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1.1 root 1: /*
2: * The header for buffers in the buffer pool and otherwise used
3: * to describe a block i/o request is given here. The routines
4: * which manipulate these things are given in bio.c.
5: *
6: * Each buffer in the pool is usually doubly linked into 2 lists:
7: * hashed into a chain by <dev,blkno> so it can be located in the cache,
8: * and (usually) on (one of several) queues. These lists are circular and
9: * doubly linked for easy removal.
10: *
11: * There are currently three queues for buffers:
12: * one for buffers which must be kept permanently (super blocks)
13: * one for buffers containing ``useful'' information (the cache)
14: * one for buffers containing ``non-useful'' information
15: * (and empty buffers, pushed onto the front)
16: * The latter two queues contain the buffers which are available for
17: * reallocation, are kept in lru order. When not on one of these queues,
18: * the buffers are ``checked out'' to drivers which use the available list
19: * pointers to keep track of them in their i/o active queues.
20: */
21:
22: /*
23: * Bufhd structures used at the head of the hashed buffer queues.
24: * We only need three words for these, so this abbreviated
25: * definition saves some space.
26: */
27: struct bufhd
28: {
29: long b_flags; /* see defines below */
30: struct buf *b_forw, *b_back; /* fwd/bkwd pointer in chain */
31: };
32: struct buf
33: {
34: long b_flags; /* too much goes here to describe */
35: struct buf *b_forw, *b_back; /* hash chain (2 way street) */
36: struct buf *av_forw, *av_back; /* position on free list if not BUSY */
37: #define b_actf av_forw /* alternate names for driver queue */
38: #define b_actl av_back /* head - isn't history wonderful */
39: long b_bcount; /* transfer count */
40: #define b_active b_bcount /* driver queue head: drive active */
41: short b_error; /* returned after I/O */
42: dev_t b_dev; /* major+minor device name */
43: union {
44: caddr_t b_addr; /* low order core address */
45: int *b_words; /* words for clearing */
46: struct filsys *b_filsys; /* superblocks */
47: struct dinode *b_dino; /* ilist */
48: daddr_t *b_daddr; /* indirect block */
49: } b_un;
50: daddr_t b_blkno; /* block # on device */
51: long b_resid; /* words not transferred after error */
52: #define b_errcnt b_resid /* while i/o in progress: # retries */
53: #define b_pfcent b_resid /* garbage: don't ask */
54: struct proc *b_proc; /* proc doing physical or swap I/O */
55: };
56:
57: #define BQUEUES 3 /* number of free buffer queues */
58: #define BQ_LOCKED 0 /* super-blocks &c */
59: #define BQ_LRU 1 /* lru, useful buffers */
60: #define BQ_AGE 2 /* rubbish */
61:
62: #ifdef KERNEL
63: struct buf *buf; /* the buffer pool itself */
64: char *buffers;
65: int nbuf;
66: struct buf *swbuf; /* swap I/O headers */
67: int nswbuf;
68: short *swsize;
69: int *swpf;
70: struct buf bfreelist[BQUEUES]; /* heads of available lists */
71: struct buf bswlist; /* head of free swap header list */
72: struct buf *bclnlist; /* head of cleaned page list */
73:
74: struct buf *alloc();
75: struct buf *baddr();
76: struct buf *getblk();
77: struct buf *geteblk();
78: struct buf *bread();
79: struct buf *breada();
80:
81: unsigned minphys();
82: #endif
83:
84: /*
85: * These flags are kept in b_flags.
86: */
87: #define B_WRITE 0x000000 /* non-read pseudo-flag */
88: #define B_READ 0x000001 /* read when I/O occurs */
89: #define B_DONE 0x000002 /* transaction finished */
90: #define B_ERROR 0x000004 /* transaction aborted */
91: #define B_BUSY 0x000008 /* not on av_forw/back list */
92: #define B_PHYS 0x000010 /* physical IO */
93: #define B_HDR 0x000020 /* was B_MAP, now ioctl */
94: #define B_WANTED 0x000040 /* issue wakeup when BUSY goes off */
95: #define B_AGE 0x000080 /* delayed write for correct aging */
96: #define B_ASYNC 0x000100 /* don't wait for I/O completion */
97: #define B_DELWRI 0x000200 /* write at exit of avail list */
98: #define B_TAPE 0x000400 /* this is a magtape (no bdwrite) */
99: #define B_UAREA 0x000800 /* add u-area to a swap operation */
100: #define B_PAGET 0x001000 /* page in/out of page table space */
101: #define B_DIRTY 0x002000 /* dirty page to be pushed out async */
102: #define B_PGIN 0x004000 /* pagein op, so swap() can count it */
103: #define B_CACHE 0x008000 /* did bread find us in the cache ? */
104: #define B_INVAL 0x010000 /* does not contain valid info */
105: #define B_LOCKED 0x020000 /* locked in core (not reusable) */
106: #define B_HEAD 0x040000 /* a buffer header, not a buffer */
107: #define B_SPARE1 0x080000
108: #define B_BAD 0x100000 /* bad block revectoring in progress */
109: #define B_SPARE2 0xe00000
110: #define B_PRI 0xff000000 /* i/o priority */
111:
112: #define B_PRISHIFT 24
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