pNFS/flexfiles: Add support for FF_FLAGS_NO_IO_THRU_MDS

For loosely coupled pNFS/flexfiles systems, there is often no advantage
at all in going through the MDS for I/O, since the MDS is subject to
the same limitations as all other clients when talking to DSes. If a
DS is unresponsive, I/O through the MDS will fail.

For such systems, the only scalable solution is to have the pNFS clients
retry doing pNFS, and so the protocol now provides a flag that allows
the pNFS server to signal this.

If LAYOUTGET returns FF_FLAGS_NO_IO_THRU_MDS, then we should assume that
the MDS wants the client to retry using these devices, even if they were
previously marked as being unavailable. To do so, we add a helper,
ff_layout_mark_devices_valid() that will be called from layoutget.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h b/fs/nfs/flexfilelayout/flexfilelayout.h
index 68cc0d9828f9..2bb08bc6aaf0 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -10,6 +10,7 @@
 #define FS_NFS_NFS4FLEXFILELAYOUT_H
 
 #define FF_FLAGS_NO_LAYOUTCOMMIT 1
+#define FF_FLAGS_NO_IO_THRU_MDS 2
 
 #include "../pnfs.h"
 
@@ -146,6 +147,12 @@ FF_LAYOUT_MIRROR_COUNT(struct pnfs_layout_segment *lseg)
 }
 
 static inline bool
+ff_layout_no_fallback_to_mds(struct pnfs_layout_segment *lseg)
+{
+	return FF_LAYOUT_LSEG(lseg)->flags & FF_FLAGS_NO_IO_THRU_MDS;
+}
+
+static inline bool
 ff_layout_test_devid_unavailable(struct nfs4_deviceid_node *node)
 {
 	return nfs4_test_deviceid_unavailable(node);