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1.1 root 1: /*
2: * 'buffer.c' implements the buffer-cache functions. Race-conditions have
3: * been avoided by NEVER letting a interrupt change a buffer (except for the
4: * data, of course), but instead letting the caller do it. NOTE! As interrupts
5: * can wake up a caller, some cli-sti sequences are needed to check for
6: * sleep-on-calls. These should be extremely quick, though (I hope).
7: */
8:
9: #include <linux/config.h>
10: #include <linux/sched.h>
11: #include <linux/kernel.h>
12: #include <asm/system.h>
13:
14: #if (BUFFER_END & 0xfff)
15: #error "Bad BUFFER_END value"
16: #endif
17:
18: #if (BUFFER_END > 0xA0000 && BUFFER_END <= 0x100000)
19: #error "Bad BUFFER_END value"
20: #endif
21:
22: extern int end;
23: struct buffer_head * start_buffer = (struct buffer_head *) &end;
24: struct buffer_head * hash_table[NR_HASH];
25: static struct buffer_head * free_list;
26: static struct task_struct * buffer_wait = NULL;
27: int NR_BUFFERS = 0;
28:
29: static inline void wait_on_buffer(struct buffer_head * bh)
30: {
31: cli();
32: while (bh->b_lock)
33: sleep_on(&bh->b_wait);
34: sti();
35: }
36:
37: int sys_sync(void)
38: {
39: int i;
40: struct buffer_head * bh;
41:
42: sync_inodes(); /* write out inodes into buffers */
43: bh = start_buffer;
44: for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
45: wait_on_buffer(bh);
46: if (bh->b_dirt)
47: ll_rw_block(WRITE,bh);
48: }
49: return 0;
50: }
51:
52: static int sync_dev(int dev)
53: {
54: int i;
55: struct buffer_head * bh;
56:
57: bh = start_buffer;
58: for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
59: if (bh->b_dev != dev)
60: continue;
61: wait_on_buffer(bh);
62: if (bh->b_dirt)
63: ll_rw_block(WRITE,bh);
64: }
65: return 0;
66: }
67:
68: #define _hashfn(dev,block) (((unsigned)(dev^block))%NR_HASH)
69: #define hash(dev,block) hash_table[_hashfn(dev,block)]
70:
71: static inline void remove_from_queues(struct buffer_head * bh)
72: {
73: /* remove from hash-queue */
74: if (bh->b_next)
75: bh->b_next->b_prev = bh->b_prev;
76: if (bh->b_prev)
77: bh->b_prev->b_next = bh->b_next;
78: if (hash(bh->b_dev,bh->b_blocknr) == bh)
79: hash(bh->b_dev,bh->b_blocknr) = bh->b_next;
80: /* remove from free list */
81: if (!(bh->b_prev_free) || !(bh->b_next_free))
82: panic("Free block list corrupted");
83: bh->b_prev_free->b_next_free = bh->b_next_free;
84: bh->b_next_free->b_prev_free = bh->b_prev_free;
85: if (free_list == bh)
86: free_list = bh->b_next_free;
87: }
88:
89: static inline void insert_into_queues(struct buffer_head * bh)
90: {
91: /* put at end of free list */
92: bh->b_next_free = free_list;
93: bh->b_prev_free = free_list->b_prev_free;
94: free_list->b_prev_free->b_next_free = bh;
95: free_list->b_prev_free = bh;
96: /* put the buffer in new hash-queue if it has a device */
97: bh->b_prev = NULL;
98: bh->b_next = NULL;
99: if (!bh->b_dev)
100: return;
101: bh->b_next = hash(bh->b_dev,bh->b_blocknr);
102: hash(bh->b_dev,bh->b_blocknr) = bh;
103: bh->b_next->b_prev = bh;
104: }
105:
106: static struct buffer_head * find_buffer(int dev, int block)
107: {
108: struct buffer_head * tmp;
109:
110: for (tmp = hash(dev,block) ; tmp != NULL ; tmp = tmp->b_next)
111: if (tmp->b_dev==dev && tmp->b_blocknr==block)
112: return tmp;
113: return NULL;
114: }
115:
116: /*
117: * Why like this, I hear you say... The reason is race-conditions.
118: * As we don't lock buffers (unless we are readint them, that is),
119: * something might happen to it while we sleep (ie a read-error
120: * will force it bad). This shouldn't really happen currently, but
121: * the code is ready.
122: */
123: struct buffer_head * get_hash_table(int dev, int block)
124: {
125: struct buffer_head * bh;
126:
127: repeat:
128: if (!(bh=find_buffer(dev,block)))
129: return NULL;
130: bh->b_count++;
131: wait_on_buffer(bh);
132: if (bh->b_dev != dev || bh->b_blocknr != block) {
133: brelse(bh);
134: goto repeat;
135: }
136: return bh;
137: }
138:
139: /*
140: * Ok, this is getblk, and it isn't very clear, again to hinder
141: * race-conditions. Most of the code is seldom used, (ie repeating),
142: * so it should be much more efficient than it looks.
143: */
144: struct buffer_head * getblk(int dev,int block)
145: {
146: struct buffer_head * tmp;
147:
148: repeat:
149: if (tmp=get_hash_table(dev,block))
150: return tmp;
151: tmp = free_list;
152: do {
153: if (!tmp->b_count) {
154: wait_on_buffer(tmp); /* we still have to wait */
155: if (!tmp->b_count) /* on it, it might be dirty */
156: break;
157: }
158: tmp = tmp->b_next_free;
159: } while (tmp != free_list || (tmp=NULL));
160: /* Kids, don't try THIS at home ^^^^^. Magic */
161: if (!tmp) {
162: printk("Sleeping on free buffer ..");
163: sleep_on(&buffer_wait);
164: printk("ok\n");
165: goto repeat;
166: }
167: tmp->b_count++;
168: remove_from_queues(tmp);
169: /*
170: * Now, when we know nobody can get to this node (as it's removed from the
171: * free list), we write it out. We can sleep here without fear of race-
172: * conditions.
173: */
174: if (tmp->b_dirt)
175: sync_dev(tmp->b_dev);
176: /* update buffer contents */
177: tmp->b_dev=dev;
178: tmp->b_blocknr=block;
179: tmp->b_dirt=0;
180: tmp->b_uptodate=0;
181: /* NOTE!! While we possibly slept in sync_dev(), somebody else might have
182: * added "this" block already, so check for that. Thank God for goto's.
183: */
184: if (find_buffer(dev,block)) {
185: tmp->b_dev=0; /* ok, someone else has beaten us */
186: tmp->b_blocknr=0; /* to it - free this block and */
187: tmp->b_count=0; /* try again */
188: insert_into_queues(tmp);
189: goto repeat;
190: }
191: /* and then insert into correct position */
192: insert_into_queues(tmp);
193: return tmp;
194: }
195:
196: void brelse(struct buffer_head * buf)
197: {
198: if (!buf)
199: return;
200: wait_on_buffer(buf);
201: if (!(buf->b_count--))
202: panic("Trying to free free buffer");
203: wake_up(&buffer_wait);
204: }
205:
206: /*
207: * bread() reads a specified block and returns the buffer that contains
208: * it. It returns NULL if the block was unreadable.
209: */
210: struct buffer_head * bread(int dev,int block)
211: {
212: struct buffer_head * bh;
213:
214: if (!(bh=getblk(dev,block)))
215: panic("bread: getblk returned NULL\n");
216: if (bh->b_uptodate)
217: return bh;
218: ll_rw_block(READ,bh);
219: if (bh->b_uptodate)
220: return bh;
221: brelse(bh);
222: return (NULL);
223: }
224:
225: void buffer_init(void)
226: {
227: struct buffer_head * h = start_buffer;
228: void * b = (void *) BUFFER_END;
229: int i;
230:
231: while ( (b -= BLOCK_SIZE) >= ((void *) (h+1)) ) {
232: h->b_dev = 0;
233: h->b_dirt = 0;
234: h->b_count = 0;
235: h->b_lock = 0;
236: h->b_uptodate = 0;
237: h->b_wait = NULL;
238: h->b_next = NULL;
239: h->b_prev = NULL;
240: h->b_data = (char *) b;
241: h->b_prev_free = h-1;
242: h->b_next_free = h+1;
243: h++;
244: NR_BUFFERS++;
245: if (b == (void *) 0x100000)
246: b = (void *) 0xA0000;
247: }
248: h--;
249: free_list = start_buffer;
250: free_list->b_prev_free = h;
251: h->b_next_free = free_list;
252: for (i=0;i<NR_HASH;i++)
253: hash_table[i]=NULL;
254: }
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