nfs4callback.c

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/*
 *  Copyright (c) 2001 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Kendrick Smith <[email protected]>
 *  Andy Adamson <[email protected]>
 *
 *  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

static void nfsd4_mark_cb_fault(struct nfs4_client *, int reason);

#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.\n",
        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\n", 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\n", 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_stid.sc_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\n", __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\n", __func__);
        goto out;
    }

    dummy = be32_to_cpup(p++);
    if (dummy != 0) {
        dprintk("NFS: %s Invalid slotid\n", __func__);
        goto out;
    }

    /*
     * FIXME: process highest slotid and target highest slotid
     */
    status = 0;
out:
    if (status)
        nfsd4_mark_cb_fault(cb->cb_clp, status);
    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 const struct rpc_version *nfs_cb_version[] = {
    &nfs_cb_version4,
};

static const struct rpc_program cb_program;

static struct rpc_stat cb_stats = {
    .program        = &cb_program
};

#define NFS4_CALLBACK 0x40000000
static const 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,
        .flags      = (RPC_CLNT_CREATE_NOPING | RPC_CLNT_CREATE_QUIET),
    };
    struct rpc_clnt *client;

    if (clp->cl_minorversion == 0) {
        if (!clp->cl_cred.cr_principal &&
                (clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
            return -EINVAL;
        args.client_name = clp->cl_cred.cr_principal;
        args.prognumber = conn->cb_prog,
        args.protocol = XPRT_TRANSPORT_TCP;
        args.authflavor = clp->cl_cred.cr_flavor;
        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;
        args.authflavor = RPC_AUTH_UNIX;
    }
    /* Create RPC client */
    client = rpc_create(&args);
    if (IS_ERR(client)) {
        dprintk("NFSD: couldn't create callback client: %ld\n",
            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\n",
        (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_mark_cb_fault(struct nfs4_client *clp, int reason)
{
    clp->cl_cb_state = NFSD4_CB_FAULT;
    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("nfs");
    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)
{
    clp->cl_cb_state = NFSD4_CB_UNKNOWN;
    set_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_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\n", __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_stid.sc_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_stid.sc_client;

    dprintk("%s: minorversion=%d\n", __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\n", __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_stid.sc_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_CB_KILL, &clp->cl_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_CB_KILL, &clp->cl_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_flags & NFSD4_CLIENT_CB_FLAG_MASK));
    clear_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_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) {
        nfsd4_mark_cb_down(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_flags & NFSD4_CLIENT_CB_FLAG_MASK)
        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_stid.sc_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;

    INIT_LIST_HEAD(&cb->cb_per_client);
    cb->cb_done = true;

    run_nfsd4_cb(&dp->dl_recall);
}