> On Feb 18, 2016, at 12:44 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 24 ++++++++++++++++--------
> include/linux/sunrpc/auth.h | 7 +++++++
> net/sunrpc/auth_null.c | 4 ++--
> net/sunrpc/auth_unix.c | 6 ++----
> 4 files changed, 27 insertions(+), 14 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index c484a2b..0f56e57 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -2586,21 +2586,29 @@ static __be32 check_forechannel_attrs(struct nfsd4_channel_attrs *ca, struct nfs
> return nfs_ok;
> }
>
> +/*
> + * Server's NFSv4.1 backchannel support is AUTH_SYS-only for now.
> + * These are based on similar macros in linux/sunrpc/msg_prot.h .
> + */
> +#define RPC_MAX_HEADER_WITH_AUTH_SYS \
> + (RPC_CALLHDRSIZE + 2 * (2 + UNX_CALLSLACK))
> +
> +#define RPC_MAX_REPHEADER_WITH_AUTH_SYS \
> + (RPC_REPHDRSIZE + (2 + NUL_REPLYSLACK))
> +
> #define NFSD_CB_MAX_REQ_SZ ((NFS4_enc_cb_recall_sz + \
> - RPC_MAX_HEADER_WITH_AUTH) * sizeof(__be32))
> + RPC_MAX_HEADER_WITH_AUTH_SYS) * sizeof(__be32))
> #define NFSD_CB_MAX_RESP_SZ ((NFS4_dec_cb_recall_sz + \
> - RPC_MAX_REPHEADER_WITH_AUTH) * sizeof(__be32))
> + RPC_MAX_REPHEADER_WITH_AUTH_SYS) * \
> + sizeof(__be32))
>
> static __be32 check_backchannel_attrs(struct nfsd4_channel_attrs *ca)
> {
> ca->headerpadsz = 0;
>
> - /*
> - * These RPC_MAX_HEADER macros are overkill, especially since we
> - * don't even do gss on the backchannel yet. But this is still
> - * less than 1k. Tighten up this estimate in the unlikely event
> - * it turns out to be a problem for some client:
> - */
> + pr_err("%s: NFSD_CB_MAX_REQ_SZ=%lu, NFSD_CB_MAX_RESP_SZ=%lu\n",
> + __func__, NFSD_CB_MAX_REQ_SZ, NFSD_CB_MAX_RESP_SZ);
> +
Oops, forgot to remove this pr_err. That will be gone in the
next version of this patch.
> if (ca->maxreq_sz < NFSD_CB_MAX_REQ_SZ)
> return nfserr_toosmall;
> if (ca->maxresp_sz < NFSD_CB_MAX_RESP_SZ)
> diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
> index 1ecf13e..6a241a2 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;
>
> diff --git a/net/sunrpc/auth_null.c b/net/sunrpc/auth_null.c
> index c2a2b58..8d9eb4d 100644
> --- a/net/sunrpc/auth_null.c
> +++ b/net/sunrpc/auth_null.c
> @@ -113,8 +113,8 @@ const struct rpc_authops authnull_ops = {
>
> static
> struct rpc_auth null_auth = {
> - .au_cslack = 4,
> - .au_rslack = 2,
> + .au_cslack = NUL_CALLSLACK,
> + .au_rslack = NUL_REPLYSLACK,
> .au_ops = &authnull_ops,
> .au_flavor = RPC_AUTH_NULL,
> .au_count = ATOMIC_INIT(0),
> diff --git a/net/sunrpc/auth_unix.c b/net/sunrpc/auth_unix.c
> index 548240d..0d3dd36 100644
> --- a/net/sunrpc/auth_unix.c
> +++ b/net/sunrpc/auth_unix.c
> @@ -23,8 +23,6 @@ struct unx_cred {
> };
> #define uc_uid uc_base.cr_uid
>
> -#define UNX_WRITESLACK (21 + XDR_QUADLEN(UNX_MAXNODENAME))
> -
> #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
> # define RPCDBG_FACILITY RPCDBG_AUTH
> #endif
> @@ -228,8 +226,8 @@ const struct rpc_authops authunix_ops = {
>
> static
> struct rpc_auth unix_auth = {
> - .au_cslack = UNX_WRITESLACK,
> - .au_rslack = 2, /* assume AUTH_NULL verf */
> + .au_cslack = UNX_CALLSLACK,
> + .au_rslack = NUL_REPLYSLACK,
> .au_ops = &authunix_ops,
> .au_flavor = RPC_AUTH_UNIX,
> .au_count = ATOMIC_INIT(0),
>
> --
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--
Chuck Lever
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