tdb.c

经典的ppp程序

/* 
 * Database functions
 * Copyright (C) Andrew Tridgell 1999
 * 
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms AND provided that this software or
 * any derived work is only used as part of the PPP daemon (pppd)
 * and related utilities.
 * The name of the author may not be used to endorse or promote products
 * derived from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Note: this software is also available under the Gnu Public License
 * version 2 or later.
 */

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include "tdb.h"

#define TDB_VERSION (0x26011967 + 1)
#define TDB_MAGIC (0x26011999U)
#define TDB_FREE_MAGIC (~TDB_MAGIC)
#define TDB_ALIGN 4
#define MIN_REC_SIZE (2*sizeof(struct list_struct) + TDB_ALIGN)
#define DEFAULT_HASH_SIZE 128
#define TDB_PAGE_SIZE 0x2000
#define TDB_LEN_MULTIPLIER 10
#define FREELIST_TOP (sizeof(struct tdb_header))

#define LOCK_SET 1
#define LOCK_CLEAR 0

/* lock offsets */
#define GLOBAL_LOCK 0
#define ACTIVE_LOCK 4
#define LIST_LOCK_BASE 1024

#define BUCKET(hash) ((hash) % tdb->header.hash_size)

#ifndef MAP_FILE
#define MAP_FILE 0
#endif

/* the body of the database is made of one list_struct for the free space
   plus a separate data list for each hash value */
struct list_struct {
	tdb_len rec_len; /* total byte length of record */
	tdb_off next; /* offset of the next record in the list */
	tdb_len key_len; /* byte length of key */
	tdb_len data_len; /* byte length of data */
	unsigned full_hash; /* the full 32 bit hash of the key */
	unsigned magic;   /* try to catch errors */
	/*
	   the following union is implied 
	   union {
              char record[rec_len];
	      struct {
	        char key[key_len];
		char data[data_len];
	      }
           }
	*/
};

/* a null data record - useful for error returns */
static TDB_DATA null_data;

/* a byte range locking function - return 0 on success
   this functions locks/unlocks 1 byte at the specified offset */
static int tdb_brlock(TDB_CONTEXT *tdb, tdb_off offset, 
		      int set, int rw_type, int lck_type)
{
#if NOLOCK
	return 0;
#else
	struct flock fl;

        if (tdb->fd == -1) return 0;   /* for in memory tdb */

	if (tdb->read_only) return -1;

	fl.l_type = set==LOCK_SET?rw_type:F_UNLCK;
	fl.l_whence = SEEK_SET;
	fl.l_start = offset;
	fl.l_len = 1;
	fl.l_pid = 0;

	if (fcntl(tdb->fd, lck_type, &fl) != 0) {
#if TDB_DEBUG
		if (lck_type == F_SETLKW) {
			printf("lock %d failed at %d (%s)\n", 
			       set, offset, strerror(errno));
		}
#endif
		tdb->ecode = TDB_ERR_LOCK;
		return -1;
	}
	return 0;
#endif
}

/* lock a list in the database. list -1 is the alloc list */
static int tdb_lock(TDB_CONTEXT *tdb, int list)
{
	if (list < -1 || list >= (int)tdb->header.hash_size) {
#if TDB_DEBUG
		printf("bad list %d\n", list);
#endif
		return -1;
	}
	if (tdb->locked[list+1] == 0) {
		if (tdb_brlock(tdb, LIST_LOCK_BASE + 4*list, LOCK_SET, 
			       F_WRLCK, F_SETLKW) != 0) {
			return -1;
		}
	}
	tdb->locked[list+1]++;
	return 0;
}

/* unlock the database. */
static int tdb_unlock(TDB_CONTEXT *tdb, int list)
{
	if (list < -1 || list >= (int)tdb->header.hash_size) {
#if TDB_DEBUG
		printf("bad unlock list %d\n", list);
#endif
		return -1;
	}

	if (tdb->locked[list+1] == 0) {
#if TDB_DEBUG
		printf("not locked %d\n", list);
#endif
		tdb->ecode = TDB_ERR_LOCK;
		return -1;
	}
	if (tdb->locked[list+1] == 1) {
		if (tdb_brlock(tdb, LIST_LOCK_BASE + 4*list, LOCK_CLEAR, 
			       F_WRLCK, F_SETLKW) != 0) {
			return -1;
		}
	}
	tdb->locked[list+1]--;
	return 0;
}

/* the hash algorithm - turn a key into an integer
   This is based on the hash agorithm from gdbm */
static unsigned tdb_hash(TDB_DATA *key)
{
	unsigned value;	/* Used to compute the hash value.  */
	unsigned   i;	/* Used to cycle through random values. */

	/* Set the initial value from the key size. */
	value = 0x238F13AF * key->dsize;
	for (i=0; i < key->dsize; i++) {
		value = (value + (key->dptr[i] << (i*5 % 24)));
	}

	value = (1103515243 * value + 12345);  

	return value;
}

/* find the top of the hash chain for an open database */
static tdb_off tdb_hash_top(TDB_CONTEXT *tdb, unsigned hash)
{
	tdb_off ret;
	hash = BUCKET(hash);
	ret = FREELIST_TOP + (hash+1)*sizeof(tdb_off);
	return ret;
}


/* check for an out of bounds access - if it is out of bounds then
   see if the database has been expanded by someone else and expand
   if necessary */
static int tdb_oob(TDB_CONTEXT *tdb, tdb_off offset)
{
	struct stat st;
	if ((offset <= tdb->map_size) || (tdb->fd == -1)) return 0;

	fstat(tdb->fd, &st);
	if (st.st_size <= (ssize_t)offset) {
		tdb->ecode = TDB_ERR_IO;
		return -1;
	}

#if HAVE_MMAP
	if (tdb->map_ptr) {
		munmap(tdb->map_ptr, tdb->map_size);
		tdb->map_ptr = NULL;
	}
#endif

	tdb->map_size = st.st_size;
#if HAVE_MMAP
	tdb->map_ptr = (void *)mmap(NULL, tdb->map_size, 
				    tdb->read_only?PROT_READ:PROT_READ|PROT_WRITE,
				    MAP_SHARED | MAP_FILE, tdb->fd, 0);
#endif	
	return 0;
}


/* write a lump of data at a specified offset */
static int tdb_write(TDB_CONTEXT *tdb, tdb_off offset, const char *buf, tdb_len len)
{
	if (tdb_oob(tdb, offset + len) != 0) {
		/* oops - trying to write beyond the end of the database! */
		return -1;
	}

	if (tdb->map_ptr) {
		memcpy(offset + (char *)tdb->map_ptr, buf, len);
	} else {
		if (lseek(tdb->fd, offset, SEEK_SET) != offset ||
		    write(tdb->fd, buf, len) != (ssize_t)len) {
			tdb->ecode = TDB_ERR_IO;
			return -1;
		}
	}
	return 0;
}

/* read a lump of data at a specified offset */
static int tdb_read(TDB_CONTEXT *tdb, tdb_off offset, char *buf, tdb_len len)
{
	if (tdb_oob(tdb, offset + len) != 0) {
		/* oops - trying to read beyond the end of the database! */
		return -1;
	}

	if (tdb->map_ptr) {
		memcpy(buf, offset + (char *)tdb->map_ptr, len);
	} else {
		if (lseek(tdb->fd, offset, SEEK_SET) != offset ||
		    read(tdb->fd, buf, len) != (ssize_t)len) {
			tdb->ecode = TDB_ERR_IO;
			return -1;
		}
	}
	return 0;
}


/* read a lump of data, allocating the space for it */
static char *tdb_alloc_read(TDB_CONTEXT *tdb, tdb_off offset, tdb_len len)
{
	char *buf;

	buf = (char *)malloc(len);

	if (!buf) {
		tdb->ecode = TDB_ERR_OOM;
		return NULL;
	}

	if (tdb_read(tdb, offset, buf, len) == -1) {
		free(buf);
		return NULL;
	}
	
	return buf;
}

/* convenience routine for writing a record */
static int rec_write(TDB_CONTEXT *tdb, tdb_off offset, struct list_struct *rec)
{
	return tdb_write(tdb, offset, (char *)rec, sizeof(*rec));
}

/* convenience routine for writing a tdb_off */
static int ofs_write(TDB_CONTEXT *tdb, tdb_off offset, tdb_off *d)
{
	return tdb_write(tdb, offset, (char *)d, sizeof(*d));
}

/* read a tdb_off from the store */
static int ofs_read(TDB_CONTEXT *tdb, tdb_off offset, tdb_off *d)
{
	return tdb_read(tdb, offset, (char *)d, sizeof(*d));
}

/* read a record and check for simple errors */
static int rec_read(TDB_CONTEXT *tdb, tdb_off offset, struct list_struct *rec)
{
	if (tdb_read(tdb, offset, (char *)rec, sizeof(*rec)) == -1) return -1;
	if (rec->magic != TDB_MAGIC) {
#if TDB_DEBUG
		printf("bad magic 0x%08x at offset %d\n",
		       rec->magic, offset);
#endif
		tdb->ecode = TDB_ERR_CORRUPT;
		return -1;
	}
	if (tdb_oob(tdb, rec->next) != 0) {
		return -1;
	}
	return 0;
}

/* expand the database at least length bytes by expanding the
   underlying file and doing the mmap again if necessary */
static int tdb_expand(TDB_CONTEXT *tdb, tdb_off length)
{
	struct list_struct rec;
	tdb_off offset, ptr;
	char b = 0;

	tdb_lock(tdb,-1);

	/* make sure we know about any previous expansions by another
           process */
	tdb_oob(tdb,tdb->map_size + 1);

	/* always make room for at least 10 more records */
	length *= TDB_LEN_MULTIPLIER;

	/* and round the database up to a multiple of TDB_PAGE_SIZE */
	length = ((tdb->map_size + length + TDB_PAGE_SIZE) & ~(TDB_PAGE_SIZE - 1)) - tdb->map_size;

	/* expand the file itself */
        if (tdb->fd != -1) {
            lseek(tdb->fd, tdb->map_size + length - 1, SEEK_SET);
            if (write(tdb->fd, &b, 1) != 1) goto fail;
        }

	/* form a new freelist record */
	offset = FREELIST_TOP;
	rec.rec_len = length - sizeof(rec);
	rec.magic = TDB_FREE_MAGIC;
	if (ofs_read(tdb, offset, &rec.next) == -1) {
		goto fail;
	}

#if HAVE_MMAP
	if (tdb->fd != -1 && tdb->map_ptr) {
		munmap(tdb->map_ptr, tdb->map_size);
		tdb->map_ptr = NULL;
	}
#endif

	tdb->map_size += length;

        if (tdb->fd == -1) {
            tdb->map_ptr = realloc(tdb->map_ptr, tdb->map_size);
        }

	/* write it out */
	if (rec_write(tdb, tdb->map_size - length, &rec) == -1) {
		goto fail;
	}

	/* link it into the free list */
	ptr = tdb->map_size - length;
	if (ofs_write(tdb, offset, &ptr) == -1) goto fail;

#if HAVE_MMAP
        if (tdb->fd != -1) {
            tdb->map_ptr = (void *)mmap(NULL, tdb->map_size, 
                                        PROT_READ|PROT_WRITE,
                                        MAP_SHARED | MAP_FILE, tdb->fd, 0);
        }
#endif

	tdb_unlock(tdb, -1);
	return 0;

 fail:
	tdb_unlock(tdb,-1);
	return -1;
}

/* allocate some space from the free list. The offset returned points
   to a unconnected list_struct within the database with room for at
   least length bytes of total data

   0 is returned if the space could not be allocated
 */
static tdb_off tdb_allocate(TDB_CONTEXT *tdb, tdb_len length)
{
	tdb_off offset, rec_ptr, last_ptr;
	struct list_struct rec, lastrec, newrec;

	tdb_lock(tdb, -1);

 again:
	last_ptr = 0;
	offset = FREELIST_TOP;

	/* read in the freelist top */
	if (ofs_read(tdb, offset, &rec_ptr) == -1) {
		goto fail;
	}

	/* keep looking until we find a freelist record that is big
           enough */
	while (rec_ptr) {
		if (tdb_read(tdb, rec_ptr, (char *)&rec, sizeof(rec)) == -1) {
			goto fail;
		}

		if (rec.magic != TDB_FREE_MAGIC) {
#if TDB_DEBUG
			printf("bad magic 0x%08x in free list\n", rec.magic);
#endif
			goto fail;
		}

		if (rec.rec_len >= length) {
			/* found it - now possibly split it up  */
			if (rec.rec_len > length + MIN_REC_SIZE) {
				length = (length + TDB_ALIGN) & ~(TDB_ALIGN-1);

				newrec.rec_len = rec.rec_len - (sizeof(rec) + length);
				newrec.next = rec.next;
				newrec.magic = TDB_FREE_MAGIC;

				rec.rec_len = length;
				rec.next = rec_ptr + sizeof(rec) + rec.rec_len;
				
				if (rec_write(tdb, rec.next, &newrec) == -1) {
					goto fail;
				}

				if (rec_write(tdb, rec_ptr, &rec) == -1) {
					goto fail;
				}
			}

			/* remove it from the list */
			if (last_ptr == 0) {
				offset = FREELIST_TOP;

				if (ofs_write(tdb, offset, &rec.next) == -1) {
					goto fail;
				}				
			} else {
				lastrec.next = rec.next;
				if (rec_write(tdb, last_ptr, &lastrec) == -1) {
					goto fail;
				}
			}

			/* all done - return the new record offset */
			tdb_unlock(tdb, -1);
			return rec_ptr;
		}

		/* move to the next record */
		lastrec = rec;
		last_ptr = rec_ptr;
		rec_ptr = rec.next;
	}

	/* we didn't find enough space. See if we can expand the
	   database and if we can then try again */
	if (tdb_expand(tdb, length + sizeof(rec)) == 0) goto again;

 fail:
#if TDB_DEBUG
	printf("tdb_allocate failed for size %u\n", length);
#endif
	tdb_unlock(tdb, -1);
	return 0;
}

/* initialise a new database with a specified hash size */
static int tdb_new_database(TDB_CONTEXT *tdb, int hash_size)
{
	struct tdb_header header;
	tdb_off offset;
	int i, size = 0;
	tdb_off buf[16];

        /* create the header */
        memset(&header, 0, sizeof(header));
        memcpy(header.magic_food, TDB_MAGIC_FOOD, strlen(TDB_MAGIC_FOOD)+1);
        header.version = TDB_VERSION;
        header.hash_size = hash_size;
        lseek(tdb->fd, 0, SEEK_SET);
        ftruncate(tdb->fd, 0);
        
        if (tdb->fd != -1 && write(tdb->fd, &header, sizeof(header)) != 
            sizeof(header)) {
            tdb->ecode = TDB_ERR_IO;
            return -1;
        } else size += sizeof(header);
	
        /* the freelist and hash pointers */
        offset = 0;
        memset(buf, 0, sizeof(buf));

        for (i=0;(hash_size+1)-i >= 16; i += 16) {
            if (tdb->fd != -1 && write(tdb->fd, buf, sizeof(buf)) != 
                sizeof(buf)) {
                tdb->ecode = TDB_ERR_IO;
                return -1;
            } else size += sizeof(buf);
        }

        for (;i<hash_size+1; i++) {
            if (tdb->fd != -1 && write(tdb->fd, buf, sizeof(tdb_off)) != 
                sizeof(tdb_off)) {
                tdb->ecode = TDB_ERR_IO;
                return -1;
            } else size += sizeof(tdb_off);
        }

        if (tdb->fd == -1) {
            tdb->map_ptr = calloc(size, 1);
            tdb->map_size = size;
            if (tdb->map_ptr == NULL) {
                tdb->ecode = TDB_ERR_IO;
                return -1;
            }
            memcpy(&tdb->header, &header, sizeof(header));
        }

#if TDB_DEBUG
	printf("initialised database of hash_size %u\n", 
	       hash_size);
#endif
	return 0;
}

/* Returns 0 on fail.  On success, return offset of record, and fills
   in rec */
static tdb_off tdb_find(TDB_CONTEXT *tdb, TDB_DATA key, unsigned int hash,
			struct list_struct *rec)
{
	tdb_off offset, rec_ptr;
	
	/* find the top of the hash chain */
	offset = tdb_hash_top(tdb, hash);

	/* read in the hash top */
	if (ofs_read(tdb, offset, &rec_ptr) == -1)
		return 0;

	/* keep looking until we find the right record */
	while (rec_ptr) {
		if (rec_read(tdb, rec_ptr, rec) == -1)
			return 0;

		if (hash == rec->full_hash && key.dsize == rec->key_len) {
			char *k;
			/* a very likely hit - read the key */
			k = tdb_alloc_read(tdb, rec_ptr + sizeof(*rec), 
					   rec->key_len);

			if (!k)
				return 0;

			if (memcmp(key.dptr, k, key.dsize) == 0) {
				free(k);
				return rec_ptr;
			}
			free(k);
		}

		/* move to the next record */
		rec_ptr = rec->next;
	}
	return 0;
}

/* 
   return an error string for the last tdb error
*/
char *tdb_error(TDB_CONTEXT *tdb)
{
	int i;
	static struct {
		enum TDB_ERROR ecode;
		char *estring;
	} emap[] = {
		{TDB_SUCCESS, "Success"},
		{TDB_ERR_CORRUPT, "Corrupt database"},
		{TDB_ERR_IO, "IO Error"},
		{TDB_ERR_LOCK, "Locking error"},
		{TDB_ERR_OOM, "Out of memory"},
		{TDB_ERR_EXISTS, "Record exists"},
		{-1, NULL}};
        if (tdb != NULL) {
            for (i=0;emap[i].estring;i++) {
		if (tdb->ecode == emap[i].ecode) return emap[i].estring;
            }
        } else {
            return "Invalid tdb context";
        }
	return "Invalid error code";
}


/* update an entry in place - this only works if the new data size
   is <= the old data size and the key exists.
   on failure return -1
*/
int tdb_update(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf)
{
	unsigned hash;
	struct list_struct rec;
	tdb_off rec_ptr;
	int ret = -1;

        if (tdb == NULL) {
#ifdef TDB_DEBUG
            printf("tdb_update() called with null context\n");
#endif
            return -1;
        }

	/* find which hash bucket it is in */
	hash = tdb_hash(&key);

	tdb_lock(tdb, BUCKET(hash));
	rec_ptr = tdb_find(tdb, key, hash, &rec);

	if (!rec_ptr)
		goto out;

	/* must be long enough */
	if (rec.rec_len < key.dsize + dbuf.dsize)
		goto out;

	if (tdb_write(tdb, rec_ptr + sizeof(rec) + rec.key_len,
		      dbuf.dptr, dbuf.dsize) == -1)
		goto out;