1 /*
2  * Memory-only VtBlock cache.
3  *
4  * The cached Venti blocks are in the hash chains.
5  * The cached local blocks are only in the blocks array.
6  * The free blocks are in the heap, which is supposed to
7  * be indexed by second-to-last use but actually
8  * appears to be last use.
9  */
10 
11 #include <u.h>
12 #include <libc.h>
13 #include <venti.h>
14 
15 int nread, ncopy, nwrite;
16 
17 enum {
18 	BioLocal = 1,
19 	BioVenti,
20 	BioReading,
21 	BioWriting,
22 	BioEmpty,
23 	BioVentiError,
24 };
25 enum {
26 	BadHeap = ~0,
27 };
28 struct VtCache
29 {
30 	QLock	lk;
31 	VtConn	*z;
32 	u32int	blocksize;
33 	u32int	now;		/* ticks for usage time stamps */
34 	VtBlock	**hash;	/* hash table for finding addresses */
35 	int		nhash;
36 	VtBlock	**heap;	/* heap for finding victims */
37 	int		nheap;
38 	VtBlock	*block;	/* all allocated blocks */
39 	int		nblock;
40 	uchar	*mem;	/* memory for all blocks and data */
41 	int		(*write)(VtConn*, uchar[VtScoreSize], uint, uchar*, int);
42 };
43 
44 static void cachecheck(VtCache*);
45 
46 VtCache*
47 vtcachealloc(VtConn *z, int blocksize, ulong nblock)
48 {
49 	uchar *p;
50 	VtCache *c;
51 	int i;
52 	VtBlock *b;
53 
54 	c = vtmallocz(sizeof(VtCache));
55 
56 	c->z = z;
57 	c->blocksize = (blocksize + 127) & ~127;
58 	c->nblock = nblock;
59 	c->nhash = nblock;
60 	c->hash = vtmallocz(nblock*sizeof(VtBlock*));
61 	c->heap = vtmallocz(nblock*sizeof(VtBlock*));
62 	c->block = vtmallocz(nblock*sizeof(VtBlock));
63 	c->mem = vtmallocz(nblock*c->blocksize);
64 	c->write = vtwrite;
65 
66 	p = c->mem;
67 	for(i=0; i<nblock; i++){
68 		b = &c->block[i];
69 		b->addr = NilBlock;
70 		b->c = c;
71 		b->data = p;
72 		b->heap = i;
73 		c->heap[i] = b;
74 		p += c->blocksize;
75 	}
76 	c->nheap = nblock;
77 	cachecheck(c);
78 	return c;
79 }
80 
81 /*
82  * BUG This is here so that vbackup can override it and do some
83  * pipelining of writes.  Arguably vtwrite or vtwritepacket or the
84  * cache itself should be providing this functionality.
85  */
86 void
87 vtcachesetwrite(VtCache *c, int (*write)(VtConn*, uchar[VtScoreSize], uint, uchar*, int))
88 {
89 	if(write == nil)
90 		write = vtwrite;
91 	c->write = write;
92 }
93 
94 void
95 vtcachefree(VtCache *c)
96 {
97 	int i;
98 
99 	qlock(&c->lk);
100 
101 	cachecheck(c);
102 	for(i=0; i<c->nblock; i++)
103 		assert(c->block[i].ref == 0);
104 
105 	vtfree(c->hash);
106 	vtfree(c->heap);
107 	vtfree(c->block);
108 	vtfree(c->mem);
109 	vtfree(c);
110 }
111 
112 static void
113 vtcachedump(VtCache *c)
114 {
115 	int i;
116 	VtBlock *b;
117 
118 	for(i=0; i<c->nblock; i++){
119 		b = &c->block[i];
120 		print("cache block %d: type %d score %V iostate %d addr %d ref %d nlock %d\n",
121 			i, b->type, b->score, b->iostate, b->addr, b->ref, b->nlock);
122 	}
123 }
124 
125 static void
126 cachecheck(VtCache *c)
127 {
128 	u32int size, now;
129 	int i, k, refed;
130 	VtBlock *b;
131 
132 	size = c->blocksize;
133 	now = c->now;
134 
135 	for(i = 0; i < c->nheap; i++){
136 		if(c->heap[i]->heap != i)
137 			sysfatal("mis-heaped at %d: %d", i, c->heap[i]->heap);
138 		if(i > 0 && c->heap[(i - 1) >> 1]->used - now > c->heap[i]->used - now)
139 			sysfatal("bad heap ordering");
140 		k = (i << 1) + 1;
141 		if(k < c->nheap && c->heap[i]->used - now > c->heap[k]->used - now)
142 			sysfatal("bad heap ordering");
143 		k++;
144 		if(k < c->nheap && c->heap[i]->used - now > c->heap[k]->used - now)
145 			sysfatal("bad heap ordering");
146 	}
147 
148 	refed = 0;
149 	for(i = 0; i < c->nblock; i++){
150 		b = &c->block[i];
151 		if(b->data != &c->mem[i * size])
152 			sysfatal("mis-blocked at %d", i);
153 		if(b->ref && b->heap == BadHeap)
154 			refed++;
155 		else if(b->addr != NilBlock)
156 			refed++;
157 	}
158 if(c->nheap + refed != c->nblock){
159 fprint(2, "cachecheck: nheap %d refed %d nblocks %d\n", c->nheap, refed, c->nblock);
160 //vtcachedump(c);
161 }
162 	assert(c->nheap + refed == c->nblock);
163 	refed = 0;
164 	for(i = 0; i < c->nblock; i++){
165 		b = &c->block[i];
166 		if(b->ref){
167 if(1)fprint(2, "a=%ud %V ref=%d\n", b->addr, b->score, b->ref);
168 			refed++;
169 		}
170 	}
171 if(refed > 0)fprint(2, "cachecheck: in used %d\n", refed);
172 }
173 
174 static int
175 upheap(int i, VtBlock *b)
176 {
177 	VtBlock *bb;
178 	u32int now;
179 	int p;
180 	VtCache *c;
181 	
182 	c = b->c;
183 	now = c->now;
184 	for(; i != 0; i = p){
185 		p = (i - 1) >> 1;
186 		bb = c->heap[p];
187 		if(b->used - now >= bb->used - now)
188 			break;
189 		c->heap[i] = bb;
190 		bb->heap = i;
191 	}
192 	c->heap[i] = b;
193 	b->heap = i;
194 
195 	return i;
196 }
197 
198 static int
199 downheap(int i, VtBlock *b)
200 {
201 	VtBlock *bb;
202 	u32int now;
203 	int k;
204 	VtCache *c;
205 	
206 	c = b->c;
207 	now = c->now;
208 	for(; ; i = k){
209 		k = (i << 1) + 1;
210 		if(k >= c->nheap)
211 			break;
212 		if(k + 1 < c->nheap && c->heap[k]->used - now > c->heap[k + 1]->used - now)
213 			k++;
214 		bb = c->heap[k];
215 		if(b->used - now <= bb->used - now)
216 			break;
217 		c->heap[i] = bb;
218 		bb->heap = i;
219 	}
220 	c->heap[i] = b;
221 	b->heap = i;
222 	return i;
223 }
224 
225 /*
226  * Delete a block from the heap.
227  * Called with c->lk held.
228  */
229 static void
230 heapdel(VtBlock *b)
231 {
232 	int i, si;
233 	VtCache *c;
234 
235 	c = b->c;
236 
237 	si = b->heap;
238 	if(si == BadHeap)
239 		return;
240 	b->heap = BadHeap;
241 	c->nheap--;
242 	if(si == c->nheap)
243 		return;
244 	b = c->heap[c->nheap];
245 	i = upheap(si, b);
246 	if(i == si)
247 		downheap(i, b);
248 }
249 
250 /*
251  * Insert a block into the heap.
252  * Called with c->lk held.
253  */
254 static void
255 heapins(VtBlock *b)
256 {
257 	assert(b->heap == BadHeap);
258 	upheap(b->c->nheap++, b);
259 }
260 
261 /*
262  * locate the vtBlock with the oldest second to last use.
263  * remove it from the heap, and fix up the heap.
264  */
265 /* called with c->lk held */
266 static VtBlock*
267 vtcachebumpblock(VtCache *c)
268 {
269 	VtBlock *b;
270 
271 	/*
272 	 * locate the vtBlock with the oldest second to last use.
273 	 * remove it from the heap, and fix up the heap.
274 	 */
275 	if(c->nheap == 0){
276 		vtcachedump(c);
277 		fprint(2, "vtcachebumpblock: no free blocks in vtCache");
278 		abort();
279 	}
280 	b = c->heap[0];
281 	heapdel(b);
282 
283 	assert(b->heap == BadHeap);
284 	assert(b->ref == 0);
285 
286 	/*
287 	 * unchain the vtBlock from hash chain if any
288 	 */
289 	if(b->prev){
290 		*(b->prev) = b->next;
291 		if(b->next)
292 			b->next->prev = b->prev;
293 		b->prev = nil;
294 	}
295 
296  	
297 if(0)fprint(2, "droping %x:%V\n", b->addr, b->score);
298 	/* set vtBlock to a reasonable state */
299 	b->ref = 1;
300 	b->iostate = BioEmpty;
301 	return b;
302 }
303 
304 /*
305  * fetch a local block from the memory cache.
306  * if it's not there, load it, bumping some other Block.
307  * if we're out of free blocks, we're screwed.
308  */
309 VtBlock*
310 vtcachelocal(VtCache *c, u32int addr, int type)
311 {
312 	VtBlock *b;
313 
314 	if(addr >= c->nblock)
315 		sysfatal("vtcachelocal: asked for block #%ud; only %d blocks\n",
316 			addr, c->nblock);
317 
318 	b = &c->block[addr];
319 	if(b->addr == NilBlock || b->iostate != BioLocal)
320 		sysfatal("vtcachelocal: block is not local");
321 
322 	if(b->type != type)
323 		sysfatal("vtcachelocal: block has wrong type %d != %d", b->type, type);
324 
325 	qlock(&c->lk);
326 	b->ref++;
327 	qunlock(&c->lk);
328 
329 	qlock(&b->lk);
330 	b->nlock = 1;
331 	return b;
332 }
333 
334 VtBlock*
335 vtcacheallocblock(VtCache *c, int type)
336 {
337 	VtBlock *b;
338 
339 	qlock(&c->lk);
340 	b = vtcachebumpblock(c);
341 	b->iostate = BioLocal;
342 	b->type = type;
343 	b->addr = b - c->block;
344 	vtzeroextend(type, b->data, 0, c->blocksize);
345 	vtlocaltoglobal(b->addr, b->score);
346 	qunlock(&c->lk);
347 
348 	qlock(&b->lk);
349 	b->nlock = 1;
350 
351 	return b;
352 }
353 
354 /*
355  * fetch a global (Venti) block from the memory cache.
356  * if it's not there, load it, bumping some other block.
357  */
358 VtBlock*
359 vtcacheglobal(VtCache *c, uchar score[VtScoreSize], int type)
360 {
361 	VtBlock *b;
362 	ulong h;
363 	int n;
364 	u32int addr;
365 
366 	addr = vtglobaltolocal(score);
367 	if(addr != NilBlock)
368 		return vtcachelocal(c, addr, type);
369 
370 	h = (u32int)(score[0]|(score[1]<<8)|(score[2]<<16)|(score[3]<<24)) % c->nhash;
371 
372 	/*
373 	 * look for the block in the cache
374 	 */
375 	qlock(&c->lk);
376 	for(b = c->hash[h]; b != nil; b = b->next){
377 		if(b->addr != NilBlock || memcmp(b->score, score, VtScoreSize) != 0 || b->type != type)
378 			continue;
379 		heapdel(b);
380 		b->ref++;
381 		qunlock(&c->lk);
382 		qlock(&b->lk);
383 		b->nlock = 1;
384 		if(b->iostate == BioVentiError){
385 			if(chattyventi)
386 				fprint(2, "cached read error for %V\n", score);
387 			werrstr("venti i/o error");
388 			vtblockput(b);
389 			return nil;
390 		}
391 		return b;
392 	}
393 
394 	/*
395 	 * not found
396 	 */
397 	b = vtcachebumpblock(c);
398 	b->addr = NilBlock;
399 	b->type = type;
400 	memmove(b->score, score, VtScoreSize);
401 	/* chain onto correct hash */
402 	b->next = c->hash[h];
403 	c->hash[h] = b;
404 	if(b->next != nil)
405 		b->next->prev = &b->next;
406 	b->prev = &c->hash[h];
407 
408 	/*
409 	 * Lock b before unlocking c, so that others wait while we read.
410 	 * 
411 	 * You might think there is a race between this qlock(b) before qunlock(c)
412 	 * and the qlock(c) while holding a qlock(b) in vtblockwrite.  However,
413 	 * the block here can never be the block in a vtblockwrite, so we're safe.
414 	 * We're certainly living on the edge.
415 	 */
416 	qlock(&b->lk);
417 	b->nlock = 1;
418 	qunlock(&c->lk);
419 
420 	n = vtread(c->z, score, type, b->data, c->blocksize);
421 	if(n < 0){
422 		werrstr("vtread %V: %r", score);
423 		if(chattyventi)
424 			fprint(2, "read %V: %r\n", score);
425 		b->iostate = BioVentiError;
426 		vtblockput(b);
427 		return nil;
428 	}
429 	vtzeroextend(type, b->data, n, c->blocksize);
430 	b->iostate = BioVenti;
431 	b->nlock = 1;
432 	return b;
433 }
434 
435 /*
436  * The thread that has locked b may refer to it by
437  * multiple names.  Nlock counts the number of
438  * references the locking thread holds.  It will call
439  * vtblockput once per reference.
440  */
441 void
442 vtblockduplock(VtBlock *b)
443 {
444 	assert(b->nlock > 0);
445 	b->nlock++;
446 }
447 
448 /*
449  * we're done with the block.
450  * unlock it.  can't use it after calling this.
451  */
452 void
453 vtblockput(VtBlock* b)
454 {
455 	VtCache *c;
456 
457 	if(b == nil)
458 		return;
459 
460 if(0)fprint(2, "vtblockput: %d: %x %d %d\n", getpid(), b->addr, c->nheap, b->iostate);
461 
462 	if(--b->nlock > 0)
463 		return;
464 
465 	/*
466 	 * b->nlock should probably stay at zero while
467 	 * the vtBlock is unlocked, but diskThread and vtSleep
468 	 * conspire to assume that they can just qlock(&b->lk); vtblockput(b),
469 	 * so we have to keep b->nlock set to 1 even 
470 	 * when the vtBlock is unlocked.
471 	 */
472 	assert(b->nlock == 0);
473 	b->nlock = 1;
474 
475 	qunlock(&b->lk);
476 	c = b->c;
477 	qlock(&c->lk);
478 
479 	if(--b->ref > 0){
480 		qunlock(&c->lk);
481 		return;
482 	}
483 
484 	assert(b->ref == 0);
485 	switch(b->iostate){
486 	case BioVenti:
487 //if(b->addr != NilBlock) print("blockput %d\n", b->addr);
488 		b->used = c->now++;
489 	case BioVentiError:
490 		heapins(b);
491 		break;
492 	case BioLocal:
493 		break;
494 	}
495 	qunlock(&c->lk);
496 }
497 
498 int
499 vtblockwrite(VtBlock *b)
500 {
501 	uchar score[VtScoreSize];
502 	VtCache *c;
503 	uint h;
504 	int n;
505 
506 	if(b->iostate != BioLocal){
507 		werrstr("vtblockwrite: not a local block");
508 		return -1;
509 	}
510 
511 	c = b->c;
512 	n = vtzerotruncate(b->type, b->data, c->blocksize);
513 	if(c->write(c->z, score, b->type, b->data, n) < 0)
514 		return -1;
515 
516 	memmove(b->score, score, VtScoreSize);
517 
518 	qlock(&c->lk);
519 	b->iostate = BioVenti;
520 	h = (u32int)(score[0]|(score[1]<<8)|(score[2]<<16)|(score[3]<<24)) % c->nhash;
521 	b->next = c->hash[h];
522 	c->hash[h] = b;
523 	if(b->next != nil)
524 		b->next->prev = &b->next;
525 	b->prev = &c->hash[h];
526 	qunlock(&c->lk);
527 	return 0;
528 }
529 
530 uint
531 vtcacheblocksize(VtCache *c)
532 {
533 	return c->blocksize;
534 }
535 
536 VtBlock*
537 vtblockcopy(VtBlock *b)
538 {
539 	VtBlock *bb;
540 
541 ncopy++;
542 	bb = vtcacheallocblock(b->c, b->type);
543 	if(bb == nil){
544 		vtblockput(b);
545 		return nil;
546 	}
547 	memmove(bb->data, b->data, b->c->blocksize);
548 	vtblockput(b);
549 	return bb;
550 }
551 
552 void
553 vtlocaltoglobal(u32int addr, uchar score[VtScoreSize])
554 {
555 	memset(score, 0, 16);
556 	score[16] = addr>>24;
557 	score[17] = addr>>16;
558 	score[18] = addr>>8;
559 	score[19] = addr;
560 }
561 
562 
563 u32int
564 vtglobaltolocal(uchar score[VtScoreSize])
565 {
566 	static uchar zero[16];
567 	if(memcmp(score, zero, 16) != 0)
568 		return NilBlock;
569 	return (score[16]<<24)|(score[17]<<16)|(score[18]<<8)|score[19];
570 }
571