nfscache.c

Go to the documentation of this file.

/*
 * 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 <[email protected]>
 */

#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)
{
    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 type = rqstp->rq_cachetype;
    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;
}