svc: Add transport hdr size for defer/revisit

Some transports have a header in front of the RPC header. The current
defer/revisit processing considers only the iov_len and arg_len to
determine how much to back up when saving the original request
to revisit. Add a field to the rqstp structure to save the size
of the transport header so svc_defer can correctly compute
the start of a request.

Signed-off-by: Tom Tucker <[e-mail]>
Acked-by: Neil Brown <[e-mail]>
Reviewed-by: Chuck Lever <[e-mail]>
Reviewed-by: Greg Banks <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

include/linux/sunrpc/svc.h

···
 	void *			rq_xprt_ctxt;	/* transport specific context ptr */
 	struct svc_deferred_req*rq_deferred;	/* deferred request we are replaying */
 
+	size_t			rq_xprt_hlen;	/* xprt header len */
 	struct xdr_buf		rq_arg;
 	struct xdr_buf		rq_res;
 	struct page *		rq_pages[RPCSVC_MAXPAGES];
···
 	size_t			addrlen;
 	union svc_addr_u	daddr;	/* where reply must come from */
 	struct cache_deferred_req handle;
+	size_t			xprt_hlen;
 	int			argslen;
 	__be32			args[0];
 };

net/sunrpc/svc_xprt.c

···
 #include <linux/sunrpc/types.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/xdr.h>
-#include <linux/sunrpc/svcsock.h>
 #include <linux/sunrpc/stats.h>
 #include <linux/sunrpc/svc_xprt.h>
 
···
 	svc_xprt_put(xprt);
 }
 
+/*
+ * Save the request off for later processing. The request buffer looks
+ * like this:
+ *
+ * <xprt-header><rpc-header><rpc-pagelist><rpc-tail>
+ *
+ * This code can only handle requests that consist of an xprt-header
+ * and rpc-header.
+ */
 static struct cache_deferred_req *svc_defer(struct cache_req *req)
 {
 	struct svc_rqst *rqstp = container_of(req, struct svc_rqst, rq_chandle);
-	int size = sizeof(struct svc_deferred_req) + (rqstp->rq_arg.len);
 	struct svc_deferred_req *dr;
 
 	if (rqstp->rq_arg.page_len)
···
 		dr = rqstp->rq_deferred;
 		rqstp->rq_deferred = NULL;
 	} else {
-		int skip  = rqstp->rq_arg.len - rqstp->rq_arg.head[0].iov_len;
+		size_t skip;
+		size_t size;
 		/* FIXME maybe discard if size too large */
+		size = sizeof(struct svc_deferred_req) + rqstp->rq_arg.len;
 		dr = kmalloc(size, GFP_KERNEL);
 		if (dr == NULL)
 			return NULL;
···
 		dr->addrlen = rqstp->rq_addrlen;
 		dr->daddr = rqstp->rq_daddr;
 		dr->argslen = rqstp->rq_arg.len >> 2;
-		memcpy(dr->args, rqstp->rq_arg.head[0].iov_base-skip,
-		       dr->argslen<<2);
+		dr->xprt_hlen = rqstp->rq_xprt_hlen;
+
+		/* back up head to the start of the buffer and copy */
+		skip = rqstp->rq_arg.len - rqstp->rq_arg.head[0].iov_len;
+		memcpy(dr->args, rqstp->rq_arg.head[0].iov_base - skip,
+		       dr->argslen << 2);
 	}
 	svc_xprt_get(rqstp->rq_xprt);
 	dr->xprt = rqstp->rq_xprt;
···
 {
 	struct svc_deferred_req *dr = rqstp->rq_deferred;
 
-	rqstp->rq_arg.head[0].iov_base = dr->args;
-	rqstp->rq_arg.head[0].iov_len = dr->argslen<<2;
+	/* setup iov_base past transport header */
+	rqstp->rq_arg.head[0].iov_base = dr->args + (dr->xprt_hlen>>2);
+	/* The iov_len does not include the transport header bytes */
+	rqstp->rq_arg.head[0].iov_len = (dr->argslen<<2) - dr->xprt_hlen;
 	rqstp->rq_arg.page_len = 0;
-	rqstp->rq_arg.len = dr->argslen<<2;
+	/* The rq_arg.len includes the transport header bytes */
+	rqstp->rq_arg.len     = dr->argslen<<2;
 	rqstp->rq_prot        = dr->prot;
 	memcpy(&rqstp->rq_addr, &dr->addr, dr->addrlen);
 	rqstp->rq_addrlen     = dr->addrlen;
+	/* Save off transport header len in case we get deferred again */
+	rqstp->rq_xprt_hlen   = dr->xprt_hlen;
 	rqstp->rq_daddr       = dr->daddr;
 	rqstp->rq_respages    = rqstp->rq_pages;
-	return dr->argslen<<2;
+	return (dr->argslen<<2) - dr->xprt_hlen;
 }
 
 

net/sunrpc/svcsock.c

···
 	};
 	int len;
 
+	rqstp->rq_xprt_hlen = 0;
+
 	len = kernel_recvmsg(svsk->sk_sock, &msg, iov, nr, buflen,
 				msg.msg_flags);