knfsd: fix cache.c comment

[linux-2.6/kmemtrace.git] / net / sunrpc / cache.c

/*
 * net/sunrpc/cache.c
 *
 * Generic code for various authentication-related caches
 * used by sunrpc clients and servers.
 *
 * Copyright (C) 2002 Neil Brown <neilb@cse.unsw.edu.au>
 *
 * Released under terms in GPL version 2.  See COPYING.
 *
 */

#include <linux/types.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kmod.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/ctype.h>
#include <asm/uaccess.h>
#include <linux/poll.h>
#include <linux/seq_file.h>
#include <linux/proc_fs.h>
#include <linux/net.h>
#include <linux/workqueue.h>
#include <linux/mutex.h>
#include <asm/ioctls.h>
#include <linux/sunrpc/types.h>
#include <linux/sunrpc/cache.h>
#include <linux/sunrpc/stats.h>

#define  RPCDBG_FACILITY RPCDBG_CACHE

static int cache_defer_req(struct cache_req *req, struct cache_head *item);
static void cache_revisit_request(struct cache_head *item);

static void cache_init(struct cache_head *h)
{
        time_t now = get_seconds();
        h->next = NULL;
        h->flags = 0;
        kref_init(&h->ref);
        h->expiry_time = now + CACHE_NEW_EXPIRY;
        h->last_refresh = now;
}

struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
                                       struct cache_head *key, int hash)
{
        struct cache_head **head,  **hp;
        struct cache_head *new = NULL;

        head = &detail->hash_table[hash];

        read_lock(&detail->hash_lock);

        for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
                struct cache_head *tmp = *hp;
                if (detail->match(tmp, key)) {
                        cache_get(tmp);
                        read_unlock(&detail->hash_lock);
                        return tmp;
                }
        }
        read_unlock(&detail->hash_lock);
        /* Didn't find anything, insert an empty entry */

        new = detail->alloc();
        if (!new)
                return NULL;
        /* must fully initialise 'new', else
         * we might get lose if we need to
         * cache_put it soon.
         */
        cache_init(new);
        detail->init(new, key);

        write_lock(&detail->hash_lock);

        /* check if entry appeared while we slept */
        for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
                struct cache_head *tmp = *hp;
                if (detail->match(tmp, key)) {
                        cache_get(tmp);
                        write_unlock(&detail->hash_lock);
                        cache_put(new, detail);
                        return tmp;
                }
        }
        new->next = *head;
        *head = new;
        detail->entries++;
        cache_get(new);
        write_unlock(&detail->hash_lock);

        return new;
}
EXPORT_SYMBOL(sunrpc_cache_lookup);


static void queue_loose(struct cache_detail *detail, struct cache_head *ch);

static int cache_fresh_locked(struct cache_head *head, time_t expiry)
{
        head->expiry_time = expiry;
        head->last_refresh = get_seconds();
        return !test_and_set_bit(CACHE_VALID, &head->flags);
}

static void cache_fresh_unlocked(struct cache_head *head,
                        struct cache_detail *detail, int new)
{
        if (new)
                cache_revisit_request(head);
        if (test_and_clear_bit(CACHE_PENDING, &head->flags)) {
                cache_revisit_request(head);
                queue_loose(detail, head);
        }
}

struct cache_head *sunrpc_cache_update(struct cache_detail *detail,
                                       struct cache_head *new, struct cache_head *old, int hash)
{
        /* The 'old' entry is to be replaced by 'new'.
         * If 'old' is not VALID, we update it directly,
         * otherwise we need to replace it
         */
        struct cache_head **head;
        struct cache_head *tmp;
        int is_new;

        if (!test_bit(CACHE_VALID, &old->flags)) {
                write_lock(&detail->hash_lock);
                if (!test_bit(CACHE_VALID, &old->flags)) {
                        if (test_bit(CACHE_NEGATIVE, &new->flags))
                                set_bit(CACHE_NEGATIVE, &old->flags);
                        else
                                detail->update(old, new);
                        is_new = cache_fresh_locked(old, new->expiry_time);
                        write_unlock(&detail->hash_lock);
                        cache_fresh_unlocked(old, detail, is_new);
                        return old;
                }
                write_unlock(&detail->hash_lock);
        }
        /* We need to insert a new entry */
        tmp = detail->alloc();
        if (!tmp) {
                cache_put(old, detail);
                return NULL;
        }
        cache_init(tmp);
        detail->init(tmp, old);
        head = &detail->hash_table[hash];

        write_lock(&detail->hash_lock);
        if (test_bit(CACHE_NEGATIVE, &new->flags))
                set_bit(CACHE_NEGATIVE, &tmp->flags);
        else
                detail->update(tmp, new);
        tmp->next = *head;
        *head = tmp;
        detail->entries++;
        cache_get(tmp);
        is_new = cache_fresh_locked(tmp, new->expiry_time);
        cache_fresh_locked(old, 0);
        write_unlock(&detail->hash_lock);
        cache_fresh_unlocked(tmp, detail, is_new);
        cache_fresh_unlocked(old, detail, 0);
        cache_put(old, detail);
        return tmp;
}
EXPORT_SYMBOL(sunrpc_cache_update);

static int cache_make_upcall(struct cache_detail *detail, struct cache_head *h);
/*
 * This is the generic cache management routine for all
 * the authentication caches.
 * It checks the currency of a cache item and will (later)
 * initiate an upcall to fill it if needed.
 *
 *
 * Returns 0 if the cache_head can be used, or cache_puts it and returns
 * -EAGAIN if upcall is pending,
 * -ETIMEDOUT if upcall failed and should be retried,
 * -ENOENT if cache entry was negative
 */
int cache_check(struct cache_detail *detail,
                    struct cache_head *h, struct cache_req *rqstp)
{
        int rv;
        long refresh_age, age;

        /* First decide return status as best we can */
        if (!test_bit(CACHE_VALID, &h->flags) ||
            h->expiry_time < get_seconds())
                rv = -EAGAIN;
        else if (detail->flush_time > h->last_refresh)
                rv = -EAGAIN;
        else {
                /* entry is valid */
                if (test_bit(CACHE_NEGATIVE, &h->flags))
                        rv = -ENOENT;
                else rv = 0;
        }

        /* now see if we want to start an upcall */
        refresh_age = (h->expiry_time - h->last_refresh);
        age = get_seconds() - h->last_refresh;

        if (rqstp == NULL) {
                if (rv == -EAGAIN)
                        rv = -ENOENT;
        } else if (rv == -EAGAIN || age > refresh_age/2) {
                dprintk("RPC:       Want update, refage=%ld, age=%ld\n",
                                refresh_age, age);
                if (!test_and_set_bit(CACHE_PENDING, &h->flags)) {
                        switch (cache_make_upcall(detail, h)) {
                        case -EINVAL:
                                clear_bit(CACHE_PENDING, &h->flags);
                                if (rv == -EAGAIN) {
                                        set_bit(CACHE_NEGATIVE, &h->flags);
                                        cache_fresh_unlocked(h, detail,
                                             cache_fresh_locked(h, get_seconds()+CACHE_NEW_EXPIRY));
                                        rv = -ENOENT;
                                }
                                break;

                        case -EAGAIN:
                                clear_bit(CACHE_PENDING, &h->flags);
                                cache_revisit_request(h);
                                break;
                        }
                }
        }

        if (rv == -EAGAIN)
                if (cache_defer_req(rqstp, h) != 0)
                        rv = -ETIMEDOUT;

        if (rv)
                cache_put(h, detail);
        return rv;
}

/*
 * caches need to be periodically cleaned.
 * For this we maintain a list of cache_detail and
 * a current pointer into that list and into the table
 * for that entry.
 *
 * Each time clean_cache is called it finds the next non-empty entry
 * in the current table and walks the list in that entry
 * looking for entries that can be removed.
 *
 * An entry gets removed if:
 * - The expiry is before current time
 * - The last_refresh time is before the flush_time for that cache
 *
 * later we might drop old entries with non-NEVER expiry if that table
 * is getting 'full' for some definition of 'full'
 *
 * The question of "how often to scan a table" is an interesting one
 * and is answered in part by the use of the "nextcheck" field in the
 * cache_detail.
 * When a scan of a table begins, the nextcheck field is set to a time
 * that is well into the future.
 * While scanning, if an expiry time is found that is earlier than the
 * current nextcheck time, nextcheck is set to that expiry time.
 * If the flush_time is ever set to a time earlier than the nextcheck
 * time, the nextcheck time is then set to that flush_time.
 *
 * A table is then only scanned if the current time is at least
 * the nextcheck time.
 *
 */

static LIST_HEAD(cache_list);
static DEFINE_SPINLOCK(cache_list_lock);
static struct cache_detail *current_detail;
static int current_index;

static const struct file_operations cache_file_operations;
static const struct file_operations content_file_operations;
static const struct file_operations cache_flush_operations;

static void do_cache_clean(struct work_struct *work);
static DECLARE_DELAYED_WORK(cache_cleaner, do_cache_clean);

void cache_register(struct cache_detail *cd)
{
        cd->proc_ent = proc_mkdir(cd->name, proc_net_rpc);
        if (cd->proc_ent) {
                struct proc_dir_entry *p;
                cd->proc_ent->owner = cd->owner;
                cd->channel_ent = cd->content_ent = NULL;

                p = create_proc_entry("flush", S_IFREG|S_IRUSR|S_IWUSR,
                                      cd->proc_ent);
                cd->flush_ent =  p;
                if (p) {
                        p->proc_fops = &cache_flush_operations;
                        p->owner = cd->owner;
                        p->data = cd;
                }

                if (cd->cache_request || cd->cache_parse) {
                        p = create_proc_entry("channel", S_IFREG|S_IRUSR|S_IWUSR,
                                              cd->proc_ent);
                        cd->channel_ent = p;
                        if (p) {
                                p->proc_fops = &cache_file_operations;
                                p->owner = cd->owner;
                                p->data = cd;
                        }
                }
                if (cd->cache_show) {
                        p = create_proc_entry("content", S_IFREG|S_IRUSR|S_IWUSR,
                                              cd->proc_ent);
                        cd->content_ent = p;
                        if (p) {
                                p->proc_fops = &content_file_operations;
                                p->owner = cd->owner;
                                p->data = cd;
                        }
                }
        }
        rwlock_init(&cd->hash_lock);
        INIT_LIST_HEAD(&cd->queue);
        spin_lock(&cache_list_lock);
        cd->nextcheck = 0;
        cd->entries = 0;
        atomic_set(&cd->readers, 0);
        cd->last_close = 0;
        cd->last_warn = -1;
        list_add(&cd->others, &cache_list);
        spin_unlock(&cache_list_lock);

        /* start the cleaning process */
        schedule_delayed_work(&cache_cleaner, 0);
}

int cache_unregister(struct cache_detail *cd)
{
        cache_purge(cd);
        spin_lock(&cache_list_lock);
        write_lock(&cd->hash_lock);
        if (cd->entries || atomic_read(&cd->inuse)) {
                write_unlock(&cd->hash_lock);
                spin_unlock(&cache_list_lock);
                return -EBUSY;
        }
        if (current_detail == cd)
                current_detail = NULL;
        list_del_init(&cd->others);
        write_unlock(&cd->hash_lock);
        spin_unlock(&cache_list_lock);
        if (cd->proc_ent) {
                if (cd->flush_ent)
                        remove_proc_entry("flush", cd->proc_ent);
                if (cd->channel_ent)
                        remove_proc_entry("channel", cd->proc_ent);
                if (cd->content_ent)
                        remove_proc_entry("content", cd->proc_ent);

                cd->proc_ent = NULL;
                remove_proc_entry(cd->name, proc_net_rpc);
        }
        if (list_empty(&cache_list)) {
                /* module must be being unloaded so its safe to kill the worker */
                cancel_delayed_work_sync(&cache_cleaner);
        }
        return 0;
}

/* clean cache tries to find something to clean
 * and cleans it.
 * It returns 1 if it cleaned something,
 *            0 if it didn't find anything this time
 *           -1 if it fell off the end of the list.
 */
static int cache_clean(void)
{
        int rv = 0;
        struct list_head *next;

        spin_lock(&cache_list_lock);

        /* find a suitable table if we don't already have one */
        while (current_detail == NULL ||
            current_index >= current_detail->hash_size) {
                if (current_detail)
                        next = current_detail->others.next;
                else
                        next = cache_list.next;
                if (next == &cache_list) {
                        current_detail = NULL;
                        spin_unlock(&cache_list_lock);
                        return -1;
                }
                current_detail = list_entry(next, struct cache_detail, others);
                if (current_detail->nextcheck > get_seconds())
                        current_index = current_detail->hash_size;
                else {
                        current_index = 0;
                        current_detail->nextcheck = get_seconds()+30*60;
                }
        }

        /* find a non-empty bucket in the table */
        while (current_detail &&
               current_index < current_detail->hash_size &&
               current_detail->hash_table[current_index] == NULL)
                current_index++;

        /* find a cleanable entry in the bucket and clean it, or set to next bucket */

        if (current_detail && current_index < current_detail->hash_size) {
                struct cache_head *ch, **cp;
                struct cache_detail *d;

                write_lock(&current_detail->hash_lock);

                /* Ok, now to clean this strand */

                cp = & current_detail->hash_table[current_index];
                ch = *cp;
                for (; ch; cp= & ch->next, ch= *cp) {
                        if (current_detail->nextcheck > ch->expiry_time)
                                current_detail->nextcheck = ch->expiry_time+1;
                        if (ch->expiry_time >= get_seconds()
                            && ch->last_refresh >= current_detail->flush_time
                                )
                                continue;
                        if (test_and_clear_bit(CACHE_PENDING, &ch->flags))
                                queue_loose(current_detail, ch);

                        if (atomic_read(&ch->ref.refcount) == 1)
                                break;
                }
                if (ch) {
                        *cp = ch->next;
                        ch->next = NULL;
                        current_detail->entries--;
                        rv = 1;
                }
                write_unlock(&current_detail->hash_lock);
                d = current_detail;
                if (!ch)
                        current_index ++;
                spin_unlock(&cache_list_lock);
                if (ch)
                        cache_put(ch, d);
        } else
                spin_unlock(&cache_list_lock);

        return rv;
}

/*
 * We want to regularly clean the cache, so we need to schedule some work ...
 */
static void do_cache_clean(struct work_struct *work)
{
        int delay = 5;
        if (cache_clean() == -1)
                delay = 30*HZ;

        if (list_empty(&cache_list))
                delay = 0;

        if (delay)
                schedule_delayed_work(&cache_cleaner, delay);
}


/*
 * Clean all caches promptly.  This just calls cache_clean
 * repeatedly until we are sure that every cache has had a chance to
 * be fully cleaned
 */
void cache_flush(void)
{
        while (cache_clean() != -1)
                cond_resched();
        while (cache_clean() != -1)
                cond_resched();
}

void cache_purge(struct cache_detail *detail)
{
        detail->flush_time = LONG_MAX;
        detail->nextcheck = get_seconds();
        cache_flush();
        detail->flush_time = 1;
}



/*
 * Deferral and Revisiting of Requests.
 *
 * If a cache lookup finds a pending entry, we
 * need to defer the request and revisit it later.
 * All deferred requests are stored in a hash table,
 * indexed by "struct cache_head *".
 * As it may be wasteful to store a whole request
 * structure, we allow the request to provide a
 * deferred form, which must contain a
 * 'struct cache_deferred_req'
 * This cache_deferred_req contains a method to allow
 * it to be revisited when cache info is available
 */

#define DFR_HASHSIZE    (PAGE_SIZE/sizeof(struct list_head))
#define DFR_HASH(item)  ((((long)item)>>4 ^ (((long)item)>>13)) % DFR_HASHSIZE)

#define DFR_MAX 300     /* ??? */

static DEFINE_SPINLOCK(cache_defer_lock);
static LIST_HEAD(cache_defer_list);
static struct list_head cache_defer_hash[DFR_HASHSIZE];
static int cache_defer_cnt;

static int cache_defer_req(struct cache_req *req, struct cache_head *item)
{
        struct cache_deferred_req *dreq;
        int hash = DFR_HASH(item);

        if (cache_defer_cnt >= DFR_MAX) {
                /* too much in the cache, randomly drop this one,
                 * or continue and drop the oldest below
                 */
                if (net_random()&1)
                        return -ETIMEDOUT;
        }
        dreq = req->defer(req);
        if (dreq == NULL)
                return -ETIMEDOUT;

        dreq->item = item;
        dreq->recv_time = get_seconds();

        spin_lock(&cache_defer_lock);

        list_add(&dreq->recent, &cache_defer_list);

        if (cache_defer_hash[hash].next == NULL)
                INIT_LIST_HEAD(&cache_defer_hash[hash]);
        list_add(&dreq->hash, &cache_defer_hash[hash]);

        /* it is in, now maybe clean up */
        dreq = NULL;
        if (++cache_defer_cnt > DFR_MAX) {
                dreq = list_entry(cache_defer_list.prev,
                                  struct cache_deferred_req, recent);
                list_del(&dreq->recent);
                list_del(&dreq->hash);
                cache_defer_cnt--;
        }
        spin_unlock(&cache_defer_lock);

        if (dreq) {
                /* there was one too many */
                dreq->revisit(dreq, 1);
        }
        if (!test_bit(CACHE_PENDING, &item->flags)) {
                /* must have just been validated... */
                cache_revisit_request(item);
        }
        return 0;
}

static void cache_revisit_request(struct cache_head *item)
{
        struct cache_deferred_req *dreq;
        struct list_head pending;

        struct list_head *lp;
        int hash = DFR_HASH(item);

        INIT_LIST_HEAD(&pending);
        spin_lock(&cache_defer_lock);

        lp = cache_defer_hash[hash].next;
        if (lp) {
                while (lp != &cache_defer_hash[hash]) {
                        dreq = list_entry(lp, struct cache_deferred_req, hash);
                        lp = lp->next;
                        if (dreq->item == item) {
                                list_del(&dreq->hash);
                                list_move(&dreq->recent, &pending);
                                cache_defer_cnt--;
                        }
                }
        }
        spin_unlock(&cache_defer_lock);

        while (!list_empty(&pending)) {
                dreq = list_entry(pending.next, struct cache_deferred_req, recent);
                list_del_init(&dreq->recent);
                dreq->revisit(dreq, 0);
        }
}

void cache_clean_deferred(void *owner)
{
        struct cache_deferred_req *dreq, *tmp;
        struct list_head pending;


        INIT_LIST_HEAD(&pending);
        spin_lock(&cache_defer_lock);

        list_for_each_entry_safe(dreq, tmp, &cache_defer_list, recent) {
                if (dreq->owner == owner) {
                        list_del(&dreq->hash);
                        list_move(&dreq->recent, &pending);
                        cache_defer_cnt--;
                }
        }
        spin_unlock(&cache_defer_lock);

        while (!list_empty(&pending)) {
                dreq = list_entry(pending.next, struct cache_deferred_req, recent);
                list_del_init(&dreq->recent);
                dreq->revisit(dreq, 1);
        }
}

/*
 * communicate with user-space
 *
 * We have a magic /proc file - /proc/sunrpc/<cachename>/channel.
 * On read, you get a full request, or block.
 * On write, an update request is processed.
 * Poll works if anything to read, and always allows write.
 *
 * Implemented by linked list of requests.  Each open file has
 * a ->private that also exists in this list.  New requests are added
 * to the end and may wakeup and preceding readers.
 * New readers are added to the head.  If, on read, an item is found with
 * CACHE_UPCALLING clear, we free it from the list.
 *
 */

static DEFINE_SPINLOCK(queue_lock);
static DEFINE_MUTEX(queue_io_mutex);

struct cache_queue {
        struct list_head        list;
        int                     reader; /* if 0, then request */
};
struct cache_request {
        struct cache_queue      q;
        struct cache_head       *item;
        char                    * buf;
        int                     len;
        int                     readers;
};
struct cache_reader {
        struct cache_queue      q;
        int                     offset; /* if non-0, we have a refcnt on next request */
};

static ssize_t
cache_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
        struct cache_reader *rp = filp->private_data;
        struct cache_request *rq;
        struct cache_detail *cd = PDE(filp->f_path.dentry->d_inode)->data;
        int err;

        if (count == 0)
                return 0;

        mutex_lock(&queue_io_mutex); /* protect against multiple concurrent
                              * readers on this file */
 again:
        spin_lock(&queue_lock);
        /* need to find next request */
        while (rp->q.list.next != &cd->queue &&
               list_entry(rp->q.list.next, struct cache_queue, list)
               ->reader) {
                struct list_head *next = rp->q.list.next;
                list_move(&rp->q.list, next);
        }
        if (rp->q.list.next == &cd->queue) {
                spin_unlock(&queue_lock);
                mutex_unlock(&queue_io_mutex);
                BUG_ON(rp->offset);
                return 0;
        }
        rq = container_of(rp->q.list.next, struct cache_request, q.list);
        BUG_ON(rq->q.reader);
        if (rp->offset == 0)
                rq->readers++;
        spin_unlock(&queue_lock);

        if (rp->offset == 0 && !test_bit(CACHE_PENDING, &rq->item->flags)) {
                err = -EAGAIN;
                spin_lock(&queue_lock);
                list_move(&rp->q.list, &rq->q.list);
                spin_unlock(&queue_lock);
        } else {
                if (rp->offset + count > rq->len)
                        count = rq->len - rp->offset;
                err = -EFAULT;
                if (copy_to_user(buf, rq->buf + rp->offset, count))
                        goto out;
                rp->offset += count;
                if (rp->offset >= rq->len) {
                        rp->offset = 0;
                        spin_lock(&queue_lock);
                        list_move(&rp->q.list, &rq->q.list);
                        spin_unlock(&queue_lock);
                }
                err = 0;
        }
 out:
        if (rp->offset == 0) {
                /* need to release rq */
                spin_lock(&queue_lock);
                rq->readers--;
                if (rq->readers == 0 &&
                    !test_bit(CACHE_PENDING, &rq->item->flags)) {
                        list_del(&rq->q.list);
                        spin_unlock(&queue_lock);
                        cache_put(rq->item, cd);
                        kfree(rq->buf);
                        kfree(rq);
                } else
                        spin_unlock(&queue_lock);
        }
        if (err == -EAGAIN)
                goto again;
        mutex_unlock(&queue_io_mutex);
        return err ? err :  count;
}

static char write_buf[8192]; /* protected by queue_io_mutex */

static ssize_t
cache_write(struct file *filp, const char __user *buf, size_t count,
            loff_t *ppos)
{
        int err;
        struct cache_detail *cd = PDE(filp->f_path.dentry->d_inode)->data;

        if (count == 0)
                return 0;
        if (count >= sizeof(write_buf))
                return -EINVAL;

        mutex_lock(&queue_io_mutex);

        if (copy_from_user(write_buf, buf, count)) {
                mutex_unlock(&queue_io_mutex);
                return -EFAULT;
        }
        write_buf[count] = '\0';
        if (cd->cache_parse)
                err = cd->cache_parse(cd, write_buf, count);
        else
                err = -EINVAL;

        mutex_unlock(&queue_io_mutex);
        return err ? err : count;
}

static DECLARE_WAIT_QUEUE_HEAD(queue_wait);

static unsigned int
cache_poll(struct file *filp, poll_table *wait)
{
        unsigned int mask;
        struct cache_reader *rp = filp->private_data;
        struct cache_queue *cq;
        struct cache_detail *cd = PDE(filp->f_path.dentry->d_inode)->data;

        poll_wait(filp, &queue_wait, wait);

        /* alway allow write */
        mask = POLL_OUT | POLLWRNORM;

        if (!rp)
                return mask;

        spin_lock(&queue_lock);

        for (cq= &rp->q; &cq->list != &cd->queue;
             cq = list_entry(cq->list.next, struct cache_queue, list))
                if (!cq->reader) {
                        mask |= POLLIN | POLLRDNORM;
                        break;
                }
        spin_unlock(&queue_lock);
        return mask;
}

static int
cache_ioctl(struct inode *ino, struct file *filp,
            unsigned int cmd, unsigned long arg)
{
        int len = 0;
        struct cache_reader *rp = filp->private_data;
        struct cache_queue *cq;
        struct cache_detail *cd = PDE(ino)->data;

        if (cmd != FIONREAD || !rp)
                return -EINVAL;

        spin_lock(&queue_lock);

        /* only find the length remaining in current request,
         * or the length of the next request
         */
        for (cq= &rp->q; &cq->list != &cd->queue;
             cq = list_entry(cq->list.next, struct cache_queue, list))
                if (!cq->reader) {
                        struct cache_request *cr =
                                container_of(cq, struct cache_request, q);
                        len = cr->len - rp->offset;
                        break;
                }
        spin_unlock(&queue_lock);

        return put_user(len, (int __user *)arg);
}

static int
cache_open(struct inode *inode, struct file *filp)
{
        struct cache_reader *rp = NULL;

        nonseekable_open(inode, filp);
        if (filp->f_mode & FMODE_READ) {
                struct cache_detail *cd = PDE(inode)->data;

                rp = kmalloc(sizeof(*rp), GFP_KERNEL);
                if (!rp)
                        return -ENOMEM;
                rp->offset = 0;
                rp->q.reader = 1;
                atomic_inc(&cd->readers);
                spin_lock(&queue_lock);
                list_add(&rp->q.list, &cd->queue);
                spin_unlock(&queue_lock);
        }
        filp->private_data = rp;
        return 0;
}

static int
cache_release(struct inode *inode, struct file *filp)
{
        struct cache_reader *rp = filp->private_data;
        struct cache_detail *cd = PDE(inode)->data;

        if (rp) {
                spin_lock(&queue_lock);
                if (rp->offset) {
                        struct cache_queue *cq;
                        for (cq= &rp->q; &cq->list != &cd->queue;
                             cq = list_entry(cq->list.next, struct cache_queue, list))
                                if (!cq->reader) {
                                        container_of(cq, struct cache_request, q)
                                                ->readers--;
                                        break;
                                }
                        rp->offset = 0;
                }
                list_del(&rp->q.list);
                spin_unlock(&queue_lock);

                filp->private_data = NULL;
                kfree(rp);

                cd->last_close = get_seconds();
                atomic_dec(&cd->readers);
        }
        return 0;
}



static const struct file_operations cache_file_operations = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .read           = cache_read,
        .write          = cache_write,
        .poll           = cache_poll,
        .ioctl          = cache_ioctl, /* for FIONREAD */
        .open           = cache_open,
        .release        = cache_release,
};


static void queue_loose(struct cache_detail *detail, struct cache_head *ch)
{
        struct cache_queue *cq;
        spin_lock(&queue_lock);
        list_for_each_entry(cq, &detail->queue, list)
                if (!cq->reader) {
                        struct cache_request *cr = container_of(cq, struct cache_request, q);
                        if (cr->item != ch)
                                continue;
                        if (cr->readers != 0)
                                continue;
                        list_del(&cr->q.list);
                        spin_unlock(&queue_lock);
                        cache_put(cr->item, detail);
                        kfree(cr->buf);
                        kfree(cr);
                        return;
                }
        spin_unlock(&queue_lock);
}

/*
 * Support routines for text-based upcalls.
 * Fields are separated by spaces.
 * Fields are either mangled to quote space tab newline slosh with slosh
 * or a hexified with a leading \x
 * Record is terminated with newline.
 *
 */

void qword_add(char **bpp, int *lp, char *str)
{
        char *bp = *bpp;
        int len = *lp;
        char c;

        if (len < 0) return;

        while ((c=*str++) && len)
                switch(c) {
                case ' ':
                case '\t':
                case '\n':
                case '\\':
                        if (len >= 4) {
                                *bp++ = '\\';
                                *bp++ = '0' + ((c & 0300)>>6);
                                *bp++ = '0' + ((c & 0070)>>3);
                                *bp++ = '0' + ((c & 0007)>>0);
                        }
                        len -= 4;
                        break;
                default:
                        *bp++ = c;
                        len--;
                }
        if (c || len <1) len = -1;
        else {
                *bp++ = ' ';
                len--;
        }
        *bpp = bp;
        *lp = len;
}

void qword_addhex(char **bpp, int *lp, char *buf, int blen)
{
        char *bp = *bpp;
        int len = *lp;

        if (len < 0) return;

        if (len > 2) {
                *bp++ = '\\';
                *bp++ = 'x';
                len -= 2;
                while (blen && len >= 2) {
                        unsigned char c = *buf++;
                        *bp++ = '0' + ((c&0xf0)>>4) + (c>=0xa0)*('a'-'9'-1);
                        *bp++ = '0' + (c&0x0f) + ((c&0x0f)>=0x0a)*('a'-'9'-1);
                        len -= 2;
                        blen--;
                }
        }
        if (blen || len<1) len = -1;
        else {
                *bp++ = ' ';
                len--;
        }
        *bpp = bp;
        *lp = len;
}

static void warn_no_listener(struct cache_detail *detail)
{
        if (detail->last_warn != detail->last_close) {
                detail->last_warn = detail->last_close;
                if (detail->warn_no_listener)
                        detail->warn_no_listener(detail);
        }
}

/*
 * register an upcall request to user-space.
 * Each request is at most one page long.
 */
static int cache_make_upcall(struct cache_detail *detail, struct cache_head *h)
{

        char *buf;
        struct cache_request *crq;
        char *bp;
        int len;

        if (detail->cache_request == NULL)
                return -EINVAL;

        if (atomic_read(&detail->readers) == 0 &&
            detail->last_close < get_seconds() - 30) {
                        warn_no_listener(detail);
                        return -EINVAL;
        }

        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!buf)
                return -EAGAIN;

        crq = kmalloc(sizeof (*crq), GFP_KERNEL);
        if (!crq) {
                kfree(buf);
                return -EAGAIN;
        }

        bp = buf; len = PAGE_SIZE;

        detail->cache_request(detail, h, &bp, &len);

        if (len < 0) {
                kfree(buf);
                kfree(crq);
                return -EAGAIN;
        }
        crq->q.reader = 0;
        crq->item = cache_get(h);
        crq->buf = buf;
        crq->len = PAGE_SIZE - len;
        crq->readers = 0;
        spin_lock(&queue_lock);
        list_add_tail(&crq->q.list, &detail->queue);
        spin_unlock(&queue_lock);
        wake_up(&queue_wait);
        return 0;
}

/*
 * parse a message from user-space and pass it
 * to an appropriate cache
 * Messages are, like requests, separated into fields by
 * spaces and dequotes as \xHEXSTRING or embedded \nnn octal
 *
 * Message is
 *   reply cachename expiry key ... content....
 *
 * key and content are both parsed by cache
 */

#define isodigit(c) (isdigit(c) && c <= '7')
int qword_get(char **bpp, char *dest, int bufsize)
{
        /* return bytes copied, or -1 on error */
        char *bp = *bpp;
        int len = 0;

        while (*bp == ' ') bp++;

        if (bp[0] == '\\' && bp[1] == 'x') {
                /* HEX STRING */
                bp += 2;
                while (isxdigit(bp[0]) && isxdigit(bp[1]) && len < bufsize) {
                        int byte = isdigit(*bp) ? *bp-'0' : toupper(*bp)-'A'+10;
                        bp++;
                        byte <<= 4;
                        byte |= isdigit(*bp) ? *bp-'0' : toupper(*bp)-'A'+10;
                        *dest++ = byte;
                        bp++;
                        len++;
                }
        } else {
                /* text with \nnn octal quoting */
                while (*bp != ' ' && *bp != '\n' && *bp && len < bufsize-1) {
                        if (*bp == '\\' &&
                            isodigit(bp[1]) && (bp[1] <= '3') &&
                            isodigit(bp[2]) &&
                            isodigit(bp[3])) {
                                int byte = (*++bp -'0');
                                bp++;
                                byte = (byte << 3) | (*bp++ - '0');
                                byte = (byte << 3) | (*bp++ - '0');
                                *dest++ = byte;
                                len++;
                        } else {
                                *dest++ = *bp++;
                                len++;
                        }
                }
        }

        if (*bp != ' ' && *bp != '\n' && *bp != '\0')
                return -1;
        while (*bp == ' ') bp++;
        *bpp = bp;
        *dest = '\0';
        return len;
}


/*
 * support /proc/sunrpc/cache/$CACHENAME/content
 * as a seqfile.
 * We call ->cache_show passing NULL for the item to
 * get a header, then pass each real item in the cache
 */

struct handle {
        struct cache_detail *cd;
};

static void *c_start(struct seq_file *m, loff_t *pos)
        __acquires(cd->hash_lock)
{
        loff_t n = *pos;
        unsigned hash, entry;
        struct cache_head *ch;
        struct cache_detail *cd = ((struct handle*)m->private)->cd;


        read_lock(&cd->hash_lock);
        if (!n--)
                return SEQ_START_TOKEN;
        hash = n >> 32;
        entry = n & ((1LL<<32) - 1);

        for (ch=cd->hash_table[hash]; ch; ch=ch->next)
                if (!entry--)
                        return ch;
        n &= ~((1LL<<32) - 1);
        do {
                hash++;
                n += 1LL<<32;
        } while(hash < cd->hash_size &&
                cd->hash_table[hash]==NULL);
        if (hash >= cd->hash_size)
                return NULL;
        *pos = n+1;
        return cd->hash_table[hash];
}

static void *c_next(struct seq_file *m, void *p, loff_t *pos)
{
        struct cache_head *ch = p;
        int hash = (*pos >> 32);
        struct cache_detail *cd = ((struct handle*)m->private)->cd;

        if (p == SEQ_START_TOKEN)
                hash = 0;
        else if (ch->next == NULL) {
                hash++;
                *pos += 1LL<<32;
        } else {
                ++*pos;
                return ch->next;
        }
        *pos &= ~((1LL<<32) - 1);
        while (hash < cd->hash_size &&
               cd->hash_table[hash] == NULL) {
                hash++;
                *pos += 1LL<<32;
        }
        if (hash >= cd->hash_size)
                return NULL;
        ++*pos;
        return cd->hash_table[hash];
}

static void c_stop(struct seq_file *m, void *p)
        __releases(cd->hash_lock)
{
        struct cache_detail *cd = ((struct handle*)m->private)->cd;
        read_unlock(&cd->hash_lock);
}

static int c_show(struct seq_file *m, void *p)
{
        struct cache_head *cp = p;
        struct cache_detail *cd = ((struct handle*)m->private)->cd;

        if (p == SEQ_START_TOKEN)
                return cd->cache_show(m, cd, NULL);

        ifdebug(CACHE)
                seq_printf(m, "# expiry=%ld refcnt=%d flags=%lx\n",
                           cp->expiry_time, atomic_read(&cp->ref.refcount), cp->flags);
        cache_get(cp);
        if (cache_check(cd, cp, NULL))
                /* cache_check does a cache_put on failure */
                seq_printf(m, "# ");
        else
                cache_put(cp, cd);

        return cd->cache_show(m, cd, cp);
}

static const struct seq_operations cache_content_op = {
        .start  = c_start,
        .next   = c_next,
        .stop   = c_stop,
        .show   = c_show,
};

static int content_open(struct inode *inode, struct file *file)
{
        struct handle *han;
        struct cache_detail *cd = PDE(inode)->data;

        han = __seq_open_private(file, &cache_content_op, sizeof(*han));
        if (han == NULL)
                return -ENOMEM;

        han->cd = cd;
        return 0;
}

static const struct file_operations content_file_operations = {
        .open           = content_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release_private,
};

static ssize_t read_flush(struct file *file, char __user *buf,
                            size_t count, loff_t *ppos)
{
        struct cache_detail *cd = PDE(file->f_path.dentry->d_inode)->data;
        char tbuf[20];
        unsigned long p = *ppos;
        size_t len;

        sprintf(tbuf, "%lu\n", cd->flush_time);
        len = strlen(tbuf);
        if (p >= len)
                return 0;
        len -= p;
        if (len > count)
                len = count;
        if (copy_to_user(buf, (void*)(tbuf+p), len))
                return -EFAULT;
        *ppos += len;
        return len;
}

static ssize_t write_flush(struct file * file, const char __user * buf,
                             size_t count, loff_t *ppos)
{
        struct cache_detail *cd = PDE(file->f_path.dentry->d_inode)->data;
        char tbuf[20];
        char *ep;
        long flushtime;
        if (*ppos || count > sizeof(tbuf)-1)
                return -EINVAL;
        if (copy_from_user(tbuf, buf, count))
                return -EFAULT;
        tbuf[count] = 0;
        flushtime = simple_strtoul(tbuf, &ep, 0);
        if (*ep && *ep != '\n')
                return -EINVAL;

        cd->flush_time = flushtime;
        cd->nextcheck = get_seconds();
        cache_flush();

        *ppos += count;
        return count;
}

static const struct file_operations cache_flush_operations = {
        .open           = nonseekable_open,
        .read           = read_flush,
        .write          = write_flush,
};