/*
 * fs/nfs/nfs4session.c
 *
 * Copyright (c) 2012 Trond Myklebust <Trond.Myklebust@netapp.com>
 *
 */
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/sunrpc/sched.h>
#include <linux/sunrpc/bc_xprt.h>
#include <linux/nfs.h>
#include <linux/nfs4.h>
#include <linux/nfs_fs.h>
#include <linux/module.h>

#include "nfs4_fs.h"
#include "internal.h"
#include "nfs4session.h"
#include "callback.h"

#define NFSDBG_FACILITY         NFSDBG_STATE

/*
 * nfs4_shrink_slot_table - free retired slots from the slot table
 */
static void nfs4_shrink_slot_table(struct nfs4_slot_table  *tbl, u32 newsize)
{
        struct nfs4_slot **p;
        if (newsize >= tbl->max_slots)
                return;

        p = &tbl->slots;
        while (newsize--)
                p = &(*p)->next;
        while (*p) {
                struct nfs4_slot *slot = *p;

                *p = slot->next;
                kfree(slot);
                tbl->max_slots--;
        }
}

/*
 * nfs4_free_slot - free a slot and efficiently update slot table.
 *
 * freeing a slot is trivially done by clearing its respective bit
 * in the bitmap.
 * If the freed slotid equals highest_used_slotid we want to update it
 * so that the server would be able to size down the slot table if needed,
 * otherwise we know that the highest_used_slotid is still in use.
 * When updating highest_used_slotid there may be "holes" in the bitmap
 * so we need to scan down from highest_used_slotid to 0 looking for the now
 * highest slotid in use.
 * If none found, highest_used_slotid is set to NFS4_NO_SLOT.
 *
 * Must be called while holding tbl->slot_tbl_lock
 */
void nfs4_free_slot(struct nfs4_slot_table *tbl, struct nfs4_slot *slot)
{
        u32 slotid = slot->slot_nr;

        /* clear used bit in bitmap */
        __clear_bit(slotid, tbl->used_slots);

        /* update highest_used_slotid when it is freed */
        if (slotid == tbl->highest_used_slotid) {
                u32 new_max = find_last_bit(tbl->used_slots, slotid);
                if (new_max < slotid)
                        tbl->highest_used_slotid = new_max;
                else {
                        tbl->highest_used_slotid = NFS4_NO_SLOT;
                        nfs4_slot_tbl_drain_complete(tbl);
                }
        }
        dprintk("%s: slotid %u highest_used_slotid %d\n", __func__,
                slotid, tbl->highest_used_slotid);
}

static struct nfs4_slot *nfs4_new_slot(struct nfs4_slot_table  *tbl,
                u32 slotid, u32 seq_init, gfp_t gfp_mask)
{
        struct nfs4_slot *slot;

        slot = kzalloc(sizeof(*slot), gfp_mask);
        if (slot) {
                slot->table = tbl;
                slot->slot_nr = slotid;
                slot->seq_nr = seq_init;
        }
        return slot;
}

static struct nfs4_slot *nfs4_find_or_create_slot(struct nfs4_slot_table  *tbl,
                u32 slotid, u32 seq_init, gfp_t gfp_mask)
{
        struct nfs4_slot **p, *slot;

        p = &tbl->slots;
        for (;;) {
                if (*p == NULL) {
                        *p = nfs4_new_slot(tbl, tbl->max_slots,
                                        seq_init, gfp_mask);
                        if (*p == NULL)
                                break;
                        tbl->max_slots++;
                }
                slot = *p;
                if (slot->slot_nr == slotid)
                        return slot;
                p = &slot->next;
        }
        return ERR_PTR(-ENOMEM);
}

/*
 * nfs4_alloc_slot - efficiently look for a free slot
 *
 * nfs4_alloc_slot looks for an unset bit in the used_slots bitmap.
 * If found, we mark the slot as used, update the highest_used_slotid,
 * and respectively set up the sequence operation args.
 *
 * Note: must be called with under the slot_tbl_lock.
 */
struct nfs4_slot *nfs4_alloc_slot(struct nfs4_slot_table *tbl)
{
        struct nfs4_slot *ret = ERR_PTR(-EBUSY);
        u32 slotid;

        dprintk("--> %s used_slots=%04lx highest_used=%u max_slots=%u\n",
                __func__, tbl->used_slots[0], tbl->highest_used_slotid,
                tbl->max_slotid + 1);
        slotid = find_first_zero_bit(tbl->used_slots, tbl->max_slotid + 1);
        if (slotid > tbl->max_slotid)
                goto out;
        ret = nfs4_find_or_create_slot(tbl, slotid, 1, GFP_NOWAIT);
        if (IS_ERR(ret))
                goto out;
        __set_bit(slotid, tbl->used_slots);
        if (slotid > tbl->highest_used_slotid ||
                        tbl->highest_used_slotid == NFS4_NO_SLOT)
                tbl->highest_used_slotid = slotid;
        ret->generation = tbl->generation;

out:
        dprintk("<-- %s used_slots=%04lx highest_used=%d slotid=%d \n",
                __func__, tbl->used_slots[0], tbl->highest_used_slotid,
                !IS_ERR(ret) ? ret->slot_nr : -1);
        return ret;
}

static int nfs4_grow_slot_table(struct nfs4_slot_table *tbl,
                 u32 max_reqs, u32 ivalue)
{
        if (max_reqs <= tbl->max_slots)
                return 0;
        if (!IS_ERR(nfs4_find_or_create_slot(tbl, max_reqs - 1, ivalue, GFP_NOFS)))
                return 0;
        return -ENOMEM;
}

static void nfs4_reset_slot_table(struct nfs4_slot_table *tbl,
                u32 server_highest_slotid,
                u32 ivalue)
{
        struct nfs4_slot **p;

        nfs4_shrink_slot_table(tbl, server_highest_slotid + 1);
        p = &tbl->slots;
        while (*p) {
                (*p)->seq_nr = ivalue;
                (*p)->interrupted = 0;
                p = &(*p)->next;
        }
        tbl->highest_used_slotid = NFS4_NO_SLOT;
        tbl->target_highest_slotid = server_highest_slotid;
        tbl->server_highest_slotid = server_highest_slotid;
        tbl->d_target_highest_slotid = 0;
        tbl->d2_target_highest_slotid = 0;
        tbl->max_slotid = server_highest_slotid;
}

/*
 * (re)Initialise a slot table
 */
static int nfs4_realloc_slot_table(struct nfs4_slot_table *tbl,
                u32 max_reqs, u32 ivalue)
{
        int ret;

        dprintk("--> %s: max_reqs=%u, tbl->max_slots %d\n", __func__,
                max_reqs, tbl->max_slots);

        if (max_reqs > NFS4_MAX_SLOT_TABLE)
                max_reqs = NFS4_MAX_SLOT_TABLE;

        ret = nfs4_grow_slot_table(tbl, max_reqs, ivalue);
        if (ret)
                goto out;

        spin_lock(&tbl->slot_tbl_lock);
        nfs4_reset_slot_table(tbl, max_reqs - 1, ivalue);
        spin_unlock(&tbl->slot_tbl_lock);

        dprintk("%s: tbl=%p slots=%p max_slots=%d\n", __func__,
                tbl, tbl->slots, tbl->max_slots);
out:
        dprintk("<-- %s: return %d\n", __func__, ret);
        return ret;
}

/* Destroy the slot table */
static void nfs4_destroy_slot_tables(struct nfs4_session *session)
{
        nfs4_shrink_slot_table(&session->fc_slot_table, 0);
        nfs4_shrink_slot_table(&session->bc_slot_table, 0);
}

static bool nfs41_assign_slot(struct rpc_task *task, void *pslot)
{
        struct nfs4_sequence_args *args = task->tk_msg.rpc_argp;
        struct nfs4_sequence_res *res = task->tk_msg.rpc_resp;
        struct nfs4_slot *slot = pslot;
        struct nfs4_slot_table *tbl = slot->table;

        if (nfs4_slot_tbl_draining(tbl) && !args->sa_privileged)
                return false;
        slot->generation = tbl->generation;
        args->sa_slot = slot;
        res->sr_timestamp = jiffies;
        res->sr_slot = slot;
        res->sr_status_flags = 0;
        res->sr_status = 1;
        return true;
}

static bool __nfs41_wake_and_assign_slot(struct nfs4_slot_table *tbl,
                struct nfs4_slot *slot)
{
        if (rpc_wake_up_first(&tbl->slot_tbl_waitq, nfs41_assign_slot, slot))
                return true;
        return false;
}

bool nfs41_wake_and_assign_slot(struct nfs4_slot_table *tbl,
                struct nfs4_slot *slot)
{
        if (slot->slot_nr > tbl->max_slotid)
                return false;
        return __nfs41_wake_and_assign_slot(tbl, slot);
}

static bool nfs41_try_wake_next_slot_table_entry(struct nfs4_slot_table *tbl)
{
        struct nfs4_slot *slot = nfs4_alloc_slot(tbl);
        if (!IS_ERR(slot)) {
                bool ret = __nfs41_wake_and_assign_slot(tbl, slot);
                if (ret)
                        return ret;
                nfs4_free_slot(tbl, slot);
        }
        return false;
}

void nfs41_wake_slot_table(struct nfs4_slot_table *tbl)
{
        for (;;) {
                if (!nfs41_try_wake_next_slot_table_entry(tbl))
                        break;
        }
}

static void nfs41_set_max_slotid_locked(struct nfs4_slot_table *tbl,
                u32 target_highest_slotid)
{
        u32 max_slotid;

        max_slotid = min(NFS4_MAX_SLOT_TABLE - 1, target_highest_slotid);
        if (max_slotid > tbl->server_highest_slotid)
                max_slotid = tbl->server_highest_slotid;
        if (max_slotid > tbl->target_highest_slotid)
                max_slotid = tbl->target_highest_slotid;
        tbl->max_slotid = max_slotid;
        nfs41_wake_slot_table(tbl);
}

/* Update the client's idea of target_highest_slotid */
static void nfs41_set_target_slotid_locked(struct nfs4_slot_table *tbl,
                u32 target_highest_slotid)
{
        if (tbl->target_highest_slotid == target_highest_slotid)
                return;
        tbl->target_highest_slotid = target_highest_slotid;
        tbl->generation++;
}

void nfs41_set_target_slotid(struct nfs4_slot_table *tbl,
                u32 target_highest_slotid)
{
        spin_lock(&tbl->slot_tbl_lock);
        nfs41_set_target_slotid_locked(tbl, target_highest_slotid);
        tbl->d_target_highest_slotid = 0;
        tbl->d2_target_highest_slotid = 0;
        nfs41_set_max_slotid_locked(tbl, target_highest_slotid);
        spin_unlock(&tbl->slot_tbl_lock);
}

static void nfs41_set_server_slotid_locked(struct nfs4_slot_table *tbl,
                u32 highest_slotid)
{
        if (tbl->server_highest_slotid == highest_slotid)
                return;
        if (tbl->highest_used_slotid > highest_slotid)
                return;
        /* Deallocate slots */
        nfs4_shrink_slot_table(tbl, highest_slotid + 1);
        tbl->server_highest_slotid = highest_slotid;
}

static s32 nfs41_derivative_target_slotid(s32 s1, s32 s2)
{
        s1 -= s2;
        if (s1 == 0)
                return 0;
        if (s1 < 0)
                return (s1 - 1) >> 1;
        return (s1 + 1) >> 1;
}

static int nfs41_sign_s32(s32 s1)
{
        if (s1 > 0)
                return 1;
        if (s1 < 0)
                return -1;
        return 0;
}

static bool nfs41_same_sign_or_zero_s32(s32 s1, s32 s2)
{
        if (!s1 || !s2)
                return true;
        return nfs41_sign_s32(s1) == nfs41_sign_s32(s2);
}

/* Try to eliminate outliers by checking for sharp changes in the
 * derivatives and second derivatives
 */
static bool nfs41_is_outlier_target_slotid(struct nfs4_slot_table *tbl,
                u32 new_target)
{
        s32 d_target, d2_target;
        bool ret = true;

        d_target = nfs41_derivative_target_slotid(new_target,
                        tbl->target_highest_slotid);
        d2_target = nfs41_derivative_target_slotid(d_target,
                        tbl->d_target_highest_slotid);
        /* Is first derivative same sign? */
        if (nfs41_same_sign_or_zero_s32(d_target, tbl->d_target_highest_slotid))
                ret = false;
        /* Is second derivative same sign? */
        if (nfs41_same_sign_or_zero_s32(d2_target, tbl->d2_target_highest_slotid))
                ret = false;
        tbl->d_target_highest_slotid = d_target;
        tbl->d2_target_highest_slotid = d2_target;
        return ret;
}

void nfs41_update_target_slotid(struct nfs4_slot_table *tbl,
                struct nfs4_slot *slot,
                struct nfs4_sequence_res *res)
{
        spin_lock(&tbl->slot_tbl_lock);
        if (!nfs41_is_outlier_target_slotid(tbl, res->sr_target_highest_slotid))
                nfs41_set_target_slotid_locked(tbl, res->sr_target_highest_slotid);
        if (tbl->generation == slot->generation)
                nfs41_set_server_slotid_locked(tbl, res->sr_highest_slotid);
        nfs41_set_max_slotid_locked(tbl, res->sr_target_highest_slotid);
        spin_unlock(&tbl->slot_tbl_lock);
}

/*
 * Initialize or reset the forechannel and backchannel tables
 */
int nfs4_setup_session_slot_tables(struct nfs4_session *ses)
{
        struct nfs4_slot_table *tbl;
        int status;

        dprintk("--> %s\n", __func__);
        /* Fore channel */
        tbl = &ses->fc_slot_table;
        tbl->session = ses;
        status = nfs4_realloc_slot_table(tbl, ses->fc_attrs.max_reqs, 1);
        if (status) /* -ENOMEM */
                return status;
        /* Back channel */
        tbl = &ses->bc_slot_table;
        tbl->session = ses;
        status = nfs4_realloc_slot_table(tbl, ses->bc_attrs.max_reqs, 0);
        if (status && tbl->slots == NULL)
                /* Fore and back channel share a connection so get
                 * both slot tables or neither */
                nfs4_destroy_slot_tables(ses);
        return status;
}

struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp)
{
        struct nfs4_session *session;
        struct nfs4_slot_table *tbl;

        session = kzalloc(sizeof(struct nfs4_session), GFP_NOFS);
        if (!session)
                return NULL;

        tbl = &session->fc_slot_table;
        tbl->highest_used_slotid = NFS4_NO_SLOT;
        spin_lock_init(&tbl->slot_tbl_lock);
        rpc_init_priority_wait_queue(&tbl->slot_tbl_waitq, "ForeChannel Slot table");
        init_completion(&tbl->complete);

        tbl = &session->bc_slot_table;
        tbl->highest_used_slotid = NFS4_NO_SLOT;
        spin_lock_init(&tbl->slot_tbl_lock);
        rpc_init_wait_queue(&tbl->slot_tbl_waitq, "BackChannel Slot table");
        init_completion(&tbl->complete);

        session->session_state = 1<<NFS4_SESSION_INITING;

        session->clp = clp;
        return session;
}

void nfs4_destroy_session(struct nfs4_session *session)
{
        struct rpc_xprt *xprt;
        struct rpc_cred *cred;

        cred = nfs4_get_exchange_id_cred(session->clp);
        nfs4_proc_destroy_session(session, cred);
        if (cred)
                put_rpccred(cred);

        rcu_read_lock();
        xprt = rcu_dereference(session->clp->cl_rpcclient->cl_xprt);
        rcu_read_unlock();
        dprintk("%s Destroy backchannel for xprt %p\n",
                __func__, xprt);
        xprt_destroy_backchannel(xprt, NFS41_BC_MIN_CALLBACKS);
        nfs4_destroy_slot_tables(session);
        kfree(session);
}

/*
 * With sessions, the client is not marked ready until after a
 * successful EXCHANGE_ID and CREATE_SESSION.
 *
 * Map errors cl_cons_state errors to EPROTONOSUPPORT to indicate
 * other versions of NFS can be tried.
 */
static int nfs41_check_session_ready(struct nfs_client *clp)
{
        int ret;
        
        if (clp->cl_cons_state == NFS_CS_SESSION_INITING) {
                ret = nfs4_client_recover_expired_lease(clp);
                if (ret)
                        return ret;
        }
        if (clp->cl_cons_state < NFS_CS_READY)
                return -EPROTONOSUPPORT;
        smp_rmb();
        return 0;
}

int nfs4_init_session(struct nfs_client *clp)
{
        if (!nfs4_has_session(clp))
                return 0;

        clear_bit(NFS4_SESSION_INITING, &clp->cl_session->session_state);
        return nfs41_check_session_ready(clp);
}

int nfs4_init_ds_session(struct nfs_client *clp, unsigned long lease_time)
{
        struct nfs4_session *session = clp->cl_session;
        int ret;

        spin_lock(&clp->cl_lock);
        if (test_and_clear_bit(NFS4_SESSION_INITING, &session->session_state)) {
                /*
                 * Do not set NFS_CS_CHECK_LEASE_TIME instead set the
                 * DS lease to be equal to the MDS lease.
                 */
                clp->cl_lease_time = lease_time;
                clp->cl_last_renewal = jiffies;
        }
        spin_unlock(&clp->cl_lock);

        ret = nfs41_check_session_ready(clp);
        if (ret)
                return ret;
        /* Test for the DS role */
        if (!is_ds_client(clp))
                return -ENODEV;
        return 0;
}
EXPORT_SYMBOL_GPL(nfs4_init_ds_session);