fs/nfs/callback.c - linux - Git at Google

 /*
  * linux/fs/nfs/callback.c
  *
  * Copyright (C) 2004 Trond Myklebust
  *
  * NFSv4 callback handling
  */

 #include <linux/completion.h>
 #include <linux/ip.h>
 #include <linux/module.h>
 #include <linux/sunrpc/svc.h>
 #include <linux/sunrpc/svcsock.h>
 #include <linux/nfs_fs.h>
 #include <linux/mutex.h>
 #include <linux/freezer.h>
 #include <linux/kthread.h>
 #include <linux/sunrpc/svcauth_gss.h>
 #include <linux/sunrpc/bc_xprt.h>

 #include <net/inet_sock.h>

 #include "nfs4_fs.h"
 #include "callback.h"
 #include "internal.h"

 #define NFSDBG_FACILITY NFSDBG_CALLBACK

 struct nfs_callback_data {
 	unsigned int users;
 	struct svc_serv *serv;
 	struct svc_rqst *rqst;
 	struct task_struct *task;
 };

 static struct nfs_callback_data nfs_callback_info[NFS4_MAX_MINOR_VERSION + 1];
 static DEFINE_MUTEX(nfs_callback_mutex);
 static struct svc_program nfs4_callback_program;

 unsigned int nfs_callback_set_tcpport;
 unsigned short nfs_callback_tcpport;
 unsigned short nfs_callback_tcpport6;
 #define NFS_CALLBACK_MAXPORTNR (65535U)

 static int param_set_portnr(const char *val, const struct kernel_param *kp)
 {
 	unsigned long num;
 	int ret;

 	if (!val)
 		return -EINVAL;
 	ret = strict_strtoul(val, 0, &num);
 	if (ret == -EINVAL || num > NFS_CALLBACK_MAXPORTNR)
 		return -EINVAL;
 	*((unsigned int *)kp->arg) = num;
 	return 0;
 }
 static struct kernel_param_ops param_ops_portnr = {
 	.set = param_set_portnr,
 	.get = param_get_uint,
 };
 #define param_check_portnr(name, p) __param_check(name, p, unsigned int);

 module_param_named(callback_tcpport, nfs_callback_set_tcpport, portnr, 0644);

 /*
  * This is the NFSv4 callback kernel thread.
  */
 static int
 nfs4_callback_svc(void *vrqstp)
 {
 	int err, preverr = 0;
 	struct svc_rqst *rqstp = vrqstp;

 	set_freezable();

 	while (!kthread_should_stop()) {
 		/*
 		 * Listen for a request on the socket
 		 */
 		err = svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
 		if (err == -EAGAIN || err == -EINTR) {
 			preverr = err;
 			continue;
 		}
 		if (err < 0) {
 			if (err != preverr) {
 				printk(KERN_WARNING "NFS: %s: unexpected error "
 					"from svc_recv (%d)\n", __func__, err);
 				preverr = err;
 			}
 			schedule_timeout_uninterruptible(HZ);
 			continue;
 		}
 		preverr = err;
 		svc_process(rqstp);
 	}
 	return 0;
 }

 /*
  * Prepare to bring up the NFSv4 callback service
  */
 struct svc_rqst *
 nfs4_callback_up(struct svc_serv *serv, struct rpc_xprt *xprt)
 {
 	int ret;

 	ret = svc_create_xprt(serv, "tcp", xprt->xprt_net, PF_INET,
 				nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS);
 	if (ret <= 0)
 		goto out_err;
 	nfs_callback_tcpport = ret;
 	dprintk("NFS: Callback listener port = %u (af %u)\n",
 			nfs_callback_tcpport, PF_INET);

 	ret = svc_create_xprt(serv, "tcp", xprt->xprt_net, PF_INET6,
 				nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS);
 	if (ret > 0) {
 		nfs_callback_tcpport6 = ret;
 		dprintk("NFS: Callback listener port = %u (af %u)\n",
 				nfs_callback_tcpport6, PF_INET6);
 	} else if (ret == -EAFNOSUPPORT)
 		ret = 0;
 	else
 		goto out_err;

 	return svc_prepare_thread(serv, &serv->sv_pools[0], NUMA_NO_NODE);

 out_err:
 	if (ret == 0)
 		ret = -ENOMEM;
 	return ERR_PTR(ret);
 }

 #if defined(CONFIG_NFS_V4_1)
 /*
  * The callback service for NFSv4.1 callbacks
  */
 static int
 nfs41_callback_svc(void *vrqstp)
 {
 	struct svc_rqst *rqstp = vrqstp;
 	struct svc_serv *serv = rqstp->rq_server;
 	struct rpc_rqst *req;
 	int error;
 	DEFINE_WAIT(wq);

 	set_freezable();

 	while (!kthread_should_stop()) {
 		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
 		if (!list_empty(&serv->sv_cb_list)) {
 			req = list_first_entry(&serv->sv_cb_list,
 					struct rpc_rqst, rq_bc_list);
 			list_del(&req->rq_bc_list);
 			spin_unlock_bh(&serv->sv_cb_lock);
 			dprintk("Invoking bc_svc_process()\n");
 			error = bc_svc_process(serv, req, rqstp);
 			dprintk("bc_svc_process() returned w/ error code= %d\n",
 				error);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
 			schedule();
 		}
 		finish_wait(&serv->sv_cb_waitq, &wq);
 	}
 	return 0;
 }

 /*
  * Bring up the NFSv4.1 callback service
  */
 struct svc_rqst *
 nfs41_callback_up(struct svc_serv *serv, struct rpc_xprt *xprt)
 {
 	struct svc_rqst *rqstp;
 	int ret;

 	/*
 	 * Create an svc_sock for the back channel service that shares the
 	 * fore channel connection.
 	 * Returns the input port (0) and sets the svc_serv bc_xprt on success
 	 */
 	ret = svc_create_xprt(serv, "tcp-bc", xprt->xprt_net, PF_INET, 0,
 			      SVC_SOCK_ANONYMOUS);
 	if (ret < 0) {
 		rqstp = ERR_PTR(ret);
 		goto out;
 	}

 	/*
 	 * Save the svc_serv in the transport so that it can
 	 * be referenced when the session backchannel is initialized
 	 */
 	xprt->bc_serv = serv;

 	INIT_LIST_HEAD(&serv->sv_cb_list);
 	spin_lock_init(&serv->sv_cb_lock);
 	init_waitqueue_head(&serv->sv_cb_waitq);
 	rqstp = svc_prepare_thread(serv, &serv->sv_pools[0], NUMA_NO_NODE);
 	if (IS_ERR(rqstp)) {
 		svc_xprt_put(serv->sv_bc_xprt);
 		serv->sv_bc_xprt = NULL;
 	}
 out:
 	dprintk("--> %s return %ld\n", __func__,
 		IS_ERR(rqstp) ? PTR_ERR(rqstp) : 0);
 	return rqstp;
 }

 static inline int nfs_minorversion_callback_svc_setup(u32 minorversion,
 		struct svc_serv *serv, struct rpc_xprt *xprt,
 		struct svc_rqst **rqstpp, int (**callback_svc)(void *vrqstp))
 {
 	if (minorversion) {
 		*rqstpp = nfs41_callback_up(serv, xprt);
 		*callback_svc = nfs41_callback_svc;
 	}
 	return minorversion;
 }

 static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
 		struct nfs_callback_data *cb_info)
 {
 	if (minorversion)
 		xprt->bc_serv = cb_info->serv;
 }
 #else
 static inline int nfs_minorversion_callback_svc_setup(u32 minorversion,
 		struct svc_serv *serv, struct rpc_xprt *xprt,
 		struct svc_rqst **rqstpp, int (**callback_svc)(void *vrqstp))
 {
 	return 0;
 }

 static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
 		struct nfs_callback_data *cb_info)
 {
 }
 #endif /* CONFIG_NFS_V4_1 */

 /*
  * Bring up the callback thread if it is not already up.
  */
 int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
 {
 	struct svc_serv *serv = NULL;
 	struct svc_rqst *rqstp;
 	int (*callback_svc)(void *vrqstp);
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
 	char svc_name[12];
 	int ret = 0;
 	int minorversion_setup;

 	mutex_lock(&nfs_callback_mutex);
 	if (cb_info->users++ || cb_info->task != NULL) {
 		nfs_callback_bc_serv(minorversion, xprt, cb_info);
 		goto out;
 	}
 	serv = svc_create(&nfs4_callback_program, NFS4_CALLBACK_BUFSIZE, NULL);
 	if (!serv) {
 		ret = -ENOMEM;
 		goto out_err;
 	}

 	minorversion_setup =  nfs_minorversion_callback_svc_setup(minorversion,
 					serv, xprt, &rqstp, &callback_svc);
 	if (!minorversion_setup) {
 		/* v4.0 callback setup */
 		rqstp = nfs4_callback_up(serv, xprt);
 		callback_svc = nfs4_callback_svc;
 	}

 	if (IS_ERR(rqstp)) {
 		ret = PTR_ERR(rqstp);
 		goto out_err;
 	}

 	svc_sock_update_bufs(serv);

 	sprintf(svc_name, "nfsv4.%u-svc", minorversion);
 	cb_info->serv = serv;
 	cb_info->rqst = rqstp;
 	cb_info->task = kthread_run(callback_svc, cb_info->rqst, svc_name);
 	if (IS_ERR(cb_info->task)) {
 		ret = PTR_ERR(cb_info->task);
 		svc_exit_thread(cb_info->rqst);
 		cb_info->rqst = NULL;
 		cb_info->task = NULL;
 		goto out_err;
 	}
 out:
 	/*
 	 * svc_create creates the svc_serv with sv_nrthreads == 1, and then
 	 * svc_prepare_thread increments that. So we need to call svc_destroy
 	 * on both success and failure so that the refcount is 1 when the
 	 * thread exits.
 	 */
 	if (serv)
 		svc_destroy(serv);
 	mutex_unlock(&nfs_callback_mutex);
 	return ret;
 out_err:
 	dprintk("NFS: Couldn't create callback socket or server thread; "
 		"err = %d\n", ret);
 	cb_info->users--;
 	goto out;
 }

 /*
  * Kill the callback thread if it's no longer being used.
  */
 void nfs_callback_down(int minorversion)
 {
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];

 	mutex_lock(&nfs_callback_mutex);
 	cb_info->users--;
 	if (cb_info->users == 0 && cb_info->task != NULL) {
 		kthread_stop(cb_info->task);
 		svc_exit_thread(cb_info->rqst);
 		cb_info->serv = NULL;
 		cb_info->rqst = NULL;
 		cb_info->task = NULL;
 	}
 	mutex_unlock(&nfs_callback_mutex);
 }

 /* Boolean check of RPC_AUTH_GSS principal */
 int
 check_gss_callback_principal(struct nfs_client *clp, struct svc_rqst *rqstp)
 {
 	struct rpc_clnt *r = clp->cl_rpcclient;
 	char *p = svc_gss_principal(rqstp);

 	if (rqstp->rq_authop->flavour != RPC_AUTH_GSS)
 		return 1;

 	/* No RPC_AUTH_GSS on NFSv4.1 back channel yet */
 	if (clp->cl_minorversion != 0)
 		return 0;
 	/*
 	 * It might just be a normal user principal, in which case
 	 * userspace won't bother to tell us the name at all.
 	 */
 	if (p == NULL)
 		return 0;

 	/* Expect a GSS_C_NT_HOSTBASED_NAME like "nfs@serverhostname" */

 	if (memcmp(p, "nfs@", 4) != 0)
 		return 0;
 	p += 4;
 	if (strcmp(p, r->cl_server) != 0)
 		return 0;
 	return 1;
 }

 /*
  * pg_authenticate method for nfsv4 callback threads.
  *
  * The authflavor has been negotiated, so an incorrect flavor is a server
  * bug. Drop packets with incorrect authflavor.
  *
  * All other checking done after NFS decoding where the nfs_client can be
  * found in nfs4_callback_compound
  */
 static int nfs_callback_authenticate(struct svc_rqst *rqstp)
 {
 	switch (rqstp->rq_authop->flavour) {
 	case RPC_AUTH_NULL:
 		if (rqstp->rq_proc != CB_NULL)
 			return SVC_DROP;
 		break;
 	case RPC_AUTH_GSS:
 		/* No RPC_AUTH_GSS support yet in NFSv4.1 */
 		 if (svc_is_backchannel(rqstp))
 			return SVC_DROP;
 	}
 	return SVC_OK;
 }

 /*
  * Define NFS4 callback program
  */
 static struct svc_version *nfs4_callback_version[] = {
 	[1] = &nfs4_callback_version1,
 	[4] = &nfs4_callback_version4,
 };

 static struct svc_stat nfs4_callback_stats;

 static struct svc_program nfs4_callback_program = {
 	.pg_prog = NFS4_CALLBACK,			/* RPC service number */
 	.pg_nvers = ARRAY_SIZE(nfs4_callback_version),	/* Number of entries */
 	.pg_vers = nfs4_callback_version,		/* version table */
 	.pg_name = "NFSv4 callback",			/* service name */
 	.pg_class = "nfs",				/* authentication class */
 	.pg_stats = &nfs4_callback_stats,
 	.pg_authenticate = nfs_callback_authenticate,
 };
	/*
	* linux/fs/nfs/callback.c
	*
	* Copyright (C) 2004 Trond Myklebust
	*
	* NFSv4 callback handling
	*/

	#include <linux/completion.h>
	#include <linux/ip.h>
	#include <linux/module.h>
	#include <linux/sunrpc/svc.h>
	#include <linux/sunrpc/svcsock.h>
	#include <linux/nfs_fs.h>
	#include <linux/mutex.h>
	#include <linux/freezer.h>
	#include <linux/kthread.h>
	#include <linux/sunrpc/svcauth_gss.h>
	#include <linux/sunrpc/bc_xprt.h>

	#include <net/inet_sock.h>

	#include "nfs4_fs.h"
	#include "callback.h"
	#include "internal.h"

	#define NFSDBG_FACILITY NFSDBG_CALLBACK

	struct nfs_callback_data {
	unsigned int users;
	struct svc_serv *serv;
	struct svc_rqst *rqst;
	struct task_struct *task;
	};

	static struct nfs_callback_data nfs_callback_info[NFS4_MAX_MINOR_VERSION + 1];
	static DEFINE_MUTEX(nfs_callback_mutex);
	static struct svc_program nfs4_callback_program;

	unsigned int nfs_callback_set_tcpport;
	unsigned short nfs_callback_tcpport;
	unsigned short nfs_callback_tcpport6;
	#define NFS_CALLBACK_MAXPORTNR (65535U)

	static int param_set_portnr(const char val, const struct kernel_param kp)
	{
	unsigned long num;
	int ret;

	if (!val)
	return -EINVAL;
	ret = strict_strtoul(val, 0, &num);
	if (ret == -EINVAL \|\| num > NFS_CALLBACK_MAXPORTNR)
	return -EINVAL;
	((unsigned int )kp->arg) = num;
	return 0;
	}
	static struct kernel_param_ops param_ops_portnr = {
	.set = param_set_portnr,
	.get = param_get_uint,
	};
	#define param_check_portnr(name, p) __param_check(name, p, unsigned int);

	module_param_named(callback_tcpport, nfs_callback_set_tcpport, portnr, 0644);

	/*
	* This is the NFSv4 callback kernel thread.
	*/
	static int
	nfs4_callback_svc(void *vrqstp)
	{
	int err, preverr = 0;
	struct svc_rqst *rqstp = vrqstp;

	set_freezable();

	while (!kthread_should_stop()) {
	/*
	* Listen for a request on the socket
	*/
	err = svc_recv(rqstp, MAX_SCHEDULE_TIMEOUT);
	if (err == -EAGAIN \|\| err == -EINTR) {
	preverr = err;
	continue;
	}
	if (err < 0) {
	if (err != preverr) {
	printk(KERN_WARNING "NFS: %s: unexpected error "
	"from svc_recv (%d)\n", __func__, err);
	preverr = err;
	}
	schedule_timeout_uninterruptible(HZ);
	continue;
	}
	preverr = err;
	svc_process(rqstp);
	}
	return 0;
	}

	/*
	* Prepare to bring up the NFSv4 callback service
	*/
	struct svc_rqst *
	nfs4_callback_up(struct svc_serv serv, struct rpc_xprt xprt)
	{
	int ret;

	ret = svc_create_xprt(serv, "tcp", xprt->xprt_net, PF_INET,
	nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS);
	if (ret <= 0)
	goto out_err;
	nfs_callback_tcpport = ret;
	dprintk("NFS: Callback listener port = %u (af %u)\n",
	nfs_callback_tcpport, PF_INET);

	ret = svc_create_xprt(serv, "tcp", xprt->xprt_net, PF_INET6,
	nfs_callback_set_tcpport, SVC_SOCK_ANONYMOUS);
	if (ret > 0) {
	nfs_callback_tcpport6 = ret;
	dprintk("NFS: Callback listener port = %u (af %u)\n",
	nfs_callback_tcpport6, PF_INET6);
	} else if (ret == -EAFNOSUPPORT)
	ret = 0;
	else
	goto out_err;

	return svc_prepare_thread(serv, &serv->sv_pools[0], NUMA_NO_NODE);

	out_err:
	if (ret == 0)
	ret = -ENOMEM;
	return ERR_PTR(ret);
	}

	#if defined(CONFIG_NFS_V4_1)
	/*
	* The callback service for NFSv4.1 callbacks
	*/
	static int
	nfs41_callback_svc(void *vrqstp)
	{
	struct svc_rqst *rqstp = vrqstp;
	struct svc_serv *serv = rqstp->rq_server;
	struct rpc_rqst *req;
	int error;
	DEFINE_WAIT(wq);

	set_freezable();

	while (!kthread_should_stop()) {
	prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
	spin_lock_bh(&serv->sv_cb_lock);
	if (!list_empty(&serv->sv_cb_list)) {
	req = list_first_entry(&serv->sv_cb_list,
	struct rpc_rqst, rq_bc_list);
	list_del(&req->rq_bc_list);
	spin_unlock_bh(&serv->sv_cb_lock);
	dprintk("Invoking bc_svc_process()\n");
	error = bc_svc_process(serv, req, rqstp);
	dprintk("bc_svc_process() returned w/ error code= %d\n",
	error);
	} else {
	spin_unlock_bh(&serv->sv_cb_lock);
	schedule();
	}
	finish_wait(&serv->sv_cb_waitq, &wq);
	}
	return 0;
	}

	/*
	* Bring up the NFSv4.1 callback service
	*/
	struct svc_rqst *
	nfs41_callback_up(struct svc_serv serv, struct rpc_xprt xprt)
	{
	struct svc_rqst *rqstp;
	int ret;

	/*
	* Create an svc_sock for the back channel service that shares the
	* fore channel connection.
	* Returns the input port (0) and sets the svc_serv bc_xprt on success
	*/
	ret = svc_create_xprt(serv, "tcp-bc", xprt->xprt_net, PF_INET, 0,
	SVC_SOCK_ANONYMOUS);
	if (ret < 0) {
	rqstp = ERR_PTR(ret);
	goto out;
	}

	/*
	* Save the svc_serv in the transport so that it can
	* be referenced when the session backchannel is initialized
	*/
	xprt->bc_serv = serv;

	INIT_LIST_HEAD(&serv->sv_cb_list);
	spin_lock_init(&serv->sv_cb_lock);
	init_waitqueue_head(&serv->sv_cb_waitq);
	rqstp = svc_prepare_thread(serv, &serv->sv_pools[0], NUMA_NO_NODE);
	if (IS_ERR(rqstp)) {
	svc_xprt_put(serv->sv_bc_xprt);
	serv->sv_bc_xprt = NULL;
	}
	out:
	dprintk("--> %s return %ld\n", __func__,
	IS_ERR(rqstp) ? PTR_ERR(rqstp) : 0);
	return rqstp;
	}

	static inline int nfs_minorversion_callback_svc_setup(u32 minorversion,
	struct svc_serv serv, struct rpc_xprt xprt,
	struct svc_rqst rqstpp, int (callback_svc)(void *vrqstp))
	{
	if (minorversion) {
	*rqstpp = nfs41_callback_up(serv, xprt);
	*callback_svc = nfs41_callback_svc;
	}
	return minorversion;
	}

	static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
	struct nfs_callback_data *cb_info)
	{
	if (minorversion)
	xprt->bc_serv = cb_info->serv;
	}
	#else
	static inline int nfs_minorversion_callback_svc_setup(u32 minorversion,
	struct svc_serv serv, struct rpc_xprt xprt,
	struct svc_rqst rqstpp, int (callback_svc)(void *vrqstp))
	{
	return 0;
	}

	static inline void nfs_callback_bc_serv(u32 minorversion, struct rpc_xprt *xprt,
	struct nfs_callback_data *cb_info)
	{
	}
	#endif /* CONFIG_NFS_V4_1 */

	/*
	* Bring up the callback thread if it is not already up.
	*/
	int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
	{
	struct svc_serv *serv = NULL;
	struct svc_rqst *rqstp;
	int (callback_svc)(void vrqstp);
	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
	char svc_name[12];
	int ret = 0;
	int minorversion_setup;

	mutex_lock(&nfs_callback_mutex);
	if (cb_info->users++ \|\| cb_info->task != NULL) {
	nfs_callback_bc_serv(minorversion, xprt, cb_info);
	goto out;
	}
	serv = svc_create(&nfs4_callback_program, NFS4_CALLBACK_BUFSIZE, NULL);
	if (!serv) {
	ret = -ENOMEM;
	goto out_err;
	}

	minorversion_setup = nfs_minorversion_callback_svc_setup(minorversion,
	serv, xprt, &rqstp, &callback_svc);
	if (!minorversion_setup) {
	/* v4.0 callback setup */
	rqstp = nfs4_callback_up(serv, xprt);
	callback_svc = nfs4_callback_svc;
	}

	if (IS_ERR(rqstp)) {
	ret = PTR_ERR(rqstp);
	goto out_err;
	}

	svc_sock_update_bufs(serv);

	sprintf(svc_name, "nfsv4.%u-svc", minorversion);
	cb_info->serv = serv;
	cb_info->rqst = rqstp;
	cb_info->task = kthread_run(callback_svc, cb_info->rqst, svc_name);
	if (IS_ERR(cb_info->task)) {
	ret = PTR_ERR(cb_info->task);
	svc_exit_thread(cb_info->rqst);
	cb_info->rqst = NULL;
	cb_info->task = NULL;
	goto out_err;
	}
	out:
	/*
	* svc_create creates the svc_serv with sv_nrthreads == 1, and then
	* svc_prepare_thread increments that. So we need to call svc_destroy
	* on both success and failure so that the refcount is 1 when the
	* thread exits.
	*/
	if (serv)
	svc_destroy(serv);
	mutex_unlock(&nfs_callback_mutex);
	return ret;
	out_err:
	dprintk("NFS: Couldn't create callback socket or server thread; "
	"err = %d\n", ret);
	cb_info->users--;
	goto out;
	}

	/*
	* Kill the callback thread if it's no longer being used.
	*/
	void nfs_callback_down(int minorversion)
	{
	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];

	mutex_lock(&nfs_callback_mutex);
	cb_info->users--;
	if (cb_info->users == 0 && cb_info->task != NULL) {
	kthread_stop(cb_info->task);
	svc_exit_thread(cb_info->rqst);
	cb_info->serv = NULL;
	cb_info->rqst = NULL;
	cb_info->task = NULL;
	}
	mutex_unlock(&nfs_callback_mutex);
	}

	/* Boolean check of RPC_AUTH_GSS principal */
	int
	check_gss_callback_principal(struct nfs_client clp, struct svc_rqst rqstp)
	{
	struct rpc_clnt *r = clp->cl_rpcclient;
	char *p = svc_gss_principal(rqstp);

	if (rqstp->rq_authop->flavour != RPC_AUTH_GSS)
	return 1;

	/* No RPC_AUTH_GSS on NFSv4.1 back channel yet */
	if (clp->cl_minorversion != 0)
	return 0;
	/*
	* It might just be a normal user principal, in which case
	* userspace won't bother to tell us the name at all.
	*/
	if (p == NULL)
	return 0;

	/* Expect a GSS_C_NT_HOSTBASED_NAME like "nfs@serverhostname" */

	if (memcmp(p, "nfs@", 4) != 0)
	return 0;
	p += 4;
	if (strcmp(p, r->cl_server) != 0)
	return 0;
	return 1;
	}

	/*
	* pg_authenticate method for nfsv4 callback threads.
	*
	* The authflavor has been negotiated, so an incorrect flavor is a server
	* bug. Drop packets with incorrect authflavor.
	*
	* All other checking done after NFS decoding where the nfs_client can be
	* found in nfs4_callback_compound
	*/
	static int nfs_callback_authenticate(struct svc_rqst *rqstp)
	{
	switch (rqstp->rq_authop->flavour) {
	case RPC_AUTH_NULL:
	if (rqstp->rq_proc != CB_NULL)
	return SVC_DROP;
	break;
	case RPC_AUTH_GSS:
	/* No RPC_AUTH_GSS support yet in NFSv4.1 */
	if (svc_is_backchannel(rqstp))
	return SVC_DROP;
	}
	return SVC_OK;
	}

	/*
	* Define NFS4 callback program
	*/
	static struct svc_version *nfs4_callback_version[] = {
	[1] = &nfs4_callback_version1,
	[4] = &nfs4_callback_version4,
	};

	static struct svc_stat nfs4_callback_stats;

	static struct svc_program nfs4_callback_program = {
	.pg_prog = NFS4_CALLBACK, /* RPC service number */
	.pg_nvers = ARRAY_SIZE(nfs4_callback_version), /* Number of entries */
	.pg_vers = nfs4_callback_version, /* version table */
	.pg_name = "NFSv4 callback", /* service name */
	.pg_class = "nfs", /* authentication class */
	.pg_stats = &nfs4_callback_stats,
	.pg_authenticate = nfs_callback_authenticate,
	};