drbd: announce FLUSH/FUA capability to upper layers

Unconditionally announce FLUSH/FUA to upper layers.
If the lower layers on either node do not actually support this,
generic_make_request() will deal with it.

If this causes performance regressions on your setup,
make sure there are no volatile caches involved,
and mount -o nobarrier or equivalent.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 6ace11e9e5a1..3fbef018ce55 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -876,7 +876,11 @@ int __drbd_set_out_of_sync(struct drbd_conf *mdev, sector_t sector, int size,
         unsigned int enr, count = 0;
         struct lc_element *e;
 
-        if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
+        /* this should be an empty REQ_FLUSH */
+        if (size == 0)
+                return 0;
+
+        if (size < 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
                 dev_err(DEV, "sector: %llus, size: %d\n",
                         (unsigned long long)sector, size);
                 return 0;