/*
 * linux/fs/nfsd/nfscache.c
 *
 * Request reply cache. This is currently a global cache, but this may
 * change in the future and be a per-client cache.
 *
 * This code is heavily inspired by the 44BSD implementation, although
 * it does things a bit differently.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/kernel.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/list.h>

#include <linux/sunrpc/svc.h>
#include <linux/nfsd/nfsd.h>
#include <linux/nfsd/cache.h>

/* Size of reply cache. Common values are:
 * 4.3BSD:      128
 * 4.4BSD:      256
 * Solaris2:    1024
 * DEC Unix:    512-4096
 */
#define CACHESIZE               1024
#define HASHSIZE                64

static struct hlist_head *      cache_hash;
static struct list_head         lru_head;
static int                      cache_disabled = 1;

/*
 * Calculate the hash index from an XID.
 */
static inline u32 request_hash(u32 xid)
{
        u32 h = xid;
        h ^= (xid >> 24);
        return h & (HASHSIZE-1);
}

static int      nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);

/*
 * locking for the reply cache:
 * A cache entry is "single use" if c_state == RC_INPROG
 * Otherwise, it when accessing _prev or _next, the lock must be held.
 */
static DEFINE_SPINLOCK(cache_lock);

int nfsd_reply_cache_init(void)
{
        struct svc_cacherep     *rp;
        int                     i;

        INIT_LIST_HEAD(&lru_head);
        i = CACHESIZE;
        while (i) {
                rp = kmalloc(sizeof(*rp), GFP_KERNEL);
                if (!rp)
                        goto out_nomem;
                list_add(&rp->c_lru, &lru_head);
                rp->c_state = RC_UNUSED;
                rp->c_type = RC_NOCACHE;
                INIT_HLIST_NODE(&rp->c_hash);
                i--;
        }

        cache_hash = kcalloc (HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
        if (!cache_hash)
                goto out_nomem;

        cache_disabled = 0;
        return 0;
out_nomem:
        printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
        nfsd_reply_cache_shutdown();
        return -ENOMEM;
}

void nfsd_reply_cache_shutdown(void)
{
        struct svc_cacherep     *rp;

        while (!list_empty(&lru_head)) {
                rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
                if (rp->c_state == RC_DONE && rp->c_type == RC_REPLBUFF)
                        kfree(rp->c_replvec.iov_base);
                list_del(&rp->c_lru);
                kfree(rp);
        }

        cache_disabled = 1;

        kfree (cache_hash);
        cache_hash = NULL;
}

/*
 * Move cache entry to end of LRU list
 */
static void
lru_put_end(struct svc_cacherep *rp)
{
        list_move_tail(&rp->c_lru, &lru_head);
}

/*
 * Move a cache entry from one hash list to another
 */
static void
hash_refile(struct svc_cacherep *rp)
{
        hlist_del_init(&rp->c_hash);
        hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
}

/*
 * Try to find an entry matching the current call in the cache. When none
 * is found, we grab the oldest unlocked entry off the LRU list.
 * Note that no operation within the loop may sleep.
 */
int
nfsd_cache_lookup(struct svc_rqst *rqstp, int type)
{
        struct hlist_node       *hn;
        struct hlist_head       *rh;
        struct svc_cacherep     *rp;
        __be32                  xid = rqstp->rq_xid;
        u32                     proto =  rqstp->rq_prot,
                                vers = rqstp->rq_vers,
                                proc = rqstp->rq_proc;
        unsigned long           age;
        int rtn;

        rqstp->rq_cacherep = NULL;
        if (cache_disabled || type == RC_NOCACHE) {
                nfsdstats.rcnocache++;
                return RC_DOIT;
        }

        spin_lock(&cache_lock);
        rtn = RC_DOIT;

        rh = &cache_hash[request_hash(xid)];
        hlist_for_each_entry(rp, hn, rh, c_hash) {
                if (rp->c_state != RC_UNUSED &&
                    xid == rp->c_xid && proc == rp->c_proc &&
                    proto == rp->c_prot && vers == rp->c_vers &&
                    time_before(jiffies, rp->c_timestamp + 120*HZ) &&
                    memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
                        nfsdstats.rchits++;
                        goto found_entry;
                }
        }
        nfsdstats.rcmisses++;

        /* This loop shouldn't take more than a few iterations normally */
        {
        int     safe = 0;
        list_for_each_entry(rp, &lru_head, c_lru) {
                if (rp->c_state != RC_INPROG)
                        break;
                if (safe++ > CACHESIZE) {
                        printk("nfsd: loop in repcache LRU list\n");
                        cache_disabled = 1;
                        goto out;
                }
        }
        }

        /* All entries on the LRU are in-progress. This should not happen */
        if (&rp->c_lru == &lru_head) {
                static int      complaints;

                printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
                if (++complaints > 5) {
                        printk(KERN_WARNING "nfsd: disabling repcache.\n");
                        cache_disabled = 1;
                }
                goto out;
        }

        rqstp->rq_cacherep = rp;
        rp->c_state = RC_INPROG;
        rp->c_xid = xid;
        rp->c_proc = proc;
        memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
        rp->c_prot = proto;
        rp->c_vers = vers;
        rp->c_timestamp = jiffies;

        hash_refile(rp);

        /* release any buffer */
        if (rp->c_type == RC_REPLBUFF) {
                kfree(rp->c_replvec.iov_base);
                rp->c_replvec.iov_base = NULL;
        }
        rp->c_type = RC_NOCACHE;
 out:
        spin_unlock(&cache_lock);
        return rtn;

found_entry:
        /* We found a matching entry which is either in progress or done. */
        age = jiffies - rp->c_timestamp;
        rp->c_timestamp = jiffies;
        lru_put_end(rp);

        rtn = RC_DROPIT;
        /* Request being processed or excessive rexmits */
        if (rp->c_state == RC_INPROG || age < RC_DELAY)
                goto out;

        /* From the hall of fame of impractical attacks:
         * Is this a user who tries to snoop on the cache? */
        rtn = RC_DOIT;
        if (!rqstp->rq_secure && rp->c_secure)
                goto out;

        /* Compose RPC reply header */
        switch (rp->c_type) {
        case RC_NOCACHE:
                break;
        case RC_REPLSTAT:
                svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
                rtn = RC_REPLY;
                break;
        case RC_REPLBUFF:
                if (!nfsd_cache_append(rqstp, &rp->c_replvec))
                        goto out;       /* should not happen */
                rtn = RC_REPLY;
                break;
        default:
                printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
                rp->c_state = RC_UNUSED;
        }

        goto out;
}

/*
 * Update a cache entry. This is called from nfsd_dispatch when
 * the procedure has been executed and the complete reply is in
 * rqstp->rq_res.
 *
 * We're copying around data here rather than swapping buffers because
 * the toplevel loop requires max-sized buffers, which would be a waste
 * of memory for a cache with a max reply size of 100 bytes (diropokres).
 *
 * If we should start to use different types of cache entries tailored
 * specifically for attrstat and fh's, we may save even more space.
 *
 * Also note that a cachetype of RC_NOCACHE can legally be passed when
 * nfsd failed to encode a reply that otherwise would have been cached.
 * In this case, nfsd_cache_update is called with statp == NULL.
 */
void
nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
{
        struct svc_cacherep *rp;
        struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
        int             len;

        if (!(rp = rqstp->rq_cacherep) || cache_disabled)
                return;

        len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
        len >>= 2;

        /* Don't cache excessive amounts of data and XDR failures */
        if (!statp || len > (256 >> 2)) {
                rp->c_state = RC_UNUSED;
                return;
        }

        switch (cachetype) {
        case RC_REPLSTAT:
                if (len != 1)
                        printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
                rp->c_replstat = *statp;
                break;
        case RC_REPLBUFF:
                cachv = &rp->c_replvec;
                cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
                if (!cachv->iov_base) {
                        spin_lock(&cache_lock);
                        rp->c_state = RC_UNUSED;
                        spin_unlock(&cache_lock);
                        return;
                }
                cachv->iov_len = len << 2;
                memcpy(cachv->iov_base, statp, len << 2);
                break;
        }
        spin_lock(&cache_lock);
        lru_put_end(rp);
        rp->c_secure = rqstp->rq_secure;
        rp->c_type = cachetype;
        rp->c_state = RC_DONE;
        rp->c_timestamp = jiffies;
        spin_unlock(&cache_lock);
        return;
}

/*
 * Copy cached reply to current reply buffer. Should always fit.
 * FIXME as reply is in a page, we should just attach the page, and
 * keep a refcount....
 */
static int
nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
{
        struct kvec     *vec = &rqstp->rq_res.head[0];

        if (vec->iov_len + data->iov_len > PAGE_SIZE) {
                printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
                                data->iov_len);
                return 0;
        }
        memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
        vec->iov_len += data->iov_len;
        return 1;
}