IB/mthca: Avoid changing userspace ABI to handle DMA write barrier attribute

Commit cb9fbc5c ("IB: expand ib_umem_get() prototype") changed the
mthca userspace ABI to provide a way for userspace to indicate which
memory regions need the DMA write barrier attribute.  However, it is
possible to handle this without breaking existing userspace, by having
the mthca kernel driver recognize whether it is talking to old or new
userspace, depending on the size of the register MR structure passed in.

The only potential drawback of this is that is allows old userspace
(which has a bug with DMA ordering on large SGI Altix systems) to
continue to run on new kernels, but the advantage of allowing old
userspace to continue to work on unaffected systems seems to outweigh
this, and we can print a warning to push people to upgrade their
userspace.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_provider.h b/drivers/infiniband/hw/mthca/mthca_provider.h
index 262616c8ebb6..934bf9544037 100644
--- a/drivers/infiniband/hw/mthca/mthca_provider.h
+++ b/drivers/infiniband/hw/mthca/mthca_provider.h
@@ -67,6 +67,7 @@ struct mthca_ucontext {
         struct ib_ucontext          ibucontext;
         struct mthca_uar            uar;
         struct mthca_user_db_table *db_tab;
+        int                         reg_mr_warned;
 };
 
 struct mthca_mtt;