text: /*
   * 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/slab.h>
  
  #include "nfsd.h"
  #include "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;
  }
  