fs/nfsd/nfscache.c - kernel/msm-4.9 - Gitiles

 /*
  * 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 <linux/sunrpc/addr.h>
 #include <linux/highmem.h>
 #include <net/checksum.h>

 #include "nfsd.h"
 #include "cache.h"

 #define NFSDDBG_FACILITY	NFSDDBG_REPCACHE

 #define HASHSIZE		64

 static struct hlist_head *	cache_hash;
 static struct list_head 	lru_head;
 static struct kmem_cache	*drc_slab;
 static unsigned int		num_drc_entries;
 static unsigned int		max_drc_entries;

 /*
  * 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);
 static void	cache_cleaner_func(struct work_struct *unused);
 static int 	nfsd_reply_cache_shrink(struct shrinker *shrink,
 					struct shrink_control *sc);

 struct shrinker nfsd_reply_cache_shrinker = {
 	.shrink	= nfsd_reply_cache_shrink,
 	.seeks	= 1,
 };

 /*
  * 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);
 static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func);

 /*
  * Put a cap on the size of the DRC based on the amount of available
  * low memory in the machine.
  *
  *  64MB:    8192
  * 128MB:   11585
  * 256MB:   16384
  * 512MB:   23170
  *   1GB:   32768
  *   2GB:   46340
  *   4GB:   65536
  *   8GB:   92681
  *  16GB:  131072
  *
  * ...with a hard cap of 256k entries. In the worst case, each entry will be
  * ~1k, so the above numbers should give a rough max of the amount of memory
  * used in k.
  */
 static unsigned int
 nfsd_cache_size_limit(void)
 {
 	unsigned int limit;
 	unsigned long low_pages = totalram_pages - totalhigh_pages;

 	limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
 	return min_t(unsigned int, limit, 256*1024);
 }

 static struct svc_cacherep *
 nfsd_reply_cache_alloc(void)
 {
 	struct svc_cacherep	*rp;

 	rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
 	if (rp) {
 		rp->c_state = RC_UNUSED;
 		rp->c_type = RC_NOCACHE;
 		INIT_LIST_HEAD(&rp->c_lru);
 		INIT_HLIST_NODE(&rp->c_hash);
 	}
 	return rp;
 }

 static void
 nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
 {
 	if (rp->c_type == RC_REPLBUFF)
 		kfree(rp->c_replvec.iov_base);
 	if (!hlist_unhashed(&rp->c_hash))
 		hlist_del(&rp->c_hash);
 	list_del(&rp->c_lru);
 	--num_drc_entries;
 	kmem_cache_free(drc_slab, rp);
 }

 static void
 nfsd_reply_cache_free(struct svc_cacherep *rp)
 {
 	spin_lock(&cache_lock);
 	nfsd_reply_cache_free_locked(rp);
 	spin_unlock(&cache_lock);
 }

 int nfsd_reply_cache_init(void)
 {
 	INIT_LIST_HEAD(&lru_head);
 	max_drc_entries = nfsd_cache_size_limit();
 	num_drc_entries = 0;

 	register_shrinker(&nfsd_reply_cache_shrinker);
 	drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
 					0, 0, NULL);
 	if (!drc_slab)
 		goto out_nomem;

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

 	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;

 	unregister_shrinker(&nfsd_reply_cache_shrinker);
 	cancel_delayed_work_sync(&cache_cleaner);

 	while (!list_empty(&lru_head)) {
 		rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
 		nfsd_reply_cache_free_locked(rp);
 	}

 	kfree (cache_hash);
 	cache_hash = NULL;

 	if (drc_slab) {
 		kmem_cache_destroy(drc_slab);
 		drc_slab = NULL;
 	}
 }

 /*
  * Move cache entry to end of LRU list, and queue the cleaner to run if it's
  * not already scheduled.
  */
 static void
 lru_put_end(struct svc_cacherep *rp)
 {
 	rp->c_timestamp = jiffies;
 	list_move_tail(&rp->c_lru, &lru_head);
 	schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
 }

 /*
  * 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));
 }

 static inline bool
 nfsd_cache_entry_expired(struct svc_cacherep *rp)
 {
 	return rp->c_state != RC_INPROG &&
 	       time_after(jiffies, rp->c_timestamp + RC_EXPIRE);
 }

 /*
  * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
  * Also prune the oldest ones when the total exceeds the max number of entries.
  */
 static void
 prune_cache_entries(void)
 {
 	struct svc_cacherep *rp, *tmp;

 	list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) {
 		if (!nfsd_cache_entry_expired(rp) &&
 		    num_drc_entries <= max_drc_entries)
 			break;
 		nfsd_reply_cache_free_locked(rp);
 	}

 	/*
 	 * Conditionally rearm the job. If we cleaned out the list, then
 	 * cancel any pending run (since there won't be any work to do).
 	 * Otherwise, we rearm the job or modify the existing one to run in
 	 * RC_EXPIRE since we just ran the pruner.
 	 */
 	if (list_empty(&lru_head))
 		cancel_delayed_work(&cache_cleaner);
 	else
 		mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
 }

 static void
 cache_cleaner_func(struct work_struct *unused)
 {
 	spin_lock(&cache_lock);
 	prune_cache_entries();
 	spin_unlock(&cache_lock);
 }

 static int
 nfsd_reply_cache_shrink(struct shrinker *shrink, struct shrink_control *sc)
 {
 	unsigned int num;

 	spin_lock(&cache_lock);
 	if (sc->nr_to_scan)
 		prune_cache_entries();
 	num = num_drc_entries;
 	spin_unlock(&cache_lock);

 	return num;
 }

 /*
  * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
  */
 static __wsum
 nfsd_cache_csum(struct svc_rqst *rqstp)
 {
 	int idx;
 	unsigned int base;
 	__wsum csum;
 	struct xdr_buf *buf = &rqstp->rq_arg;
 	const unsigned char *p = buf->head[0].iov_base;
 	size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
 				RC_CSUMLEN);
 	size_t len = min(buf->head[0].iov_len, csum_len);

 	/* rq_arg.head first */
 	csum = csum_partial(p, len, 0);
 	csum_len -= len;

 	/* Continue into page array */
 	idx = buf->page_base / PAGE_SIZE;
 	base = buf->page_base & ~PAGE_MASK;
 	while (csum_len) {
 		p = page_address(buf->pages[idx]) + base;
 		len = min_t(size_t, PAGE_SIZE - base, csum_len);
 		csum = csum_partial(p, len, csum);
 		csum_len -= len;
 		base = 0;
 		++idx;
 	}
 	return csum;
 }

 /*
  * Search the request hash for an entry that matches the given rqstp.
  * Must be called with cache_lock held. Returns the found entry or
  * NULL on failure.
  */
 static struct svc_cacherep *
 nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum)
 {
 	struct svc_cacherep	*rp;
 	struct hlist_head 	*rh;
 	__be32			xid = rqstp->rq_xid;
 	u32			proto =  rqstp->rq_prot,
 				vers = rqstp->rq_vers,
 				proc = rqstp->rq_proc;

 	rh = &cache_hash[request_hash(xid)];
 	hlist_for_each_entry(rp, rh, c_hash) {
 		if (xid == rp->c_xid && proc == rp->c_proc &&
 		    proto == rp->c_prot && vers == rp->c_vers &&
 		    rqstp->rq_arg.len == rp->c_len && csum == rp->c_csum &&
 		    rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) &&
 		    rpc_get_port(svc_addr(rqstp)) == rpc_get_port((struct sockaddr *)&rp->c_addr))
 			return rp;
 	}
 	return NULL;
 }

 /*
  * Try to find an entry matching the current call in the cache. When none
  * is found, we try to grab the oldest expired entry off the LRU list. If
  * a suitable one isn't there, then drop the cache_lock and allocate a
  * new one, then search again in case one got inserted while this thread
  * didn't hold the lock.
  */
 int
 nfsd_cache_lookup(struct svc_rqst *rqstp)
 {
 	struct svc_cacherep	*rp, *found;
 	__be32			xid = rqstp->rq_xid;
 	u32			proto =  rqstp->rq_prot,
 				vers = rqstp->rq_vers,
 				proc = rqstp->rq_proc;
 	__wsum			csum;
 	unsigned long		age;
 	int type = rqstp->rq_cachetype;
 	int rtn;

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

 	csum = nfsd_cache_csum(rqstp);

 	spin_lock(&cache_lock);
 	rtn = RC_DOIT;

 	rp = nfsd_cache_search(rqstp, csum);
 	if (rp)
 		goto found_entry;

 	/* Try to use the first entry on the LRU */
 	if (!list_empty(&lru_head)) {
 		rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
 		if (nfsd_cache_entry_expired(rp) ||
 		    num_drc_entries >= max_drc_entries) {
 			lru_put_end(rp);
 			prune_cache_entries();
 			goto setup_entry;
 		}
 	}

 	/* Drop the lock and allocate a new entry */
 	spin_unlock(&cache_lock);
 	rp = nfsd_reply_cache_alloc();
 	if (!rp) {
 		dprintk("nfsd: unable to allocate DRC entry!\n");
 		return RC_DOIT;
 	}
 	spin_lock(&cache_lock);
 	++num_drc_entries;

 	/*
 	 * Must search again just in case someone inserted one
 	 * after we dropped the lock above.
 	 */
 	found = nfsd_cache_search(rqstp, csum);
 	if (found) {
 		nfsd_reply_cache_free_locked(rp);
 		rp = found;
 		goto found_entry;
 	}

 	/*
 	 * We're keeping the one we just allocated. Are we now over the
 	 * limit? Prune one off the tip of the LRU in trade for the one we
 	 * just allocated if so.
 	 */
 	if (num_drc_entries >= max_drc_entries)
 		nfsd_reply_cache_free_locked(list_first_entry(&lru_head,
 						struct svc_cacherep, c_lru));

 setup_entry:
 	nfsdstats.rcmisses++;
 	rqstp->rq_cacherep = rp;
 	rp->c_state = RC_INPROG;
 	rp->c_xid = xid;
 	rp->c_proc = proc;
 	rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
 	rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
 	rp->c_prot = proto;
 	rp->c_vers = vers;
 	rp->c_len = rqstp->rq_arg.len;
 	rp->c_csum = csum;

 	hash_refile(rp);
 	lru_put_end(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:
 	nfsdstats.rchits++;
 	/* We found a matching entry which is either in progress or done. */
 	age = jiffies - rp->c_timestamp;
 	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);
 		nfsd_reply_cache_free_locked(rp);
 	}

 	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 = rqstp->rq_cacherep;
 	struct kvec	*resv = &rqstp->rq_res.head[0], *cachv;
 	int		len;

 	if (!rp)
 		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)) {
 		nfsd_reply_cache_free(rp);
 		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) {
 			nfsd_reply_cache_free(rp);
 			return;
 		}
 		cachv->iov_len = len << 2;
 		memcpy(cachv->iov_base, statp, len << 2);
 		break;
 	case RC_NOCACHE:
 		nfsd_reply_cache_free(rp);
 		return;
 	}
 	spin_lock(&cache_lock);
 	lru_put_end(rp);
 	rp->c_secure = rqstp->rq_secure;
 	rp->c_type = cachetype;
 	rp->c_state = RC_DONE;
 	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;
 }
	/*
	* 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 <linux/sunrpc/addr.h>
	#include <linux/highmem.h>
	#include <net/checksum.h>

	#include "nfsd.h"
	#include "cache.h"

	#define NFSDDBG_FACILITY NFSDDBG_REPCACHE

	#define HASHSIZE 64

	static struct hlist_head * cache_hash;
	static struct list_head lru_head;
	static struct kmem_cache *drc_slab;
	static unsigned int num_drc_entries;
	static unsigned int max_drc_entries;

	/*
	* 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);
	static void cache_cleaner_func(struct work_struct *unused);
	static int nfsd_reply_cache_shrink(struct shrinker *shrink,
	struct shrink_control *sc);

	struct shrinker nfsd_reply_cache_shrinker = {
	.shrink = nfsd_reply_cache_shrink,
	.seeks = 1,
	};

	/*
	* 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);
	static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func);

	/*
	* Put a cap on the size of the DRC based on the amount of available
	* low memory in the machine.
	*
	* 64MB: 8192
	* 128MB: 11585
	* 256MB: 16384
	* 512MB: 23170
	* 1GB: 32768
	* 2GB: 46340
	* 4GB: 65536
	* 8GB: 92681
	* 16GB: 131072
	*
	* ...with a hard cap of 256k entries. In the worst case, each entry will be
	* ~1k, so the above numbers should give a rough max of the amount of memory
	* used in k.
	*/
	static unsigned int
	nfsd_cache_size_limit(void)
	{
	unsigned int limit;
	unsigned long low_pages = totalram_pages - totalhigh_pages;

	limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
	return min_t(unsigned int, limit, 256*1024);
	}

	static struct svc_cacherep *
	nfsd_reply_cache_alloc(void)
	{
	struct svc_cacherep *rp;

	rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
	if (rp) {
	rp->c_state = RC_UNUSED;
	rp->c_type = RC_NOCACHE;
	INIT_LIST_HEAD(&rp->c_lru);
	INIT_HLIST_NODE(&rp->c_hash);
	}
	return rp;
	}

	static void
	nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
	{
	if (rp->c_type == RC_REPLBUFF)
	kfree(rp->c_replvec.iov_base);
	if (!hlist_unhashed(&rp->c_hash))
	hlist_del(&rp->c_hash);
	list_del(&rp->c_lru);
	--num_drc_entries;
	kmem_cache_free(drc_slab, rp);
	}

	static void
	nfsd_reply_cache_free(struct svc_cacherep *rp)
	{
	spin_lock(&cache_lock);
	nfsd_reply_cache_free_locked(rp);
	spin_unlock(&cache_lock);
	}

	int nfsd_reply_cache_init(void)
	{
	INIT_LIST_HEAD(&lru_head);
	max_drc_entries = nfsd_cache_size_limit();
	num_drc_entries = 0;

	register_shrinker(&nfsd_reply_cache_shrinker);
	drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
	0, 0, NULL);
	if (!drc_slab)
	goto out_nomem;

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

	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;

	unregister_shrinker(&nfsd_reply_cache_shrinker);
	cancel_delayed_work_sync(&cache_cleaner);

	while (!list_empty(&lru_head)) {
	rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
	nfsd_reply_cache_free_locked(rp);
	}

	kfree (cache_hash);
	cache_hash = NULL;

	if (drc_slab) {
	kmem_cache_destroy(drc_slab);
	drc_slab = NULL;
	}
	}

	/*
	* Move cache entry to end of LRU list, and queue the cleaner to run if it's
	* not already scheduled.
	*/
	static void
	lru_put_end(struct svc_cacherep *rp)
	{
	rp->c_timestamp = jiffies;
	list_move_tail(&rp->c_lru, &lru_head);
	schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
	}

	/*
	* 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));
	}

	static inline bool
	nfsd_cache_entry_expired(struct svc_cacherep *rp)
	{
	return rp->c_state != RC_INPROG &&
	time_after(jiffies, rp->c_timestamp + RC_EXPIRE);
	}

	/*
	* Walk the LRU list and prune off entries that are older than RC_EXPIRE.
	* Also prune the oldest ones when the total exceeds the max number of entries.
	*/
	static void
	prune_cache_entries(void)
	{
	struct svc_cacherep rp, tmp;

	list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) {
	if (!nfsd_cache_entry_expired(rp) &&
	num_drc_entries <= max_drc_entries)
	break;
	nfsd_reply_cache_free_locked(rp);
	}

	/*
	* Conditionally rearm the job. If we cleaned out the list, then
	* cancel any pending run (since there won't be any work to do).
	* Otherwise, we rearm the job or modify the existing one to run in
	* RC_EXPIRE since we just ran the pruner.
	*/
	if (list_empty(&lru_head))
	cancel_delayed_work(&cache_cleaner);
	else
	mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
	}

	static void
	cache_cleaner_func(struct work_struct *unused)
	{
	spin_lock(&cache_lock);
	prune_cache_entries();
	spin_unlock(&cache_lock);
	}

	static int
	nfsd_reply_cache_shrink(struct shrinker shrink, struct shrink_control sc)
	{
	unsigned int num;

	spin_lock(&cache_lock);
	if (sc->nr_to_scan)
	prune_cache_entries();
	num = num_drc_entries;
	spin_unlock(&cache_lock);

	return num;
	}

	/*
	* Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
	*/
	static __wsum
	nfsd_cache_csum(struct svc_rqst *rqstp)
	{
	int idx;
	unsigned int base;
	__wsum csum;
	struct xdr_buf *buf = &rqstp->rq_arg;
	const unsigned char *p = buf->head[0].iov_base;
	size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
	RC_CSUMLEN);
	size_t len = min(buf->head[0].iov_len, csum_len);

	/* rq_arg.head first */
	csum = csum_partial(p, len, 0);
	csum_len -= len;

	/* Continue into page array */
	idx = buf->page_base / PAGE_SIZE;
	base = buf->page_base & ~PAGE_MASK;
	while (csum_len) {
	p = page_address(buf->pages[idx]) + base;
	len = min_t(size_t, PAGE_SIZE - base, csum_len);
	csum = csum_partial(p, len, csum);
	csum_len -= len;
	base = 0;
	++idx;
	}
	return csum;
	}

	/*
	* Search the request hash for an entry that matches the given rqstp.
	* Must be called with cache_lock held. Returns the found entry or
	* NULL on failure.
	*/
	static struct svc_cacherep *
	nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum)
	{
	struct svc_cacherep *rp;
	struct hlist_head *rh;
	__be32 xid = rqstp->rq_xid;
	u32 proto = rqstp->rq_prot,
	vers = rqstp->rq_vers,
	proc = rqstp->rq_proc;

	rh = &cache_hash[request_hash(xid)];
	hlist_for_each_entry(rp, rh, c_hash) {
	if (xid == rp->c_xid && proc == rp->c_proc &&
	proto == rp->c_prot && vers == rp->c_vers &&
	rqstp->rq_arg.len == rp->c_len && csum == rp->c_csum &&
	rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) &&
	rpc_get_port(svc_addr(rqstp)) == rpc_get_port((struct sockaddr *)&rp->c_addr))
	return rp;
	}
	return NULL;
	}

	/*
	* Try to find an entry matching the current call in the cache. When none
	* is found, we try to grab the oldest expired entry off the LRU list. If
	* a suitable one isn't there, then drop the cache_lock and allocate a
	* new one, then search again in case one got inserted while this thread
	* didn't hold the lock.
	*/
	int
	nfsd_cache_lookup(struct svc_rqst *rqstp)
	{
	struct svc_cacherep rp, found;
	__be32 xid = rqstp->rq_xid;
	u32 proto = rqstp->rq_prot,
	vers = rqstp->rq_vers,
	proc = rqstp->rq_proc;
	__wsum csum;
	unsigned long age;
	int type = rqstp->rq_cachetype;
	int rtn;

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

	csum = nfsd_cache_csum(rqstp);

	spin_lock(&cache_lock);
	rtn = RC_DOIT;

	rp = nfsd_cache_search(rqstp, csum);
	if (rp)
	goto found_entry;

	/* Try to use the first entry on the LRU */
	if (!list_empty(&lru_head)) {
	rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
	if (nfsd_cache_entry_expired(rp) \|\|
	num_drc_entries >= max_drc_entries) {
	lru_put_end(rp);
	prune_cache_entries();
	goto setup_entry;
	}
	}

	/* Drop the lock and allocate a new entry */
	spin_unlock(&cache_lock);
	rp = nfsd_reply_cache_alloc();
	if (!rp) {
	dprintk("nfsd: unable to allocate DRC entry!\n");
	return RC_DOIT;
	}
	spin_lock(&cache_lock);
	++num_drc_entries;

	/*
	* Must search again just in case someone inserted one
	* after we dropped the lock above.
	*/
	found = nfsd_cache_search(rqstp, csum);
	if (found) {
	nfsd_reply_cache_free_locked(rp);
	rp = found;
	goto found_entry;
	}

	/*
	* We're keeping the one we just allocated. Are we now over the
	* limit? Prune one off the tip of the LRU in trade for the one we
	* just allocated if so.
	*/
	if (num_drc_entries >= max_drc_entries)
	nfsd_reply_cache_free_locked(list_first_entry(&lru_head,
	struct svc_cacherep, c_lru));

	setup_entry:
	nfsdstats.rcmisses++;
	rqstp->rq_cacherep = rp;
	rp->c_state = RC_INPROG;
	rp->c_xid = xid;
	rp->c_proc = proc;
	rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
	rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
	rp->c_prot = proto;
	rp->c_vers = vers;
	rp->c_len = rqstp->rq_arg.len;
	rp->c_csum = csum;

	hash_refile(rp);
	lru_put_end(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:
	nfsdstats.rchits++;
	/* We found a matching entry which is either in progress or done. */
	age = jiffies - rp->c_timestamp;
	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);
	nfsd_reply_cache_free_locked(rp);
	}

	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 = rqstp->rq_cacherep;
	struct kvec resv = &rqstp->rq_res.head[0], cachv;
	int len;

	if (!rp)
	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)) {
	nfsd_reply_cache_free(rp);
	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) {
	nfsd_reply_cache_free(rp);
	return;
	}
	cachv->iov_len = len << 2;
	memcpy(cachv->iov_base, statp, len << 2);
	break;
	case RC_NOCACHE:
	nfsd_reply_cache_free(rp);
	return;
	}
	spin_lock(&cache_lock);
	lru_put_end(rp);
	rp->c_secure = rqstp->rq_secure;
	rp->c_type = cachetype;
	rp->c_state = RC_DONE;
	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;
	}