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.

---
 fs/nfs/flexfilelayout/flexfilelayout.c | 18 ++++++++++++++++-- fs/nfs/flexfilelayout/flexfilelayout.h |  7 +++++++

 2 files changed, 23 insertions(+), 2 deletions(-)

b/fs/nfs/flexfilelayout/flexfilelayout.c
index 7fc14b90886e..03516c80855a 100644

@@ -339,6 +339,19 @@ static void ff_layout_sort_mirrors(struct

nfs4_ff_layout_segment *fls)
  }
 }

+static void ff_layout_mark_devices_valid(struct nfs4_ff_layout_segment *fls)
+{
+ struct nfs4_deviceid_node *node;
+ int i;
+
+ if (!(fls->flags & FF_FLAGS_NO_IO_THRU_MDS))
+ return;
+ for (i = 0; i < fls->mirror_array_cnt; i++) {
+ node = &fls->mirror_array[i]->mirror_ds->id_node;
+ clear_bit(NFS_DEVICEID_UNAVAILABLE, &node->flags);
+ }
+}
+
 static struct pnfs_layout_segment * ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
       struct nfs4_layoutget_res *lgr,
@@ -499,6 +512,7 @@ ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh, rc = ff_layout_check_layout(lgr);
  if (rc)
  goto out_err_free;
+ ff_layout_mark_devices_valid(fls);

  ret = &fls->generic_hdr;
  dprintk("<-- %s (success)\n", __func__);
@@ -1035,7 +1049,8 @@ static int ff_layout_async_handle_error_v4(struct rpc_task *task,
  rpc_wake_up(&tbl->slot_tbl_waitq);
  /* fall through */
  default:
- if (ff_layout_has_available_ds(lseg))
+ if (ff_layout_no_fallback_to_mds(lseg) ||
+     ff_layout_has_available_ds(lseg))
  return -NFS4ERR_RESET_TO_PNFS; reset:
  dprintk("%s Retry through MDS. Error %d\n", __func__, @@ -1153,7 +1168,6 @@ static void ff_layout_io_track_ds_error(struct pnfs_layout_segment *lseg,
 }

 /* NFS_PROTO call done callback routines */
-
 static int ff_layout_read_done_cb(struct rpc_task *task, struct nfs_pgio_header *hdr) {

b/fs/nfs/flexfilelayout/flexfilelayout.h
index 68cc0d9828f9..2bb08bc6aaf0 100644

@@ -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);