Repository navigation
Expand file tree
/
Copy pathbio.c
More file actions
139 lines (120 loc) · 3.19 KB
/
Copy pathbio.c
File metadata and controls
139 lines (120 loc) · 3.19 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
// Buffer cache.
//
// The buffer cache is a linked list of buf structures holding
// cached copies of disk block contents. Caching disk blocks
// in memory reduces the number of disk reads and also provides
// a synchronization point for disk blocks used by multiple processes.
//
// Interface:
// * To get a buffer for a particular disk block, call bread.
// * After changing buffer data, call bwrite to write it to disk.
// * When done with the buffer, call brelse.
// * Do not use the buffer after calling brelse.
// * Only one process at a time can use a buffer,
// so do not keep them longer than necessary.
//
// The implementation uses three state flags internally:
// * B_BUSY: the block has been returned from bread
// and has not been passed back to brelse.
// * B_VALID: the buffer data has been read from the disk.
// * B_DIRTY: the buffer data has been modified
// and needs to be written to disk.
#include "types.h"
#include "defs.h"
#include "param.h"
#include "spinlock.h"
#include "buf.h"
struct {
struct spinlock lock;
struct buf buf[NBUF];
// Linked list of all buffers, through prev/next.
// head.next is most recently used.
struct buf head;
} bcache;
void
binit(void)
{
struct buf *b;
initlock(&bcache.lock, "bcache");
//PAGEBREAK!
// Create linked list of buffers
bcache.head.prev = &bcache.head;
bcache.head.next = &bcache.head;
for(b = bcache.buf; b < bcache.buf+NBUF; b++){
b->next = bcache.head.next;
b->prev = &bcache.head;
b->dev = -1;
bcache.head.next->prev = b;
bcache.head.next = b;
}
}
// Look through buffer cache for sector on device dev.
// If not found, allocate fresh block.
// In either case, return B_BUSY buffer.
static struct buf*
bget(uint dev, uint sector)
{
struct buf *b;
acquire(&bcache.lock);
loop:
// Is the sector already cached?
for(b = bcache.head.next; b != &bcache.head; b = b->next){
if(b->dev == dev && b->sector == sector){
if(!(b->flags & B_BUSY)){
b->flags |= B_BUSY;
release(&bcache.lock);
return b;
}
sleep(b, &bcache.lock);
goto loop;
}
}
// Not cached; recycle some non-busy and clean buffer.
for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
if((b->flags & B_BUSY) == 0 && (b->flags & B_DIRTY) == 0){
b->dev = dev;
b->sector = sector;
b->flags = B_BUSY;
release(&bcache.lock);
return b;
}
}
panic("bget: no buffers");
}
// Return a B_BUSY buf with the contents of the indicated disk sector.
struct buf*
bread(uint dev, uint sector)
{
struct buf *b;
b = bget(dev, sector);
if(!(b->flags & B_VALID))
iderw(b);
return b;
}
// Write b's contents to disk. Must be B_BUSY.
void
bwrite(struct buf *b)
{
if((b->flags & B_BUSY) == 0)
panic("bwrite");
b->flags |= B_DIRTY;
iderw(b);
}
// Release a B_BUSY buffer.
// Move to the head of the MRU list.
void
brelse(struct buf *b)
{
if((b->flags & B_BUSY) == 0)
panic("brelse");
acquire(&bcache.lock);
b->next->prev = b->prev;
b->prev->next = b->next;
b->next = bcache.head.next;
b->prev = &bcache.head;
bcache.head.next->prev = b;
bcache.head.next = b;
b->flags &= ~B_BUSY;
wakeup(b);
release(&bcache.lock);
}