drm/i915: use new macros to access the ring start register

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / nfsd / nfs4callback.c

/*
 *  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
#define NFS4_STATEID_SIZE 16

/* Index of predefined Linux callback client operations */

enum {
        NFSPROC4_CLNT_CB_NULL = 0,
        NFSPROC4_CLNT_CB_RECALL,
        NFSPROC4_CLNT_CB_SEQUENCE,
};

enum nfs_cb_opnum4 {
        OP_CB_RECALL            = 4,
        OP_CB_SEQUENCE          = 11,
};

#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)

/*
* Generic encode routines from fs/nfs/nfs4xdr.c
*/
static inline __be32 *
xdr_writemem(__be32 *p, const void *ptr, int nbytes)
{
        int tmp = XDR_QUADLEN(nbytes);
        if (!tmp)
                return p;
        p[tmp-1] = 0;
        memcpy(p, ptr, nbytes);
        return p + tmp;
}

#define WRITE32(n)               *p++ = htonl(n)
#define WRITEMEM(ptr,nbytes)     do {                           \
        p = xdr_writemem(p, ptr, nbytes);                       \
} while (0)
#define RESERVE_SPACE(nbytes)   do {                            \
        p = xdr_reserve_space(xdr, nbytes);                     \
        if (!p) dprintk("NFSD: RESERVE_SPACE(%d) failed in function %s\n", (int) (nbytes), __func__); \
        BUG_ON(!p);                                             \
} while (0)

/*
 * Generic decode routines from fs/nfs/nfs4xdr.c
 */
#define DECODE_TAIL                             \
        status = 0;                             \
out:                                            \
        return status;                          \
xdr_error:                                      \
        dprintk("NFSD: xdr error! (%s:%d)\n", __FILE__, __LINE__); \
        status = -EIO;                          \
        goto out

#define READ32(x)         (x) = ntohl(*p++)
#define READ64(x)         do {                  \
        (x) = (u64)ntohl(*p++) << 32;           \
        (x) |= ntohl(*p++);                     \
} while (0)
#define READTIME(x)       do {                  \
        p++;                                    \
        (x.tv_sec) = ntohl(*p++);               \
        (x.tv_nsec) = ntohl(*p++);              \
} while (0)
#define READ_BUF(nbytes)  do { \
        p = xdr_inline_decode(xdr, nbytes); \
        if (!p) { \
                dprintk("NFSD: %s: reply buffer overflowed in line %d.\n", \
                        __func__, __LINE__); \
                return -EIO; \
        } \
} while (0)

struct nfs4_cb_compound_hdr {
        /* args */
        u32             ident;  /* minorversion 0 only */
        u32             nops;
        __be32          *nops_p;
        u32             minorversion;
        /* res */
        int             status;
};

static 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             }
};

static int
nfs_cb_stat_to_errno(int stat)
{
        int i;
        for (i = 0; nfs_cb_errtbl[i].stat != -1; i++) {
                if (nfs_cb_errtbl[i].stat == stat)
                        return nfs_cb_errtbl[i].errno;
        }
        /* 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.
        */
        return stat;
}

/*
 * XDR encode
 */

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

        RESERVE_SPACE(sizeof(stateid_t));
        WRITE32(sid->si_generation);
        WRITEMEM(&sid->si_opaque, sizeof(stateid_opaque_t));
}

static void
encode_cb_compound_hdr(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr)
{
        __be32 * p;

        RESERVE_SPACE(16);
        WRITE32(0);            /* tag length is always 0 */
        WRITE32(hdr->minorversion);
        WRITE32(hdr->ident);
        hdr->nops_p = p;
        WRITE32(hdr->nops);
}

static void encode_cb_nops(struct nfs4_cb_compound_hdr *hdr)
{
        *hdr->nops_p = htonl(hdr->nops);
}

static void
encode_cb_recall(struct xdr_stream *xdr, struct nfs4_delegation *dp,
                struct nfs4_cb_compound_hdr *hdr)
{
        __be32 *p;
        int len = dp->dl_fh.fh_size;

        RESERVE_SPACE(4);
        WRITE32(OP_CB_RECALL);
        encode_stateid(xdr, &dp->dl_stateid);
        RESERVE_SPACE(8 + (XDR_QUADLEN(len) << 2));
        WRITE32(0); /* truncate optimization not implemented */
        WRITE32(len);
        WRITEMEM(&dp->dl_fh.fh_base, len);
        hdr->nops++;
}

static void
encode_cb_sequence(struct xdr_stream *xdr, struct nfsd4_cb_sequence *args,
                   struct nfs4_cb_compound_hdr *hdr)
{
        __be32 *p;

        if (hdr->minorversion == 0)
                return;

        RESERVE_SPACE(1 + NFS4_MAX_SESSIONID_LEN + 20);

        WRITE32(OP_CB_SEQUENCE);
        WRITEMEM(args->cbs_clp->cl_sessionid.data, NFS4_MAX_SESSIONID_LEN);
        WRITE32(args->cbs_clp->cl_cb_seq_nr);
        WRITE32(0);             /* slotid, always 0 */
        WRITE32(0);             /* highest slotid always 0 */
        WRITE32(0);             /* cachethis always 0 */
        WRITE32(0); /* FIXME: support referring_call_lists */
        hdr->nops++;
}

static int
nfs4_xdr_enc_cb_null(struct rpc_rqst *req, __be32 *p)
{
        struct xdr_stream xdrs, *xdr = &xdrs;

        xdr_init_encode(&xdrs, &req->rq_snd_buf, p);
        RESERVE_SPACE(0);
        return 0;
}

static int
nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, __be32 *p,
                struct nfs4_rpc_args *rpc_args)
{
        struct xdr_stream xdr;
        struct nfs4_delegation *args = rpc_args->args_op;
        struct nfs4_cb_compound_hdr hdr = {
                .ident = args->dl_ident,
                .minorversion = rpc_args->args_seq.cbs_minorversion,
        };

        xdr_init_encode(&xdr, &req->rq_snd_buf, p);
        encode_cb_compound_hdr(&xdr, &hdr);
        encode_cb_sequence(&xdr, &rpc_args->args_seq, &hdr);
        encode_cb_recall(&xdr, args, &hdr);
        encode_cb_nops(&hdr);
        return 0;
}


static int
decode_cb_compound_hdr(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr){
        __be32 *p;
        u32 taglen;

        READ_BUF(8);
        READ32(hdr->status);
        /* We've got no use for the tag; ignore it: */
        READ32(taglen);
        READ_BUF(taglen + 4);
        p += XDR_QUADLEN(taglen);
        READ32(hdr->nops);
        return 0;
}

static int
decode_cb_op_hdr(struct xdr_stream *xdr, enum nfs_opnum4 expected)
{
        __be32 *p;
        u32 op;
        int32_t nfserr;

        READ_BUF(8);
        READ32(op);
        if (op != expected) {
                dprintk("NFSD: decode_cb_op_hdr: Callback server returned "
                         " operation %d but we issued a request for %d\n",
                         op, expected);
                return -EIO;
        }
        READ32(nfserr);
        if (nfserr != NFS_OK)
                return -nfs_cb_stat_to_errno(nfserr);
        return 0;
}

/*
 * Our current back channel implmentation supports a single backchannel
 * with a single slot.
 */
static int
decode_cb_sequence(struct xdr_stream *xdr, struct nfsd4_cb_sequence *res,
                   struct rpc_rqst *rqstp)
{
        struct nfs4_sessionid id;
        int status;
        u32 dummy;
        __be32 *p;

        if (res->cbs_minorversion == 0)
                return 0;

        status = decode_cb_op_hdr(xdr, OP_CB_SEQUENCE);
        if (status)
                return status;

        /*
         * If the server returns different values for sessionID, slotID or
         * sequence number, the server is looney tunes.
         */
        status = -ESERVERFAULT;

        READ_BUF(NFS4_MAX_SESSIONID_LEN + 16);
        memcpy(id.data, p, NFS4_MAX_SESSIONID_LEN);
        p += XDR_QUADLEN(NFS4_MAX_SESSIONID_LEN);
        if (memcmp(id.data, res->cbs_clp->cl_sessionid.data,
                   NFS4_MAX_SESSIONID_LEN)) {
                dprintk("%s Invalid session id\n", __func__);
                goto out;
        }
        READ32(dummy);
        if (dummy != res->cbs_clp->cl_cb_seq_nr) {
                dprintk("%s Invalid sequence number\n", __func__);
                goto out;
        }
        READ32(dummy);  /* slotid must be 0 */
        if (dummy != 0) {
                dprintk("%s Invalid slotid\n", __func__);
                goto out;
        }
        /* FIXME: process highest slotid and target highest slotid */
        status = 0;
out:
        return status;
}


static int
nfs4_xdr_dec_cb_null(struct rpc_rqst *req, __be32 *p)
{
        return 0;
}

static int
nfs4_xdr_dec_cb_recall(struct rpc_rqst *rqstp, __be32 *p,
                struct nfsd4_cb_sequence *seq)
{
        struct xdr_stream xdr;
        struct nfs4_cb_compound_hdr hdr;
        int status;

        xdr_init_decode(&xdr, &rqstp->rq_rcv_buf, p);
        status = decode_cb_compound_hdr(&xdr, &hdr);
        if (status)
                goto out;
        if (seq) {
                status = decode_cb_sequence(&xdr, seq, rqstp);
                if (status)
                        goto out;
        }
        status = decode_cb_op_hdr(&xdr, OP_CB_RECALL);
out:
        return status;
}

/*
 * RPC procedure tables
 */
#define PROC(proc, call, argtype, restype)                              \
[NFSPROC4_CLNT_##proc] = {                                              \
        .p_proc   = NFSPROC4_CB_##call,                                 \
        .p_encode = (kxdrproc_t) nfs4_xdr_##argtype,                    \
        .p_decode = (kxdrproc_t) nfs4_xdr_##restype,                    \
        .p_arglen = NFS4_##argtype##_sz,                                \
        .p_replen = NFS4_##restype##_sz,                                \
        .p_statidx = NFSPROC4_CB_##call,                                \
        .p_name   = #proc,                                              \
}

static struct rpc_procinfo     nfs4_cb_procedures[] = {
    PROC(CB_NULL,      NULL,     enc_cb_null,     dec_cb_null),
    PROC(CB_RECALL,    COMPOUND,   enc_cb_recall,      dec_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;
}

/* Reference counting, callback cleanup, etc., all look racy as heck.
 * And why is cl_cb_set an atomic? */

int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *cb)
{
        struct rpc_timeout      timeparms = {
                .to_initval     = max_cb_time(),
                .to_retries     = 0,
        };
        struct rpc_create_args args = {
                .protocol       = XPRT_TRANSPORT_TCP,
                .address        = (struct sockaddr *) &cb->cb_addr,
                .addrsize       = cb->cb_addrlen,
                .timeout        = &timeparms,
                .program        = &cb_program,
                .prognumber     = cb->cb_prog,
                .version        = 0,
                .authflavor     = clp->cl_flavor,
                .flags          = (RPC_CLNT_CREATE_NOPING | RPC_CLNT_CREATE_QUIET),
                .client_name    = clp->cl_principal,
        };
        struct rpc_clnt *client;

        if (!clp->cl_principal && (clp->cl_flavor >= RPC_AUTH_GSS_KRB5))
                return -EINVAL;
        if (cb->cb_minorversion) {
                args.bc_xprt = cb->cb_xprt;
                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\n",
                        PTR_ERR(client));
                return PTR_ERR(client);
        }
        nfsd4_set_callback_client(clp, 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_cb_probe_done(struct rpc_task *task, void *calldata)
{
        struct nfs4_client *clp = calldata;

        if (task->tk_status)
                warn_no_callback_path(clp, task->tk_status);
        else
                atomic_set(&clp->cl_cb_set, 1);
}

static const struct rpc_call_ops nfsd4_cb_probe_ops = {
        .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;
}


void do_probe_callback(struct nfs4_client *clp)
{
        struct rpc_message msg = {
                .rpc_proc       = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_NULL],
                .rpc_argp       = clp,
                .rpc_cred       = callback_cred
        };
        int status;

        status = rpc_call_async(clp->cl_cb_client, &msg,
                                RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
                                &nfsd4_cb_probe_ops, (void *)clp);
        if (status)
                warn_no_callback_path(clp, status);
}

/*
 * Set up the callback client and put a NFSPROC4_CB_NULL on the wire...
 */
void nfsd4_probe_callback(struct nfs4_client *clp, struct nfs4_cb_conn *cb)
{
        int status;

        BUG_ON(atomic_read(&clp->cl_cb_set));

        status = setup_callback_client(clp, cb);
        if (status) {
                warn_no_callback_path(clp, status);
                return;
        }
        do_probe_callback(clp);
}

/*
 * 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 int nfsd41_cb_setup_sequence(struct nfs4_client *clp,
                struct rpc_task *task)
{
        struct nfs4_rpc_args *args = task->tk_msg.rpc_argp;
        u32 *ptr = (u32 *)clp->cl_sessionid.data;
        int status = 0;

        dprintk("%s: %u:%u:%u:%u\n", __func__,
                ptr[0], ptr[1], ptr[2], ptr[3]);

        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__);
                status = -EAGAIN;
                goto out;
        }

        /*
         * We'll need the clp during XDR encoding and decoding,
         * and the sequence during decoding to verify the reply
         */
        args->args_seq.cbs_clp = clp;
        task->tk_msg.rpc_resp = &args->args_seq;

out:
        dprintk("%s status=%d\n", __func__, status);
        return status;
}

/*
 * 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 nfs4_delegation *dp = calldata;
        struct nfs4_client *clp = dp->dl_client;
        struct nfs4_rpc_args *args = task->tk_msg.rpc_argp;
        u32 minorversion = clp->cl_cb_conn.cb_minorversion;
        int status = 0;

        args->args_seq.cbs_minorversion = minorversion;
        if (minorversion) {
                status = nfsd41_cb_setup_sequence(clp, task);
                if (status) {
                        if (status != -EAGAIN) {
                                /* terminate rpc task */
                                task->tk_status = status;
                                task->tk_action = NULL;
                        }
                        return;
                }
        }
        rpc_call_start(task);
}

static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
{
        struct nfs4_delegation *dp = calldata;
        struct nfs4_client *clp = dp->dl_client;

        dprintk("%s: minorversion=%d\n", __func__,
                clp->cl_cb_conn.cb_minorversion);

        if (clp->cl_cb_conn.cb_minorversion) {
                /* No need for lock, access serialized in nfsd4_cb_prepare */
                ++clp->cl_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_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 nfs4_delegation *dp = calldata;
        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 == NULL) {
                /* We're shutting down; give up. */
                /* XXX: err, or is it ok just to fall through
                 * and rpc_restart_call? */
                return;
        }

        switch (task->tk_status) {
        case 0:
                return;
        case -EBADHANDLE:
        case -NFS4ERR_BAD_STATEID:
                /* Race: client probably got cb_recall
                 * before open reply granting delegation */
                break;
        default:
                /* Network partition? */
                atomic_set(&clp->cl_cb_set, 0);
                warn_no_callback_path(clp, task->tk_status);
                if (current_rpc_client != task->tk_client) {
                        /* queue a callback on the new connection: */
                        atomic_inc(&dp->dl_count);
                        nfsd4_cb_recall(dp);
                        return;
                }
        }
        if (dp->dl_retries--) {
                rpc_delay(task, 2*HZ);
                task->tk_status = 0;
                rpc_restart_call_prepare(task);
                return;
        } else {
                atomic_set(&clp->cl_cb_set, 0);
                warn_no_callback_path(clp, task->tk_status);
        }
}

static void nfsd4_cb_recall_release(void *calldata)
{
        struct nfs4_delegation *dp = calldata;

        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,
};

static struct workqueue_struct *callback_wq;

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_set_callback_client(struct nfs4_client *clp, struct rpc_clnt *new)
{
        struct rpc_clnt *old = clp->cl_cb_client;

        clp->cl_cb_client = new;
        /*
         * After this, any work that saw the old value of cl_cb_client will
         * be gone:
         */
        flush_workqueue(callback_wq);
        /* So we can safely shut it down: */
        if (old)
                rpc_shutdown_client(old);
}

/*
 * called with dp->dl_count inc'ed.
 */
static void _nfsd4_cb_recall(struct nfs4_delegation *dp)
{
        struct nfs4_client *clp = dp->dl_client;
        struct rpc_clnt *clnt = clp->cl_cb_client;
        struct nfs4_rpc_args *args = &dp->dl_recall.cb_args;
        struct rpc_message msg = {
                .rpc_proc = &nfs4_cb_procedures[NFSPROC4_CLNT_CB_RECALL],
                .rpc_cred = callback_cred
        };

        if (clnt == NULL) {
                nfs4_put_delegation(dp);
                return; /* Client is shutting down; give up. */
        }

        args->args_op = dp;
        msg.rpc_argp = args;
        dp->dl_retries = 1;
        rpc_call_async(clnt, &msg, RPC_TASK_SOFT, &nfsd4_cb_recall_ops, dp);
}

void nfsd4_do_callback_rpc(struct work_struct *w)
{
        /* XXX: for now, just send off delegation recall. */
        /* In future, generalize to handle any sort of callback. */
        struct nfsd4_callback *c = container_of(w, struct nfsd4_callback, cb_work);
        struct nfs4_delegation *dp = container_of(c, struct nfs4_delegation, dl_recall);

        _nfsd4_cb_recall(dp);
}


void nfsd4_cb_recall(struct nfs4_delegation *dp)
{
        queue_work(callback_wq, &dp->dl_recall.cb_work);
}