Started development on the SNMP polling daemon.

1 files changed, 367 insertions, 0 deletions

diff --git a/src/common/hash.c b/src/common/hash.c
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+/*
+ * Copyright (c) 2004, Nate Nielsen
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *     * Redistributions of source code must retain the above
+ *       copyright notice, this list of conditions and the
+ *       following disclaimer.
+ *     * Redistributions in binary form must reproduce the
+ *       above copyright notice, this list of conditions and
+ *       the following disclaimer in the documentation and/or
+ *       other materials provided with the distribution.
+ *     * The names of contributors to this software may not be
+ *       used to endorse or promote products derived from this
+ *       software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+ * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+/*
+ * Originally from apache 2.0
+ * Modifications for general use by <nielsen@memberwebs.com>
+ */
+
+/* Copyright 2000-2004 The Apache Software Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <sys/types.h>
+#include <stdlib.h>
+#include "hash.h"
+
+#define KEY_DATA(he) (void*)(((unsigned char*)(he)) + sizeof(*(he)))
+
+/*
+ * The internal form of a hash table.
+ *
+ * The table is an array indexed by the hash of the key; collisions
+ * are resolved by hanging a linked list of hash entries off each
+ * element of the array. Although this is a really simple design it
+ * isn't too bad given that pools have a low allocation overhead.
+ */
+
+typedef struct hsh_entry_t hsh_entry_t;
+
+struct hsh_entry_t
+{
+    hsh_entry_t* next;
+    unsigned int hash;
+    const void* val;
+};
+
+/*
+ * Data structure for iterating through a hash table.
+ *
+ * We keep a pointer to the next hash entry here to allow the current
+ * hash entry to be freed or otherwise mangled between calls to
+ * hsh_next().
+ */
+struct hsh_index_t
+{
+    hsh_t* ht;
+    hsh_entry_t* ths;
+    hsh_entry_t* next;
+    unsigned int index;
+};
+
+/*
+ * The size of the array is always a power of two. We use the maximum
+ * index rather than the size so that we can use bitwise-AND for
+ * modular arithmetic.
+ * The count of hash entries may be greater depending on the chosen
+ * collision rate.
+ */
+struct hsh_t
+{
+    hsh_entry_t** array;
+    hsh_index_t iterator;    /* For hsh_first(...) */
+    unsigned int count;
+    unsigned int max;
+    unsigned int klen;
+};
+
+
+#define INITIAL_MAX 15 /* tunable == 2^n - 1 */
+#define int_malloc malloc
+#define int_free free
+
+
+/*
+ * Hash creation functions.
+ */
+
+static hsh_entry_t** alloc_array(hsh_t* ht, unsigned int max)
+{
+    return int_calloc(sizeof(*(ht->array)) * (max + 1));
+}
+
+hsh_t* hsh_create(size_t klen)
+{
+    hsh_t* ht = int_malloc(sizeof(hsh_t));
+    if(ht)
+    {
+        ht->count = 0;
+        ht->max = INITIAL_MAX;
+        ht->array = alloc_array(ht, ht->max);
+        ht->klen = klen;
+        if(!ht->array)
+        {
+            int_free(ht);
+            return NULL;
+        }
+    }
+    return ht;
+}
+
+void hsh_free(hsh_t* ht)
+{
+    hsh_index_t* hi;
+
+    for(hi = hsh_first(ht); hi; hi = hsh_next(hi))
+        int_free(hi->ths);
+
+    if(ht->array)
+        int_free(ht->array);
+
+    int_free(ht);
+}
+
+/*
+ * Hash iteration functions.
+ */
+
+hsh_index_t* hsh_next(hsh_index_t* hi)
+{
+    hi->ths = hi->next;
+    while(!hi->ths)
+    {
+        if(hi->index > hi->ht->max)
+            return NULL;
+
+        hi->ths = hi->ht->array[hi->index++];
+    }
+    hi->next = hi->ths->next;
+    return hi;
+}
+
+hsh_index_t* hsh_first(hsh_t* ht)
+{
+    hsh_index_t* hi = &ht->iterator;
+
+    hi->ht = ht;
+    hi->index = 0;
+    hi->ths = NULL;
+    hi->next = NULL;
+    return hsh_next(hi);
+}
+
+void* hsh_this(hsh_index_t* hi, const void** key)
+{
+    if(key)
+        *key = KEY_DATA(hi->ths);
+    return (void*)hi->ths->val;
+}
+
+
+/*
+ * Expanding a hash table
+ */
+
+static int expand_array(hsh_t* ht)
+{
+    hsh_index_t* hi;
+    hsh_entry_t** new_array;
+    unsigned int new_max;
+
+    new_max = ht->max * 2 + 1;
+    new_array = alloc_array(ht, new_max);
+
+    if(!new_array)
+        return 0;
+
+    for(hi = hsh_first(ht); hi; hi = hsh_next(hi))
+    {
+        unsigned int i = hi->ths->hash & new_max;
+        hi->ths->next = new_array[i];
+        new_array[i] = hi->ths;
+    }
+
+    if(ht->array)
+        free(ht->array);
+
+    ht->array = new_array;
+    ht->max = new_max;
+    return 1;
+}
+
+/*
+ * This is where we keep the details of the hash function and control
+ * the maximum collision rate.
+ *
+ * If val is non-NULL it creates and initializes a new hash entry if
+ * there isn't already one there; it returns an updatable pointer so
+ * that hash entries can be removed.
+ */
+
+static hsh_entry_t** find_entry(hsh_t* ht, const void* key, const void* val)
+{
+    hsh_entry_t** hep;
+    hsh_entry_t* he;
+    const unsigned char* p;
+    unsigned int hash;
+    size_t i;
+
+    size_t klen = ht->klen;
+
+    /*
+     * This is the popular `times 33' hash algorithm which is used by
+     * perl and also appears in Berkeley DB. This is one of the best
+     * known hash functions for strings because it is both computed
+     * very fast and distributes very well.
+     *
+     * The originator may be Dan Bernstein but the code in Berkeley DB
+     * cites Chris Torek as the source. The best citation I have found
+     * is "Chris Torek, Hash function for text in C, Usenet message
+     * <27038@mimsy.umd.edu> in comp.lang.c , October, 1990." in Rich
+     * Salz's USENIX 1992 paper about INN which can be found at
+     * <http://citeseer.nj.nec.com/salz92internetnews.html>.
+     *
+     * The magic of number 33, i.e. why it works better than many other
+     * constants, prime or not, has never been adequately explained by
+     * anyone. So I try an explanation: if one experimentally tests all
+     * multipliers between 1 and 256 (as I did while writing a low-level
+     * data structure library some time ago) one detects that even
+     * numbers are not useable at all. The remaining 128 odd numbers
+     * (except for the number 1) work more or less all equally well.
+     * They all distribute in an acceptable way and this way fill a hash
+     * table with an average percent of approx. 86%.
+     *
+     * If one compares the chi^2 values of the variants (see
+     * Bob Jenkins ``Hashing Frequently Asked Questions'' at
+     * http://burtleburtle.net/bob/hash/hashfaq.html for a description
+     * of chi^2), the number 33 not even has the best value. But the
+     * number 33 and a few other equally good numbers like 17, 31, 63,
+     * 127 and 129 have nevertheless a great advantage to the remaining
+     * numbers in the large set of possible multipliers: their multiply
+     * operation can be replaced by a faster operation based on just one
+     * shift plus either a single addition or subtraction operation. And
+     * because a hash function has to both distribute good _and_ has to
+     * be very fast to compute, those few numbers should be preferred.
+     *
+     *                        -- Ralf S. Engelschall <rse@engelschall.com>
+     */
+    hash = 0;
+
+    {
+        for(p = key, i = klen; i; i--, p++)
+            hash = hash * 33 + *p;
+    }
+
+    /* scan linked list */
+    for(hep = &ht->array[hash & ht->max], he = *hep;
+            he; hep = &he->next, he = *hep)
+    {
+     if(he->hash == hash &&
+        memcmp(KEY_DATA(he), key, klen) == 0)
+         break;
+    }
+
+    if(he || !val)
+        return hep;
+
+    /* add a new entry for non-NULL val */
+    he = int_malloc(sizeof(*he) + klen);
+    if(he)
+    {
+        /* Key data points past end of entry */
+        memcpy(KEY_DATA(he), key, klen);
+
+        he->next = NULL;
+        he->hash = hash;
+        he->val = val;
+
+        *hep = he;
+        ht->count++;
+    }
+
+    return hep;
+}
+
+void* hsh_get(hsh_t* ht, const void *key)
+{
+        hsh_entry_t** he = find_entry(ht, key, NULL);
+        if(he && *he)
+            return (void*)((*he)->val);
+        else
+            return NULL;
+}
+
+int hsh_set(hsh_t* ht, const void* key, void* val)
+{
+    hsh_entry_t** hep = find_entry(ht, key, val);
+
+    if(hep && *hep)
+    {
+        /* replace entry */
+        (*hep)->val = val;
+
+        /* check that the collision rate isn't too high */
+        if(ht->count > ht->max)
+        {
+            if(!expand_array(ht))
+                return 0;
+        }
+
+        return 1;
+    }
+
+    return 0;
+}
+
+void* hsh_rem(hsh_t* ht, const void* key)
+{
+    hsh_entry_t** hep = find_entry(ht, key, NULL);
+    void* val = NULL;
+
+    if(hep && *hep)
+    {
+        hsh_entry_t* old = *hep;
+        *hep = (*hep)->next;
+        --ht->count;
+        val = (void*)old->val;
+        free(old);
+    }
+
+    return val;
+}
+
+unsigned int hsh_count(hsh_t* ht)
+{
+    return ht->count;
+}