dbm/sdbm/sdbm.c

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2000 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
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 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

/*
 * sdbm - ndbm work-alike hashed database library
 * based on Per-Aake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
 * author: oz@nexus.yorku.ca
 * ex-public domain, ported to APR for Apache 2
 * core routines
 */

#include "apr.h"
#include "apr_file_io.h"
#include "apr_strings.h"
#include "apr_errno.h"
#include "apr_sdbm.h"

#include "sdbm_tune.h"
#include "sdbm_pair.h"
#include "sdbm_private.h"

#include <string.h>     /* for memset() */
#include <stdlib.h>     /* for malloc() and free() */

/*
 * forward
 */
static int getdbit (SDBM *, long);
static apr_status_t setdbit(SDBM *, long);
static apr_status_t getpage(SDBM *db, long);
static sdbm_datum getnext(SDBM *db);
static apr_status_t makroom(SDBM *, long, int);

/*
 * useful macros
 */
#define SDBM_IOERR	0x2	       /* data base I/O error */

#define bad(x)		((x).dptr == NULL || (x).dsize <= 0)
#define exhash(item)	sdbm_hash((item).dptr, (item).dsize)
#define ioerr(db)	((db)->flags |= SDBM_IOERR)

/* ### Does anything need these externally? */
#define sdbm_dirfno(db)	((db)->dirf)
#define sdbm_pagfno(db)	((db)->pagf)

#define OFF_PAG(off)	(apr_off_t) (off) * PBLKSIZ
#define OFF_DIR(off)	(apr_off_t) (off) * DBLKSIZ

static long masks[] = {
	000000000000, 000000000001, 000000000003, 000000000007,
	000000000017, 000000000037, 000000000077, 000000000177,
	000000000377, 000000000777, 000000001777, 000000003777,
	000000007777, 000000017777, 000000037777, 000000077777,
	000000177777, 000000377777, 000000777777, 000001777777,
	000003777777, 000007777777, 000017777777, 000037777777,
	000077777777, 000177777777, 000377777777, 000777777777,
	001777777777, 003777777777, 007777777777, 017777777777
};

const sdbm_datum sdbm_nullitem = { NULL, 0 };

static apr_status_t database_cleanup(void *data)
{
    SDBM *db = data;

    (void) apr_close(db->dirf);
    (void) sdbm_unlock(db);
    (void) apr_close(db->pagf);
    free(db);

    return APR_SUCCESS;
}

apr_status_t
sdbm_open(SDBM **db, const char *file, apr_int32_t flags, apr_fileperms_t perms, apr_pool_t *p)
{
    char *dirname = apr_pstrcat(p, file, SDBM_DIRFEXT, NULL);
    char *pagname = apr_pstrcat(p, file, SDBM_PAGFEXT, NULL);
    
    return sdbm_prep(db, dirname, pagname, flags, perms, p);
}

apr_status_t
sdbm_prep(SDBM **pdb, const char *dirname, const char *pagname, 
	  apr_int32_t flags, apr_fileperms_t perms, apr_pool_t *p)
{
        SDBM *db;
        apr_finfo_t finfo;
	apr_status_t status;

        *pdb = NULL;

	db = malloc(sizeof(*db));
        memset(db, 0, sizeof(*db));

	db->pool = p;

        /*
         * adjust user flags so that WRONLY becomes RDWR, 
         * as required by this package. Also set our internal
         * flag for RDONLY if needed.
         */
	if (!(flags & APR_WRITE)) {
	    db->flags = SDBM_RDONLY;
	}

	flags |= APR_BINARY | APR_READ;

        /*
         * open the files in sequence, and stat the dirfile.
         * If we fail anywhere, undo everything, return NULL.
         */

	if ((status = apr_open(&db->pagf, pagname, flags, perms, p))
	    != APR_SUCCESS)
            goto error;

        if ((status = sdbm_lock(db)) != APR_SUCCESS)
            goto error;

        if ((status = apr_open(&db->dirf, dirname, flags, perms, p))
            != APR_SUCCESS)
            goto error;

        /*
         * need the dirfile size to establish max bit number.
         */
        if ((status = apr_getfileinfo(&finfo, db->dirf)) != APR_SUCCESS)
            goto error;

        /*
         * zero size: either a fresh database, or one with a single,
         * unsplit data page: dirpage is all zeros.
         */
        db->dirbno = (!finfo.size) ? 0 : -1;
        db->pagbno = -1;
        db->maxbno = finfo.size * BYTESIZ;

        /* (apr_pcalloc zeroed the buffers) */

        /* make sure that we close the database at some point */
        apr_register_cleanup(p, db, database_cleanup, apr_null_cleanup);

        /* Done! */
        *pdb = db;
        return APR_SUCCESS;

  error:
        if (db->dirf != NULL)
            (void) apr_close(db->dirf);
        if (db->pagf != NULL) {
            (void) sdbm_unlock(db);
            (void) apr_close(db->pagf);
        }
        free(db);
        return status;
}

void
sdbm_close(SDBM *db)
{
    (void) apr_run_cleanup(db->pool, db, database_cleanup);
}

sdbm_datum
sdbm_fetch(SDBM *db, sdbm_datum key)
{
	if (db == NULL || bad(key))
		return sdbm_nullitem;

	if (getpage(db, exhash(key)) == APR_SUCCESS)
		return getpair(db->pagbuf, key);

	ioerr(db);
	return sdbm_nullitem;
}

static apr_status_t write_page(SDBM *db, const char *buf, long pagno)
{
    apr_status_t status;
    apr_off_t off = OFF_PAG(pagno);
    
    if ((status = apr_seek(db->pagf, APR_SET, &off)) != APR_SUCCESS ||
	(status = apr_full_write(db->pagf, buf, PBLKSIZ, NULL)) != APR_SUCCESS) {
	ioerr(db);
	return status;
    }
    
    return APR_SUCCESS;
}

apr_status_t
sdbm_delete(SDBM *db, const sdbm_datum key)
{
	apr_status_t status;

	if (db == NULL || bad(key))
		return APR_EINVAL;
	if (sdbm_rdonly(db))
		return APR_EINVAL;

	if (getpage(db, exhash(key)) == APR_SUCCESS) {
		if (!delpair(db->pagbuf, key))
			return -1;
/*
 * update the page file
 */
		if ((status = write_page(db, db->pagbuf, db->pagbno)) != APR_SUCCESS)
		    return status;


		return APR_SUCCESS;
	}

	ioerr(db);
	return APR_EACCES;
}

apr_status_t sdbm_store(SDBM *db, sdbm_datum key, sdbm_datum val, int flags)
{
	int need;
	register long hash;
	apr_status_t status;

	if (db == NULL || bad(key))
		return APR_EINVAL;
	if (sdbm_rdonly(db))
		return APR_EINVAL;

	need = key.dsize + val.dsize;
/*
 * is the pair too big (or too small) for this database ??
 */
	if (need < 0 || need > PAIRMAX)
		return APR_EINVAL;

	if ((status = getpage(db, (hash = exhash(key)))) == APR_SUCCESS) {

/*
 * if we need to replace, delete the key/data pair
 * first. If it is not there, ignore.
 */
		if (flags == SDBM_REPLACE)
			(void) delpair(db->pagbuf, key);
#ifdef SEEDUPS
		else if (duppair(db->pagbuf, key))
			return APR_EEXIST;
#endif
/*
 * if we do not have enough room, we have to split.
 */
		if (!fitpair(db->pagbuf, need))
		    if ((status = makroom(db, hash, need)) != APR_SUCCESS)
			return status;
/*
 * we have enough room or split is successful. insert the key,
 * and update the page file.
 */
		(void) putpair(db->pagbuf, key, val);

		if ((status = write_page(db, db->pagbuf, db->pagbno)) != APR_SUCCESS)
		    return status;

	/*
	 * success
	 */
		return APR_SUCCESS;
	}
	
	ioerr(db);
	return status;
}

/*
 * makroom - make room by splitting the overfull page
 * this routine will attempt to make room for SPLTMAX times before
 * giving up.
 */
static apr_status_t
makroom(SDBM *db, long hash, int need)
{
	long newp;
	char twin[PBLKSIZ];
	char *pag = db->pagbuf;
	char *new = twin;
	register int smax = SPLTMAX;
	apr_status_t status;

	do {
/*
 * split the current page
 */
		(void) splpage(pag, new, db->hmask + 1);
/*
 * address of the new page
 */
		newp = (hash & db->hmask) | (db->hmask + 1);

/*
 * write delay, read avoidence/cache shuffle:
 * select the page for incoming pair: if key is to go to the new page,
 * write out the previous one, and copy the new one over, thus making
 * it the current page. If not, simply write the new page, and we are
 * still looking at the page of interest. current page is not updated
 * here, as sdbm_store will do so, after it inserts the incoming pair.
 */
		if (hash & (db->hmask + 1)) {
		    if ((status = write_page(db, db->pagbuf, db->pagbno)) != APR_SUCCESS)
			return status;
			    
		    db->pagbno = newp;
		    (void) memcpy(pag, new, PBLKSIZ);
		}
		else {
		    if ((status = write_page(db, new, newp)) != APR_SUCCESS)
			return status;
		}

		if ((status = setdbit(db, db->curbit)) != APR_SUCCESS)
		    return status;
/*
 * see if we have enough room now
 */
		if (fitpair(pag, need))
		    return APR_SUCCESS;
/*
 * try again... update curbit and hmask as getpage would have
 * done. because of our update of the current page, we do not
 * need to read in anything. BUT we have to write the current
 * [deferred] page out, as the window of failure is too great.
 */
		db->curbit = 2 * db->curbit +
			((hash & (db->hmask + 1)) ? 2 : 1);
		db->hmask |= db->hmask + 1;
		
		if ((status = write_page(db, db->pagbuf, db->pagbno))
		    != APR_SUCCESS)
		    return status;
		
	} while (--smax);
/*
 * if we are here, this is real bad news. After SPLTMAX splits,
 * we still cannot fit the key. say goodnight.
 */
#if 0
	(void) write(2, "sdbm: cannot insert after SPLTMAX attempts.\n", 44);
#endif
	/* ### ENOSPC not really appropriate but better than nothing */
	return APR_ENOSPC;

}

/* Reads 'len' bytes from file 'f' at offset 'off' into buf.
 * 'off' is given relative to the start of the file.
 * If EOF is returned while reading, this is taken as success.
 */
static apr_status_t read_from(apr_file_t *f, void *buf, 
			     apr_off_t off, apr_size_t len)
{
    apr_status_t status;

    if ((status = apr_seek(f, APR_SET, &off)) != APR_SUCCESS ||
	((status = apr_full_read(f, buf, len, NULL)) != APR_SUCCESS)) {
	/* if EOF is reached, pretend we read all zero's */
	if (status == APR_EOF) {
	    memset(buf, 0, len);
	    status = APR_SUCCESS;
	}
	return status;
    }

    return APR_SUCCESS;
}

/*
 * the following two routines will break if
 * deletions aren't taken into account. (ndbm bug)
 */
sdbm_datum
sdbm_firstkey(SDBM *db)
{
/*
 * start at page 0
 */
	if (read_from(db->pagf, db->pagbuf, OFF_PAG(0), PBLKSIZ) != APR_SUCCESS) {
	    ioerr(db);
	    return sdbm_nullitem;
	}

	db->pagbno = 0;
	db->blkptr = 0;
	db->keyptr = 0;

	return getnext(db);
}

sdbm_datum
sdbm_nextkey(SDBM *db)
{
	return getnext(db);
}

/*
 * all important binary tree traversal
 */
static apr_status_t
getpage(SDBM *db, long hash)
{
	register int hbit;
	register long dbit;
	register long pagb;
	apr_status_t status;

	dbit = 0;
	hbit = 0;
	while (dbit < db->maxbno && getdbit(db, dbit))
		dbit = 2 * dbit + ((hash & (1 << hbit++)) ? 2 : 1);

	debug(("dbit: %d...", dbit));

	db->curbit = dbit;
	db->hmask = masks[hbit];

	pagb = hash & db->hmask;
/*
 * see if the block we need is already in memory.
 * note: this lookaside cache has about 10% hit rate.
 */
	if (pagb != db->pagbno) { 
/*
 * note: here, we assume a "hole" is read as 0s.
 * if not, must zero pagbuf first.
 * ### joe: this assumption was surely never correct? but
 * ### we make it so in read_from anyway.
 */
		if ((status = read_from(db->pagf, db->pagbuf, OFF_PAG(pagb), PBLKSIZ)) 
		    != APR_SUCCESS) {
		    ioerr(db);		    
		    return status;
		}

		if (!chkpage(db->pagbuf))
		    return APR_ENOSPC; /* ### better error? */
		db->pagbno = pagb;

		debug(("pag read: %d\n", pagb));
	}
	return APR_SUCCESS;
}

static int
getdbit(SDBM *db, long dbit)
{
	register long c;
	register long dirb;

	c = dbit / BYTESIZ;
	dirb = c / DBLKSIZ;

	if (dirb != db->dirbno) {
		if (read_from(db->dirf, db->dirbuf, OFF_DIR(dirb), DBLKSIZ)
		    != APR_SUCCESS)
		    return 0;

		db->dirbno = dirb;

		debug(("dir read: %d\n", dirb));
	}

	return db->dirbuf[c % DBLKSIZ] & (1 << dbit % BYTESIZ);
}

static apr_status_t
setdbit(SDBM *db, long dbit)
{
	register long c;
	register long dirb;
	apr_status_t status;
	apr_off_t off;

	c = dbit / BYTESIZ;
	dirb = c / DBLKSIZ;

	if (dirb != db->dirbno) {
	    if ((status = read_from(db->dirf, db->dirbuf, OFF_DIR(dirb), DBLKSIZ))
		!= APR_SUCCESS)
		return status;

	    db->dirbno = dirb;
	    
	    debug(("dir read: %d\n", dirb));
	}

	db->dirbuf[c % DBLKSIZ] |= (1 << dbit % BYTESIZ);

	if (dbit >= db->maxbno)
		db->maxbno += DBLKSIZ * BYTESIZ;

	off = OFF_DIR(dirb);
	if (((status = apr_seek(db->dirf, APR_SET, &off)) != APR_SUCCESS)
	    || (status = apr_full_write(db->dirf, db->dirbuf, DBLKSIZ,
                                       NULL)) != APR_SUCCESS) {
	    return status;
        }

	return APR_SUCCESS;
}

/*
 * getnext - get the next key in the page, and if done with
 * the page, try the next page in sequence
 */
static sdbm_datum
getnext(SDBM *db)
{
	sdbm_datum key;

	for (;;) {
		db->keyptr++;
		key = getnkey(db->pagbuf, db->keyptr);
		if (key.dptr != NULL)
			return key;
/*
 * we either run out, or there is nothing on this page..
 * try the next one... If we lost our position on the
 * file, we will have to seek.
 */
		db->keyptr = 0;
		if (db->pagbno != db->blkptr++) {
		    apr_off_t off = OFF_PAG(db->blkptr);
		    if (apr_seek(db->pagf, APR_SET, &off) != APR_SUCCESS)
			break;
		}

		db->pagbno = db->blkptr;
		/* ### EOF acceptable here too? */
		if (apr_full_read(db->pagf, db->pagbuf, PBLKSIZ, NULL) != APR_SUCCESS)
			break;
		if (!chkpage(db->pagbuf))
			break;
	}
		
	ioerr(db);
	return sdbm_nullitem;
}


int sdbm_rdonly(SDBM *db)
{
    return ((db)->flags & SDBM_RDONLY);
}

int sdbm_error(SDBM *db)
{
    return ((db)->flags & SDBM_IOERR);
}

int sdbm_clearerr(SDBM *db)
{
    return ((db)->flags &= ~SDBM_IOERR);  /* ouch */
}