/*

   *  Copyright (c) 2001 The Regents of the University of Michigan.
   *  All rights reserved.
   *
   *  Kendrick Smith <kmsmith@umich.edu>
   *  Andy Adamson <andros@umich.edu>
   *
   *  Redistribution and use in source and binary forms, with or without
   *  modification, are permitted provided that the following conditions
   *  are met:
   *
   *  1. Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   *  2. Redistributions in binary form must reproduce the above copyright
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   *  3. Neither the name of the University nor the names of its
   *     contributors may be used to endorse or promote products derived
   *     from this software without specific prior written permission.
   *
   *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
   *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   *  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   *  DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   *  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
   *  BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */

  #include <linux/sunrpc/clnt.h>

  #include <linux/sunrpc/svc_xprt.h>

  #include <linux/slab.h>

  #include "nfsd.h"
  #include "state.h"

  
  #define NFSDDBG_FACILITY                NFSDDBG_PROC
  
  #define NFSPROC4_CB_NULL 0
  #define NFSPROC4_CB_COMPOUND 1

  /* Index of predefined Linux callback client operations */
  
  enum {

  	NFSPROC4_CLNT_CB_NULL = 0,

  	NFSPROC4_CLNT_CB_RECALL,

  	NFSPROC4_CLNT_CB_SEQUENCE,

  };

  #define NFS4_MAXTAGLEN		20
  
  #define NFS4_enc_cb_null_sz		0
  #define NFS4_dec_cb_null_sz		0
  #define cb_compound_enc_hdr_sz		4
  #define cb_compound_dec_hdr_sz		(3 + (NFS4_MAXTAGLEN >> 2))

  #define sessionid_sz			(NFS4_MAX_SESSIONID_LEN >> 2)
  #define cb_sequence_enc_sz		(sessionid_sz + 4 +             \
  					1 /* no referring calls list yet */)
  #define cb_sequence_dec_sz		(op_dec_sz + sessionid_sz + 4)

  #define op_enc_sz			1
  #define op_dec_sz			2
  #define enc_nfs4_fh_sz			(1 + (NFS4_FHSIZE >> 2))

  #define enc_stateid_sz			(NFS4_STATEID_SIZE >> 2)

  #define NFS4_enc_cb_recall_sz		(cb_compound_enc_hdr_sz +       \

  					cb_sequence_enc_sz +            \

  					1 + enc_stateid_sz +            \
  					enc_nfs4_fh_sz)
  
  #define NFS4_dec_cb_recall_sz		(cb_compound_dec_hdr_sz  +      \

  					cb_sequence_dec_sz +            \

  					op_dec_sz)

  struct nfs4_cb_compound_hdr {

  	/* args */
  	u32		ident;	/* minorversion 0 only */

  	u32		nops;

  	__be32		*nops_p;

  	u32		minorversion;

  	/* res */
  	int		status;

  };

  /*
   * Handle decode buffer overflows out-of-line.
   */
  static void print_overflow_msg(const char *func, const struct xdr_stream *xdr)

  {

  	dprintk("NFS: %s prematurely hit the end of our receive buffer. "
  		"Remaining buffer length is %tu words.
  ",
  		func, xdr->end - xdr->p);

  }

  static __be32 *xdr_encode_empty_array(__be32 *p)
  {
  	*p++ = xdr_zero;
  	return p;
  }
  
  /*
   * Encode/decode NFSv4 CB basic data types
   *
   * Basic NFSv4 callback data types are defined in section 15 of RFC
   * 3530: "Network File System (NFS) version 4 Protocol" and section
   * 20 of RFC 5661: "Network File System (NFS) Version 4 Minor Version
   * 1 Protocol"
   */
  
  /*
   *	nfs_cb_opnum4
   *
   *	enum nfs_cb_opnum4 {
   *		OP_CB_GETATTR		= 3,
   *		  ...
   *	};
   */
  enum nfs_cb_opnum4 {
  	OP_CB_GETATTR			= 3,
  	OP_CB_RECALL			= 4,
  	OP_CB_LAYOUTRECALL		= 5,
  	OP_CB_NOTIFY			= 6,
  	OP_CB_PUSH_DELEG		= 7,
  	OP_CB_RECALL_ANY		= 8,
  	OP_CB_RECALLABLE_OBJ_AVAIL	= 9,
  	OP_CB_RECALL_SLOT		= 10,
  	OP_CB_SEQUENCE			= 11,
  	OP_CB_WANTS_CANCELLED		= 12,
  	OP_CB_NOTIFY_LOCK		= 13,
  	OP_CB_NOTIFY_DEVICEID		= 14,
  	OP_CB_ILLEGAL			= 10044
  };
  
  static void encode_nfs_cb_opnum4(struct xdr_stream *xdr, enum nfs_cb_opnum4 op)
  {
  	__be32 *p;
  
  	p = xdr_reserve_space(xdr, 4);
  	*p = cpu_to_be32(op);
  }
  
  /*
   * nfs_fh4
   *
   *	typedef opaque nfs_fh4<NFS4_FHSIZE>;
   */
  static void encode_nfs_fh4(struct xdr_stream *xdr, const struct knfsd_fh *fh)
  {
  	u32 length = fh->fh_size;
  	__be32 *p;
  
  	BUG_ON(length > NFS4_FHSIZE);
  	p = xdr_reserve_space(xdr, 4 + length);
  	xdr_encode_opaque(p, &fh->fh_base, length);
  }

  /*

   * stateid4
   *
   *	struct stateid4 {
   *		uint32_t	seqid;
   *		opaque		other[12];
   *	};

   */

  static void encode_stateid4(struct xdr_stream *xdr, const stateid_t *sid)
  {
  	__be32 *p;

  	p = xdr_reserve_space(xdr, NFS4_STATEID_SIZE);
  	*p++ = cpu_to_be32(sid->si_generation);
  	xdr_encode_opaque_fixed(p, &sid->si_opaque, NFS4_STATEID_OTHER_SIZE);
  }
  
  /*
   * sessionid4
   *
   *	typedef opaque sessionid4[NFS4_SESSIONID_SIZE];
   */
  static void encode_sessionid4(struct xdr_stream *xdr,
  			      const struct nfsd4_session *session)

  {
  	__be32 *p;

  	p = xdr_reserve_space(xdr, NFS4_MAX_SESSIONID_LEN);
  	xdr_encode_opaque_fixed(p, session->se_sessionid.data,
  					NFS4_MAX_SESSIONID_LEN);

  }

  /*

   * nfsstat4
   */
  static const struct {
  	int stat;
  	int errno;
  } nfs_cb_errtbl[] = {
  	{ NFS4_OK,		0		},
  	{ NFS4ERR_PERM,		-EPERM		},
  	{ NFS4ERR_NOENT,	-ENOENT		},
  	{ NFS4ERR_IO,		-EIO		},
  	{ NFS4ERR_NXIO,		-ENXIO		},
  	{ NFS4ERR_ACCESS,	-EACCES		},
  	{ NFS4ERR_EXIST,	-EEXIST		},
  	{ NFS4ERR_XDEV,		-EXDEV		},
  	{ NFS4ERR_NOTDIR,	-ENOTDIR	},
  	{ NFS4ERR_ISDIR,	-EISDIR		},
  	{ NFS4ERR_INVAL,	-EINVAL		},
  	{ NFS4ERR_FBIG,		-EFBIG		},
  	{ NFS4ERR_NOSPC,	-ENOSPC		},
  	{ NFS4ERR_ROFS,		-EROFS		},
  	{ NFS4ERR_MLINK,	-EMLINK		},
  	{ NFS4ERR_NAMETOOLONG,	-ENAMETOOLONG	},
  	{ NFS4ERR_NOTEMPTY,	-ENOTEMPTY	},
  	{ NFS4ERR_DQUOT,	-EDQUOT		},
  	{ NFS4ERR_STALE,	-ESTALE		},
  	{ NFS4ERR_BADHANDLE,	-EBADHANDLE	},
  	{ NFS4ERR_BAD_COOKIE,	-EBADCOOKIE	},
  	{ NFS4ERR_NOTSUPP,	-ENOTSUPP	},
  	{ NFS4ERR_TOOSMALL,	-ETOOSMALL	},
  	{ NFS4ERR_SERVERFAULT,	-ESERVERFAULT	},
  	{ NFS4ERR_BADTYPE,	-EBADTYPE	},
  	{ NFS4ERR_LOCKED,	-EAGAIN		},
  	{ NFS4ERR_RESOURCE,	-EREMOTEIO	},
  	{ NFS4ERR_SYMLINK,	-ELOOP		},
  	{ NFS4ERR_OP_ILLEGAL,	-EOPNOTSUPP	},
  	{ NFS4ERR_DEADLOCK,	-EDEADLK	},
  	{ -1,			-EIO		}
  };
  
  /*
   * If we cannot translate the error, the recovery routines should
   * handle it.
   *
   * Note: remaining NFSv4 error codes have values > 10000, so should
   * not conflict with native Linux error codes.
   */
  static int nfs_cb_stat_to_errno(int status)
  {
  	int i;
  
  	for (i = 0; nfs_cb_errtbl[i].stat != -1; i++) {
  		if (nfs_cb_errtbl[i].stat == status)
  			return nfs_cb_errtbl[i].errno;
  	}
  
  	dprintk("NFSD: Unrecognized NFS CB status value: %u
  ", status);
  	return -status;
  }
  
  static int decode_cb_op_status(struct xdr_stream *xdr, enum nfs_opnum4 expected,
  			       enum nfsstat4 *status)
  {
  	__be32 *p;
  	u32 op;
  
  	p = xdr_inline_decode(xdr, 4 + 4);
  	if (unlikely(p == NULL))
  		goto out_overflow;
  	op = be32_to_cpup(p++);
  	if (unlikely(op != expected))
  		goto out_unexpected;
  	*status = be32_to_cpup(p);
  	return 0;
  out_overflow:
  	print_overflow_msg(__func__, xdr);
  	return -EIO;
  out_unexpected:
  	dprintk("NFSD: Callback server returned operation %d but "
  		"we issued a request for %d
  ", op, expected);
  	return -EIO;
  }
  
  /*

   * CB_COMPOUND4args
   *
   *	struct CB_COMPOUND4args {
   *		utf8str_cs	tag;
   *		uint32_t	minorversion;
   *		uint32_t	callback_ident;
   *		nfs_cb_argop4	argarray<>;
   *	};
  */
  static void encode_cb_compound4args(struct xdr_stream *xdr,
  				    struct nfs4_cb_compound_hdr *hdr)

  {

  	__be32 * p;

  	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4);
  	p = xdr_encode_empty_array(p);		/* empty tag */
  	*p++ = cpu_to_be32(hdr->minorversion);
  	*p++ = cpu_to_be32(hdr->ident);

  	hdr->nops_p = p;

  	*p = cpu_to_be32(hdr->nops);		/* argarray element count */

  }

  /*
   * Update argarray element count
   */

  static void encode_cb_nops(struct nfs4_cb_compound_hdr *hdr)
  {

  	BUG_ON(hdr->nops > NFS4_MAX_BACK_CHANNEL_OPS);
  	*hdr->nops_p = cpu_to_be32(hdr->nops);

  }

  /*

   * CB_COMPOUND4res
   *
   *	struct CB_COMPOUND4res {
   *		nfsstat4	status;
   *		utf8str_cs	tag;
   *		nfs_cb_resop4	resarray<>;
   *	};
   */
  static int decode_cb_compound4res(struct xdr_stream *xdr,
  				  struct nfs4_cb_compound_hdr *hdr)
  {
  	u32 length;
  	__be32 *p;
  
  	p = xdr_inline_decode(xdr, 4 + 4);
  	if (unlikely(p == NULL))
  		goto out_overflow;
  	hdr->status = be32_to_cpup(p++);
  	/* Ignore the tag */
  	length = be32_to_cpup(p++);
  	p = xdr_inline_decode(xdr, length + 4);
  	if (unlikely(p == NULL))
  		goto out_overflow;
  	hdr->nops = be32_to_cpup(p);
  	return 0;
  out_overflow:
  	print_overflow_msg(__func__, xdr);
  	return -EIO;
  }
  
  /*

   * CB_RECALL4args
   *
   *	struct CB_RECALL4args {
   *		stateid4	stateid;
   *		bool		truncate;
   *		nfs_fh4		fh;
   *	};
   */
  static void encode_cb_recall4args(struct xdr_stream *xdr,
  				  const struct nfs4_delegation *dp,
  				  struct nfs4_cb_compound_hdr *hdr)

  {

  	__be32 *p;

  
  	encode_nfs_cb_opnum4(xdr, OP_CB_RECALL);
  	encode_stateid4(xdr, &dp->dl_stateid);
  
  	p = xdr_reserve_space(xdr, 4);
  	*p++ = xdr_zero;			/* truncate */
  
  	encode_nfs_fh4(xdr, &dp->dl_fh);

  	hdr->nops++;

  }

  /*
   * CB_SEQUENCE4args
   *
   *	struct CB_SEQUENCE4args {
   *		sessionid4		csa_sessionid;
   *		sequenceid4		csa_sequenceid;
   *		slotid4			csa_slotid;
   *		slotid4			csa_highest_slotid;
   *		bool			csa_cachethis;
   *		referring_call_list4	csa_referring_call_lists<>;
   *	};
   */
  static void encode_cb_sequence4args(struct xdr_stream *xdr,
  				    const struct nfsd4_callback *cb,
  				    struct nfs4_cb_compound_hdr *hdr)

  {

  	struct nfsd4_session *session = cb->cb_clp->cl_cb_session;

  	__be32 *p;
  
  	if (hdr->minorversion == 0)
  		return;

  	encode_nfs_cb_opnum4(xdr, OP_CB_SEQUENCE);
  	encode_sessionid4(xdr, session);
  
  	p = xdr_reserve_space(xdr, 4 + 4 + 4 + 4 + 4);
  	*p++ = cpu_to_be32(session->se_cb_seq_nr);	/* csa_sequenceid */
  	*p++ = xdr_zero;			/* csa_slotid */
  	*p++ = xdr_zero;			/* csa_highest_slotid */
  	*p++ = xdr_zero;			/* csa_cachethis */
  	xdr_encode_empty_array(p);		/* csa_referring_call_lists */

  	hdr->nops++;
  }

  /*

   * CB_SEQUENCE4resok
   *
   *	struct CB_SEQUENCE4resok {
   *		sessionid4	csr_sessionid;
   *		sequenceid4	csr_sequenceid;
   *		slotid4		csr_slotid;
   *		slotid4		csr_highest_slotid;
   *		slotid4		csr_target_highest_slotid;
   *	};
   *
   *	union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
   *	case NFS4_OK:
   *		CB_SEQUENCE4resok	csr_resok4;
   *	default:
   *		void;
   *	};
   *
   * Our current back channel implmentation supports a single backchannel
   * with a single slot.
   */
  static int decode_cb_sequence4resok(struct xdr_stream *xdr,
  				    struct nfsd4_callback *cb)
  {
  	struct nfsd4_session *session = cb->cb_clp->cl_cb_session;
  	struct nfs4_sessionid id;
  	int status;
  	__be32 *p;
  	u32 dummy;
  
  	status = -ESERVERFAULT;
  
  	/*
  	 * If the server returns different values for sessionID, slotID or
  	 * sequence number, the server is looney tunes.
  	 */

  	p = xdr_inline_decode(xdr, NFS4_MAX_SESSIONID_LEN + 4 + 4 + 4 + 4);

  	if (unlikely(p == NULL))
  		goto out_overflow;
  	memcpy(id.data, p, NFS4_MAX_SESSIONID_LEN);
  	if (memcmp(id.data, session->se_sessionid.data,
  					NFS4_MAX_SESSIONID_LEN) != 0) {
  		dprintk("NFS: %s Invalid session id
  ", __func__);
  		goto out;
  	}
  	p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN);
  
  	dummy = be32_to_cpup(p++);
  	if (dummy != session->se_cb_seq_nr) {
  		dprintk("NFS: %s Invalid sequence number
  ", __func__);
  		goto out;
  	}
  
  	dummy = be32_to_cpup(p++);
  	if (dummy != 0) {
  		dprintk("NFS: %s Invalid slotid
  ", __func__);
  		goto out;
  	}
  
  	/*
  	 * FIXME: process highest slotid and target highest slotid
  	 */
  	status = 0;
  out:
  	return status;
  out_overflow:
  	print_overflow_msg(__func__, xdr);
  	return -EIO;
  }
  
  static int decode_cb_sequence4res(struct xdr_stream *xdr,
  				  struct nfsd4_callback *cb)
  {
  	enum nfsstat4 nfserr;
  	int status;
  
  	if (cb->cb_minorversion == 0)
  		return 0;
  
  	status = decode_cb_op_status(xdr, OP_CB_SEQUENCE, &nfserr);
  	if (unlikely(status))
  		goto out;
  	if (unlikely(nfserr != NFS4_OK))
  		goto out_default;
  	status = decode_cb_sequence4resok(xdr, cb);
  out:
  	return status;
  out_default:

  	return nfs_cb_stat_to_errno(nfserr);

  }
  
  /*

   * NFSv4.0 and NFSv4.1 XDR encode functions
   *
   * NFSv4.0 callback argument types are defined in section 15 of RFC
   * 3530: "Network File System (NFS) version 4 Protocol" and section 20
   * of RFC 5661:  "Network File System (NFS) Version 4 Minor Version 1
   * Protocol".
   */
  
  /*
   * NB: Without this zero space reservation, callbacks over krb5p fail
   */

  static void nfs4_xdr_enc_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
  				 void *__unused)

  {

  	xdr_reserve_space(xdr, 0);

  }

  /*
   * 20.2. Operation 4: CB_RECALL - Recall a Delegation
   */

  static void nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, struct xdr_stream *xdr,
  				   const struct nfsd4_callback *cb)

  {

  	const struct nfs4_delegation *args = cb->cb_op;

  	struct nfs4_cb_compound_hdr hdr = {

  		.ident = cb->cb_clp->cl_cb_ident,

  		.minorversion = cb->cb_minorversion,

  	};

  	encode_cb_compound4args(xdr, &hdr);
  	encode_cb_sequence4args(xdr, cb, &hdr);
  	encode_cb_recall4args(xdr, args, &hdr);

  	encode_cb_nops(&hdr);

  }

  /*

   * NFSv4.0 and NFSv4.1 XDR decode functions
   *
   * NFSv4.0 callback result types are defined in section 15 of RFC
   * 3530: "Network File System (NFS) version 4 Protocol" and section 20
   * of RFC 5661:  "Network File System (NFS) Version 4 Minor Version 1
   * Protocol".

   */

  static int nfs4_xdr_dec_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
  				void *__unused)

  {
  	return 0;
  }

  /*
   * 20.2. Operation 4: CB_RECALL - Recall a Delegation
   */

  static int nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp,
  				  struct xdr_stream *xdr,

  				  struct nfsd4_callback *cb)

  {

  	struct nfs4_cb_compound_hdr hdr;

  	enum nfsstat4 nfserr;

  	int status;

  	status = decode_cb_compound4res(xdr, &hdr);

  	if (unlikely(status))

  		goto out;

  
  	if (cb != NULL) {

  		status = decode_cb_sequence4res(xdr, cb);

  		if (unlikely(status))

  			goto out;
  	}

  	status = decode_cb_op_status(xdr, OP_CB_RECALL, &nfserr);

  	if (unlikely(status))
  		goto out;
  	if (unlikely(nfserr != NFS4_OK))

  		status = nfs_cb_stat_to_errno(nfserr);

  out:
  	return status;
  }
  
  /*
   * RPC procedure tables
   */

  #define PROC(proc, call, argtype, restype)				\
  [NFSPROC4_CLNT_##proc] = {						\
  	.p_proc    = NFSPROC4_CB_##call,				\

  	.p_encode  = (kxdreproc_t)nfs4_xdr_enc_##argtype,		\

  	.p_decode  = (kxdrdproc_t)nfs4_xdr_dec_##restype,		\

  	.p_arglen  = NFS4_enc_##argtype##_sz,				\
  	.p_replen  = NFS4_dec_##restype##_sz,				\
  	.p_statidx = NFSPROC4_CB_##call,				\
  	.p_name    = #proc,						\

  }

  static struct rpc_procinfo nfs4_cb_procedures[] = {
  	PROC(CB_NULL,	NULL,		cb_null,	cb_null),
  	PROC(CB_RECALL,	COMPOUND,	cb_recall,	cb_recall),

  };

  static struct rpc_version nfs_cb_version4 = {

  /*
   * Note on the callback rpc program version number: despite language in rfc
   * 5661 section 18.36.3 requiring servers to use 4 in this field, the
   * official xdr descriptions for both 4.0 and 4.1 specify version 1, and
   * in practice that appears to be what implementations use.  The section
   * 18.36.3 language is expected to be fixed in an erratum.
   */

  	.number			= 1,
  	.nrprocs		= ARRAY_SIZE(nfs4_cb_procedures),
  	.procs			= nfs4_cb_procedures

  };

  static struct rpc_version *nfs_cb_version[] = {

  	&nfs_cb_version4,
  };

  static struct rpc_program cb_program;
  
  static struct rpc_stat cb_stats = {

  	.program		= &cb_program

  };
  
  #define NFS4_CALLBACK 0x40000000
  static struct rpc_program cb_program = {

  	.name			= "nfs4_cb",
  	.number			= NFS4_CALLBACK,
  	.nrvers			= ARRAY_SIZE(nfs_cb_version),
  	.version		= nfs_cb_version,
  	.stats			= &cb_stats,
  	.pipe_dir_name		= "/nfsd4_cb",

  };

  static int max_cb_time(void)
  {

  	return max(nfsd4_lease/10, (time_t)1) * HZ;

  }

  static int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *conn, struct nfsd4_session *ses)

  {

  	struct rpc_timeout	timeparms = {

  		.to_initval	= max_cb_time(),
  		.to_retries	= 0,

  	};

  	struct rpc_create_args args = {

  		.net		= &init_net,

  		.address	= (struct sockaddr *) &conn->cb_addr,
  		.addrsize	= conn->cb_addrlen,

  		.saddress	= (struct sockaddr *) &conn->cb_saddr,

  		.timeout	= &timeparms,

  		.program	= &cb_program,

  		.version	= 0,

  		.authflavor	= clp->cl_flavor,

  		.flags		= (RPC_CLNT_CREATE_NOPING | RPC_CLNT_CREATE_QUIET),

  	};

  	struct rpc_clnt *client;

  	if (clp->cl_minorversion == 0) {
  		if (!clp->cl_principal && (clp->cl_flavor >= RPC_AUTH_GSS_KRB5))
  			return -EINVAL;
  		args.client_name = clp->cl_principal;
  		args.prognumber	= conn->cb_prog,
  		args.protocol = XPRT_TRANSPORT_TCP;
  		clp->cl_cb_ident = conn->cb_ident;
  	} else {

  		if (!conn->cb_xprt)
  			return -EINVAL;
  		clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
  		clp->cl_cb_session = ses;

  		args.bc_xprt = conn->cb_xprt;

  		args.prognumber = clp->cl_cb_session->se_cb_prog;

  		args.protocol = XPRT_TRANSPORT_BC_TCP;
  	}

  	/* Create RPC client */

  	client = rpc_create(&args);

  	if (IS_ERR(client)) {

  		dprintk("NFSD: couldn't create callback client: %ld
  ",
  			PTR_ERR(client));

  		return PTR_ERR(client);
  	}

  	clp->cl_cb_client = client;

  	return 0;

  
  }

  static void warn_no_callback_path(struct nfs4_client *clp, int reason)
  {
  	dprintk("NFSD: warning: no callback path to client %.*s: error %d
  ",
  		(int)clp->cl_name.len, clp->cl_name.data, reason);
  }

  static void nfsd4_mark_cb_down(struct nfs4_client *clp, int reason)
  {
  	clp->cl_cb_state = NFSD4_CB_DOWN;
  	warn_no_callback_path(clp, reason);
  }

  static void nfsd4_cb_probe_done(struct rpc_task *task, void *calldata)
  {

  	struct nfs4_client *clp = container_of(calldata, struct nfs4_client, cl_cb_null);

  
  	if (task->tk_status)

  		nfsd4_mark_cb_down(clp, task->tk_status);

  	else

  		clp->cl_cb_state = NFSD4_CB_UP;

  }
  
  static const struct rpc_call_ops nfsd4_cb_probe_ops = {

  	/* XXX: release method to ensure we set the cb channel down if
  	 * necessary on early failure? */

  	.rpc_call_done = nfsd4_cb_probe_done,
  };

  static struct rpc_cred *callback_cred;
  
  int set_callback_cred(void)

  {

  	if (callback_cred)
  		return 0;

  	callback_cred = rpc_lookup_machine_cred();
  	if (!callback_cred)
  		return -ENOMEM;
  	return 0;

  }

  static struct workqueue_struct *callback_wq;

  static void run_nfsd4_cb(struct nfsd4_callback *cb)
  {
  	queue_work(callback_wq, &cb->cb_work);
  }

  static void do_probe_callback(struct nfs4_client *clp)

  {

  	struct nfsd4_callback *cb = &clp->cl_cb_null;

  	cb->cb_op = NULL;
  	cb->cb_clp = clp;

  
  	cb->cb_msg.rpc_proc = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_NULL];
  	cb->cb_msg.rpc_argp = NULL;
  	cb->cb_msg.rpc_resp = NULL;
  	cb->cb_msg.rpc_cred = callback_cred;
  
  	cb->cb_ops = &nfsd4_cb_probe_ops;

  	run_nfsd4_cb(cb);

  }
  
  /*

   * Poke the callback thread to process any updates to the callback
   * parameters, and send a null probe.

   */

  void nfsd4_probe_callback(struct nfs4_client *clp)
  {

  	/* XXX: atomicity?  Also, should we be using cl_cb_flags? */
  	clp->cl_cb_state = NFSD4_CB_UNKNOWN;

  	set_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
  	do_probe_callback(clp);
  }

  void nfsd4_probe_callback_sync(struct nfs4_client *clp)

  {

  	nfsd4_probe_callback(clp);
  	flush_workqueue(callback_wq);
  }

  void nfsd4_change_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)

  {

  	clp->cl_cb_state = NFSD4_CB_UNKNOWN;

  	spin_lock(&clp->cl_lock);
  	memcpy(&clp->cl_cb_conn, conn, sizeof(struct nfs4_cb_conn));

  	spin_unlock(&clp->cl_lock);

  }

  /*
   * There's currently a single callback channel slot.
   * If the slot is available, then mark it busy.  Otherwise, set the
   * thread for sleeping on the callback RPC wait queue.
   */

  static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct rpc_task *task)

  {

  	if (test_and_set_bit(0, &clp->cl_cb_slot_busy) != 0) {
  		rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
  		dprintk("%s slot is busy
  ", __func__);

  		return false;

  	}

  	return true;

  }
  
  /*
   * TODO: cb_sequence should support referring call lists, cachethis, multiple
   * slots, and mark callback channel down on communication errors.
   */
  static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
  {

  	struct nfsd4_callback *cb = calldata;
  	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);

  	struct nfs4_client *clp = dp->dl_client;

  	u32 minorversion = clp->cl_minorversion;

  	cb->cb_minorversion = minorversion;

  	if (minorversion) {

  		if (!nfsd41_cb_get_slot(clp, task))

  			return;

  	}

  	spin_lock(&clp->cl_lock);

  	if (list_empty(&cb->cb_per_client)) {
  		/* This is the first call, not a restart */
  		cb->cb_done = false;
  		list_add(&cb->cb_per_client, &clp->cl_callbacks);
  	}

  	spin_unlock(&clp->cl_lock);

  	rpc_call_start(task);
  }

  static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
  {

  	struct nfsd4_callback *cb = calldata;
  	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);

  	struct nfs4_client *clp = dp->dl_client;
  
  	dprintk("%s: minorversion=%d
  ", __func__,

  		clp->cl_minorversion);

  	if (clp->cl_minorversion) {

  		/* No need for lock, access serialized in nfsd4_cb_prepare */

  		++clp->cl_cb_session->se_cb_seq_nr;

  		clear_bit(0, &clp->cl_cb_slot_busy);
  		rpc_wake_up_next(&clp->cl_cb_waitq);
  		dprintk("%s: freed slot, new seqid=%d
  ", __func__,

  			clp->cl_cb_session->se_cb_seq_nr);

  
  		/* We're done looking into the sequence information */
  		task->tk_msg.rpc_resp = NULL;
  	}
  }

  static void nfsd4_cb_recall_done(struct rpc_task *task, void *calldata)
  {

  	struct nfsd4_callback *cb = calldata;
  	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);

  	struct nfs4_client *clp = dp->dl_client;

  	struct rpc_clnt *current_rpc_client = clp->cl_cb_client;

  	nfsd4_cb_done(task, calldata);

  	if (current_rpc_client != task->tk_client) {
  		/* We're shutting down or changing cl_cb_client; leave
  		 * it to nfsd4_process_cb_update to restart the call if
  		 * necessary. */

  		return;
  	}

  	if (cb->cb_done)
  		return;

  	switch (task->tk_status) {

  	case 0:

  		cb->cb_done = true;

  		return;
  	case -EBADHANDLE:
  	case -NFS4ERR_BAD_STATEID:
  		/* Race: client probably got cb_recall
  		 * before open reply granting delegation */
  		break;
  	default:

  		/* Network partition? */

  		nfsd4_mark_cb_down(clp, task->tk_status);

  	}
  	if (dp->dl_retries--) {
  		rpc_delay(task, 2*HZ);
  		task->tk_status = 0;

  		rpc_restart_call_prepare(task);

  		return;

  	}

  	nfsd4_mark_cb_down(clp, task->tk_status);
  	cb->cb_done = true;

  }
  
  static void nfsd4_cb_recall_release(void *calldata)
  {

  	struct nfsd4_callback *cb = calldata;

  	struct nfs4_client *clp = cb->cb_clp;

  	struct nfs4_delegation *dp = container_of(cb, struct nfs4_delegation, dl_recall);

  	if (cb->cb_done) {
  		spin_lock(&clp->cl_lock);
  		list_del(&cb->cb_per_client);
  		spin_unlock(&clp->cl_lock);
  		nfs4_put_delegation(dp);
  	}

  }
  
  static const struct rpc_call_ops nfsd4_cb_recall_ops = {

  	.rpc_call_prepare = nfsd4_cb_prepare,

  	.rpc_call_done = nfsd4_cb_recall_done,
  	.rpc_release = nfsd4_cb_recall_release,
  };

  int nfsd4_create_callback_queue(void)
  {
  	callback_wq = create_singlethread_workqueue("nfsd4_callbacks");
  	if (!callback_wq)
  		return -ENOMEM;
  	return 0;
  }
  
  void nfsd4_destroy_callback_queue(void)
  {
  	destroy_workqueue(callback_wq);
  }

  /* must be called under the state lock */

  void nfsd4_shutdown_callback(struct nfs4_client *clp)

  {

  	set_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags);

  	/*

  	 * Note this won't actually result in a null callback;
  	 * instead, nfsd4_do_callback_rpc() will detect the killed
  	 * client, destroy the rpc client, and stop:

  	 */

  	do_probe_callback(clp);

  	flush_workqueue(callback_wq);

  }

  static void nfsd4_release_cb(struct nfsd4_callback *cb)

  {

  	if (cb->cb_ops->rpc_release)
  		cb->cb_ops->rpc_release(cb);
  }

  /* requires cl_lock: */
  static struct nfsd4_conn * __nfsd4_find_backchannel(struct nfs4_client *clp)
  {
  	struct nfsd4_session *s;
  	struct nfsd4_conn *c;
  
  	list_for_each_entry(s, &clp->cl_sessions, se_perclnt) {
  		list_for_each_entry(c, &s->se_conns, cn_persession) {
  			if (c->cn_flags & NFS4_CDFC4_BACK)
  				return c;
  		}
  	}
  	return NULL;
  }

  static void nfsd4_process_cb_update(struct nfsd4_callback *cb)

  {
  	struct nfs4_cb_conn conn;
  	struct nfs4_client *clp = cb->cb_clp;

  	struct nfsd4_session *ses = NULL;
  	struct nfsd4_conn *c;

  	int err;
  
  	/*
  	 * This is either an update, or the client dying; in either case,
  	 * kill the old client:
  	 */
  	if (clp->cl_cb_client) {
  		rpc_shutdown_client(clp->cl_cb_client);
  		clp->cl_cb_client = NULL;
  	}

  	if (clp->cl_cb_conn.cb_xprt) {
  		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
  		clp->cl_cb_conn.cb_xprt = NULL;
  	}

  	if (test_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags))
  		return;
  	spin_lock(&clp->cl_lock);
  	/*
  	 * Only serialized callback code is allowed to clear these
  	 * flags; main nfsd code can only set them:
  	 */
  	BUG_ON(!clp->cl_cb_flags);
  	clear_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
  	memcpy(&conn, &cb->cb_clp->cl_cb_conn, sizeof(struct nfs4_cb_conn));

  	c = __nfsd4_find_backchannel(clp);
  	if (c) {
  		svc_xprt_get(c->cn_xprt);
  		conn.cb_xprt = c->cn_xprt;
  		ses = c->cn_session;
  	}

  	spin_unlock(&clp->cl_lock);

  	err = setup_callback_client(clp, &conn, ses);

  	if (err) {

  		warn_no_callback_path(clp, err);

  		return;
  	}
  	/* Yay, the callback channel's back! Restart any callbacks: */
  	list_for_each_entry(cb, &clp->cl_callbacks, cb_per_client)
  		run_nfsd4_cb(cb);

  }

  void nfsd4_do_callback_rpc(struct work_struct *w)
  {
  	struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);

  	struct nfs4_client *clp = cb->cb_clp;

  	struct rpc_clnt *clnt;

  	if (clp->cl_cb_flags)
  		nfsd4_process_cb_update(cb);
  
  	clnt = clp->cl_cb_client;
  	if (!clnt) {
  		/* Callback channel broken, or client killed; give up: */

  		nfsd4_release_cb(cb);

  		return;

  	}

  	rpc_call_async(clnt, &cb->cb_msg, RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
  			cb->cb_ops, cb);

  }

  void nfsd4_cb_recall(struct nfs4_delegation *dp)

  {

  	struct nfsd4_callback *cb = &dp->dl_recall;

  	struct nfs4_client *clp = dp->dl_client;

  	dp->dl_retries = 1;

  	cb->cb_op = dp;

  	cb->cb_clp = clp;

  	cb->cb_msg.rpc_proc = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_RECALL];

  	cb->cb_msg.rpc_argp = cb;
  	cb->cb_msg.rpc_resp = cb;

  	cb->cb_msg.rpc_cred = callback_cred;
  
  	cb->cb_ops = &nfsd4_cb_recall_ops;
  	dp->dl_retries = 1;

  	INIT_LIST_HEAD(&cb->cb_per_client);

  	cb->cb_done = true;

  	run_nfsd4_cb(&dp->dl_recall);

  }