoners in a cell, the client may
want to promote one of them to be the new holder. There is a race here
though between releasing an empty cell, and other threads adding new
inmates. So this function makes the decision with its lock held.
This function can have two outcomes:
i) An inmate is promoted to be the holder of the cell (return value of 0).
ii) The cell has no inmate for promotion and is released (return value of 1).
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index be06530..cd6d1d2 100644
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -255,6 +255,32 @@
}
EXPORT_SYMBOL_GPL(dm_cell_visit_release);
+static int __promote_or_release(struct dm_bio_prison *prison,
+ struct dm_bio_prison_cell *cell)
+{
+ if (bio_list_empty(&cell->bios)) {
+ rb_erase(&cell->node, &prison->cells);
+ return 1;
+ }
+
+ cell->holder = bio_list_pop(&cell->bios);
+ return 0;
+}
+
+int dm_cell_promote_or_release(struct dm_bio_prison *prison,
+ struct dm_bio_prison_cell *cell)
+{
+ int r;
+ unsigned long flags;
+
+ spin_lock_irqsave(&prison->lock, flags);
+ r = __promote_or_release(prison, cell);
+ spin_unlock_irqrestore(&prison->lock, flags);
+
+ return r;
+}
+EXPORT_SYMBOL_GPL(dm_cell_promote_or_release);
+
/*----------------------------------------------------------------*/
#define DEFERRED_SET_SIZE 64