1 /*- 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Margo Seltzer. 7 * 8 * %sccs.include.redist.c% 9 * 10 * @(#)page.h 8.1 (Berkeley) 06/06/93 11 */ 12 13 /* 14 * Definitions for hashing page file format. 15 */ 16 17 /* 18 * routines dealing with a data page 19 * 20 * page format: 21 * +------------------------------+ 22 * p | n | keyoff | datoff | keyoff | 23 * +------------+--------+--------+ 24 * | datoff | free | ptr | --> | 25 * +--------+---------------------+ 26 * | F R E E A R E A | 27 * +--------------+---------------+ 28 * | <---- - - - | data | 29 * +--------+-----+----+----------+ 30 * | key | data | key | 31 * +--------+----------+----------+ 32 * 33 * Pointer to the free space is always: p[p[0] + 2] 34 * Amount of free space on the page is: p[p[0] + 1] 35 */ 36 37 /* 38 * How many bytes required for this pair? 39 * 2 shorts in the table at the top of the page + room for the 40 * key and room for the data 41 * 42 * We prohibit entering a pair on a page unless there is also room to append 43 * an overflow page. The reason for this it that you can get in a situation 44 * where a single key/data pair fits on a page, but you can't append an 45 * overflow page and later you'd have to split the key/data and handle like 46 * a big pair. 47 * You might as well do this up front. 48 */ 49 50 #define PAIRSIZE(K,D) (2*sizeof(u_short) + (K)->size + (D)->size) 51 #define BIGOVERHEAD (4*sizeof(u_short)) 52 #define KEYSIZE(K) (4*sizeof(u_short) + (K)->size); 53 #define OVFLSIZE (2*sizeof(u_short)) 54 #define FREESPACE(P) ((P)[(P)[0]+1]) 55 #define OFFSET(P) ((P)[(P)[0]+2]) 56 #define PAIRFITS(P,K,D) \ 57 (((P)[2] >= REAL_KEY) && \ 58 (PAIRSIZE((K),(D)) + OVFLSIZE) <= FREESPACE((P))) 59 #define PAGE_META(N) (((N)+3) * sizeof(u_short)) 60 61 typedef struct { 62 BUFHEAD *newp; 63 BUFHEAD *oldp; 64 BUFHEAD *nextp; 65 u_short next_addr; 66 } SPLIT_RETURN; 67