NFSv4.1/flexfiles: RW layouts are valid only if all mirrors are valid

Unlike read layouts, the writeable layout cannot fall back to using only
one of the mirrors. It need to write to all of them.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayoutdev.c

@@ -528,11 +528,11 @@ int ff_layout_encode_ds_ioerr(struct nfs4_flexfile_layout *flo,
 	return 0;
 }
 
-bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg)
+static bool ff_read_layout_has_available_ds(struct pnfs_layout_segment *lseg)
 {
 	struct nfs4_ff_layout_mirror *mirror;
 	struct nfs4_deviceid_node *devid;
-	int idx;
+	u32 idx;
 
 	for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) {
 		mirror = FF_LAYOUT_COMP(lseg, idx);
@@ -546,6 +546,32 @@ bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg)
 	return false;
 }
 
+static bool ff_rw_layout_has_available_ds(struct pnfs_layout_segment *lseg)
+{
+	struct nfs4_ff_layout_mirror *mirror;
+	struct nfs4_deviceid_node *devid;
+	u32 idx;
+
+	for (idx = 0; idx < FF_LAYOUT_MIRROR_COUNT(lseg); idx++) {
+		mirror = FF_LAYOUT_COMP(lseg, idx);
+		if (!mirror || !mirror->mirror_ds)
+			return false;
+		devid = &mirror->mirror_ds->id_node;
+		if (ff_layout_test_devid_unavailable(devid))
+			return false;
+	}
+
+	return FF_LAYOUT_MIRROR_COUNT(lseg) != 0;
+}
+
+bool ff_layout_has_available_ds(struct pnfs_layout_segment *lseg)
+{
+	if (lseg->pls_range.iomode == IOMODE_READ)
+		return  ff_read_layout_has_available_ds(lseg);
+	/* Note: RW layout needs all mirrors available */
+	return ff_rw_layout_has_available_ds(lseg);
+}
+
 module_param(dataserver_retrans, uint, 0644);
 MODULE_PARM_DESC(dataserver_retrans, "The  number of times the NFSv4.1 client "
 			"retries a request before it attempts further "