nfsd: Lower NFSv4.1 callback message size limit

The maximum size of a backchannel message on RPC-over-RDMA depends
on the connection's inline threshold. Today that threshold is
typically 1024 bytes, making the maximum message size 996 bytes.

The Linux server's CREATE_SESSION operation checks that the size
of callback Calls can be as large as 1044 bytes, to accommodate
RPCSEC_GSS. Thus CREATE_SESSION fails if a client advertises the
true message size maximum of 996 bytes.

But the server's backchannel currently does not support RPCSEC_GSS.
The actual maximum size it needs is much smaller. It is safe to
reduce the limit to enable NFSv4.1 on RDMA backchannel operation.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 1ecf13e148b8..6a241a277249 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -21,10 +21,17 @@
 #include <linux/utsname.h>
 
 /*
+ * Maximum size of AUTH_NONE authentication information, in XDR words.
+ */
+#define NUL_CALLSLACK	(4)
+#define NUL_REPLYSLACK	(2)
+
+/*
  * Size of the nodename buffer. RFC1831 specifies a hard limit of 255 bytes,
  * but Linux hostnames are actually limited to __NEW_UTS_LEN bytes.
  */
 #define UNX_MAXNODENAME	__NEW_UTS_LEN
+#define UNX_CALLSLACK	(21 + XDR_QUADLEN(UNX_MAXNODENAME))
 
 struct rpcsec_gss_info;