path: root/net/sunrpc/xprt.c

/*
 *  linux/net/sunrpc/xprt.c
 *
 *  This is a generic RPC call interface supporting congestion avoidance,
 *  and asynchronous calls.
 *
 *  The interface works like this:
 *
 *  -	When a process places a call, it allocates a request slot if
 *	one is available. Otherwise, it sleeps on the backlog queue
 *	(xprt_reserve).
 *  -	Next, the caller puts together the RPC message, stuffs it into
 *	the request struct, and calls xprt_transmit().
 *  -	xprt_transmit sends the message and installs the caller on the
 *	transport's wait list. At the same time, if a reply is expected,
 *	it installs a timer that is run after the packet's timeout has
 *	expired.
 *  -	When a packet arrives, the data_ready handler walks the list of
 *	pending requests for that transport. If a matching XID is found, the
 *	caller is woken up, and the timer removed.
 *  -	When no reply arrives within the timeout interval, the timer is
 *	fired by the kernel and runs xprt_timer(). It either adjusts the
 *	timeout values (minor timeout) or wakes up the caller with a status
 *	of -ETIMEDOUT.
 *  -	When the caller receives a notification from RPC that a reply arrived,
 *	it should release the RPC slot, and process the reply.
 *	If the call timed out, it may choose to retry the operation by
 *	adjusting the initial timeout value, and simply calling rpc_call
 *	again.
 *
 *  Support for async RPC is done through a set of RPC-specific scheduling
 *  primitives that `transparently' work for processes as well as async
 *  tasks that rely on callbacks.
 *
 *  Copyright (C) 1995-1997, Olaf Kirch <okir@monad.swb.de>
 *
 *  Transport switch API copyright (C) 2005, Chuck Lever <cel@netapp.com>
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/workqueue.h>
#include <linux/net.h>
#include <linux/ktime.h>

#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/metrics.h>
#include <linux/sunrpc/bc_xprt.h>

#include "sunrpc.h"

/*
 * Local variables
 */

#ifdef RPC_DEBUG
# define RPCDBG_FACILITY	RPCDBG_XPRT
#endif

/*
 * Local functions
 */
static void	 xprt_init(struct rpc_xprt *xprt, struct net *net);
static void	xprt_request_init(struct rpc_task *, struct rpc_xprt *);
static void	xprt_connect_status(struct rpc_task *task);
static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
static void	 xprt_destroy(struct rpc_xprt *xprt);

static DEFINE_SPINLOCK(xprt_list_lock);
static LIST_HEAD(xprt_list);

/*
 * The transport code maintains an estimate on the maximum number of out-
 * standing RPC requests, using a smoothed version of the congestion
 * avoidance implemented in 44BSD. This is basically the Van Jacobson
 * congestion algorithm: If a retransmit occurs, the congestion window is
 * halved; otherwise, it is incremented by 1/cwnd when
 *
 *	-	a reply is received and
 *	-	a full number of requests are outstanding and
 *	-	the congestion window hasn't been updated recently.
 */
#define RPC_CWNDSHIFT		(8U)
#define RPC_CWNDSCALE		(1U << RPC_CWNDSHIFT)
#define RPC_INITCWND		RPC_CWNDSCALE
#define RPC_MAXCWND(xprt)	((xprt)->max_reqs << RPC_CWNDSHIFT)

#define RPCXPRT_CONGESTED(xprt) ((xprt)->cong >= (xprt)->cwnd)

/**
 * xprt_register_transport - register a transport implementation
 * @transport: transport to register
 *
 * If a transport implementation is loaded as a kernel module, it can
 * call this interface to make itself known to the RPC client.
 *
 * Returns:
 * 0:		transport successfully registered
 * -EEXIST:	transport already registered
 * -EINVAL:	transport module being unloaded
 */
int xprt_register_transport(struct xprt_class *transport)
{
	struct xprt_class *t;
	int result;

	result = -EEXIST;
	spin_lock(&xprt_list_lock);
	list_for_each_entry(t, &xprt_list, list) {
		/* don't register the same transport class twice */
		if (t->ident == transport->ident)
			goto out;
	}

	list_add_tail(&transport->list, &xprt_list);
	printk(KERN_INFO "RPC: Registered %s transport module.\n",
	       transport->name);
	result = 0;

out:
	spin_unlock(&xprt_list_lock);
	return result;
}
EXPORT_SYMBOL_GPL(xprt_register_transport);

/**
 * xprt_unregister_transport - unregister a transport implementation
 * @transport: transport to unregister
 *
 * Returns:
 * 0:		transport successfully unregistered
 * -ENOENT:	transport never registered