xref: /dragonfly/sys/vfs/hammer2/hammer2_freemap.c (revision 4d4ae2fa)
1 /*
2  * Copyright (c) 2011-2014 The DragonFly Project.  All rights reserved.
3  *
4  * This code is derived from software contributed to The DragonFly Project
5  * by Matthew Dillon <dillon@dragonflybsd.org>
6  * by Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  *
12  * 1. Redistributions of source code must retain the above copyright
13  *    notice, this list of conditions and the following disclaimer.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice, this list of conditions and the following disclaimer in
16  *    the documentation and/or other materials provided with the
17  *    distribution.
18  * 3. Neither the name of The DragonFly Project nor the names of its
19  *    contributors may be used to endorse or promote products derived
20  *    from this software without specific, prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
23  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
24  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
25  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
26  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
27  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
28  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
29  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
30  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
31  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
32  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33  * SUCH DAMAGE.
34  */
35 #include <sys/param.h>
36 #include <sys/systm.h>
37 #include <sys/kernel.h>
38 #include <sys/fcntl.h>
39 #include <sys/buf.h>
40 #include <sys/proc.h>
41 #include <sys/namei.h>
42 #include <sys/mount.h>
43 #include <sys/vnode.h>
44 #include <sys/mountctl.h>
45 
46 #include "hammer2.h"
47 
48 #define FREEMAP_DEBUG	0
49 
50 struct hammer2_fiterate {
51 	hammer2_off_t	bpref;
52 	hammer2_off_t	bnext;
53 	int		loops;
54 };
55 
56 typedef struct hammer2_fiterate hammer2_fiterate_t;
57 
58 static int hammer2_freemap_try_alloc(hammer2_chain_t **parentp,
59 			hammer2_blockref_t *bref, int radix,
60 			hammer2_fiterate_t *iter, hammer2_tid_t mtid);
61 static void hammer2_freemap_init(hammer2_dev_t *hmp,
62 			hammer2_key_t key, hammer2_chain_t *chain);
63 static int hammer2_bmap_alloc(hammer2_dev_t *hmp,
64 			hammer2_bmap_data_t *bmap, uint16_t class,
65 			int n, int radix, hammer2_key_t *basep);
66 static int hammer2_freemap_iterate(hammer2_chain_t **parentp,
67 			hammer2_chain_t **chainp,
68 			hammer2_fiterate_t *iter);
69 
70 static __inline
71 int
72 hammer2_freemapradix(int radix)
73 {
74 	return(radix);
75 }
76 
77 /*
78  * Calculate the device offset for the specified FREEMAP_NODE or FREEMAP_LEAF
79  * bref.  Return a combined media offset and physical size radix.  Freemap
80  * chains use fixed storage offsets in the 4MB reserved area at the
81  * beginning of each 2GB zone
82  *
83  * Rotate between four possibilities.  Theoretically this means we have three
84  * good freemaps in case of a crash which we can use as a base for the fixup
85  * scan at mount-time.
86  */
87 #define H2FMBASE(key, radix)	((key) & ~(((hammer2_off_t)1 << (radix)) - 1))
88 #define H2FMSHIFT(radix)	((hammer2_off_t)1 << (radix))
89 
90 static
91 int
92 hammer2_freemap_reserve(hammer2_chain_t *chain, int radix)
93 {
94 	hammer2_blockref_t *bref = &chain->bref;
95 	hammer2_off_t off;
96 	int index;
97 	int index_inc;
98 	size_t bytes;
99 
100 	/*
101 	 * Physical allocation size.
102 	 */
103 	bytes = (size_t)1 << radix;
104 
105 	/*
106 	 * Calculate block selection index 0..7 of current block.  If this
107 	 * is the first allocation of the block (verses a modification of an
108 	 * existing block), we use index 0, otherwise we use the next rotating
109 	 * index.
110 	 */
111 	if ((bref->data_off & ~HAMMER2_OFF_MASK_RADIX) == 0) {
112 		index = 0;
113 	} else {
114 		off = bref->data_off & ~HAMMER2_OFF_MASK_RADIX &
115 		      (((hammer2_off_t)1 <<
116 			HAMMER2_FREEMAP_LEVEL1_RADIX) - 1);
117 		off = off / HAMMER2_PBUFSIZE;
118 		KKASSERT(off >= HAMMER2_ZONE_FREEMAP_00 &&
119 			 off < HAMMER2_ZONE_FREEMAP_END);
120 		index = (int)(off - HAMMER2_ZONE_FREEMAP_00) /
121 			HAMMER2_ZONE_FREEMAP_INC;
122 		KKASSERT(index >= 0 && index < HAMMER2_NFREEMAPS);
123 		if (++index == HAMMER2_NFREEMAPS)
124 			index = 0;
125 	}
126 
127 	/*
128 	 * Calculate the block offset of the reserved block.  This will
129 	 * point into the 4MB reserved area at the base of the appropriate
130 	 * 2GB zone, once added to the FREEMAP_x selection above.
131 	 */
132 	index_inc = index * HAMMER2_ZONE_FREEMAP_INC;
133 
134 	switch(bref->keybits) {
135 	/* case HAMMER2_FREEMAP_LEVEL6_RADIX: not applicable */
136 	case HAMMER2_FREEMAP_LEVEL5_RADIX:	/* 2EB */
137 		KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
138 		KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
139 		off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL5_RADIX) +
140 		      (index_inc + HAMMER2_ZONE_FREEMAP_00 +
141 		       HAMMER2_ZONEFM_LEVEL5) * HAMMER2_PBUFSIZE;
142 		break;
143 	case HAMMER2_FREEMAP_LEVEL4_RADIX:	/* 2EB */
144 		KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
145 		KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
146 		off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL4_RADIX) +
147 		      (index_inc + HAMMER2_ZONE_FREEMAP_00 +
148 		       HAMMER2_ZONEFM_LEVEL4) * HAMMER2_PBUFSIZE;
149 		break;
150 	case HAMMER2_FREEMAP_LEVEL3_RADIX:	/* 2PB */
151 		KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
152 		KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
153 		off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL3_RADIX) +
154 		      (index_inc + HAMMER2_ZONE_FREEMAP_00 +
155 		       HAMMER2_ZONEFM_LEVEL3) * HAMMER2_PBUFSIZE;
156 		break;
157 	case HAMMER2_FREEMAP_LEVEL2_RADIX:	/* 2TB */
158 		KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
159 		KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
160 		off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL2_RADIX) +
161 		      (index_inc + HAMMER2_ZONE_FREEMAP_00 +
162 		       HAMMER2_ZONEFM_LEVEL2) * HAMMER2_PBUFSIZE;
163 		break;
164 	case HAMMER2_FREEMAP_LEVEL1_RADIX:	/* 2GB */
165 		KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_LEAF);
166 		KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
167 		off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
168 		      (index_inc + HAMMER2_ZONE_FREEMAP_00 +
169 		       HAMMER2_ZONEFM_LEVEL1) * HAMMER2_PBUFSIZE;
170 		break;
171 	default:
172 		panic("freemap: bad radix(2) %p %d\n", bref, bref->keybits);
173 		/* NOT REACHED */
174 		off = (hammer2_off_t)-1;
175 		break;
176 	}
177 	bref->data_off = off | radix;
178 #if FREEMAP_DEBUG
179 	kprintf("FREEMAP BLOCK TYPE %d %016jx/%d DATA_OFF=%016jx\n",
180 		bref->type, bref->key, bref->keybits, bref->data_off);
181 #endif
182 	return (0);
183 }
184 
185 /*
186  * Normal freemap allocator
187  *
188  * Use available hints to allocate space using the freemap.  Create missing
189  * freemap infrastructure on-the-fly as needed (including marking initial
190  * allocations using the iterator as allocated, instantiating new 2GB zones,
191  * and dealing with the end-of-media edge case).
192  *
193  * ip and bpref are only used as a heuristic to determine locality of
194  * reference.  bref->key may also be used heuristically.
195  */
196 int
197 hammer2_freemap_alloc(hammer2_chain_t *chain, size_t bytes)
198 {
199 	hammer2_dev_t *hmp = chain->hmp;
200 	hammer2_blockref_t *bref = &chain->bref;
201 	hammer2_chain_t *parent;
202 	hammer2_tid_t mtid;
203 	int radix;
204 	int error;
205 	unsigned int hindex;
206 	hammer2_fiterate_t iter;
207 
208 	mtid = hammer2_trans_sub(hmp->spmp);
209 
210 	/*
211 	 * Validate the allocation size.  It must be a power of 2.
212 	 *
213 	 * For now require that the caller be aware of the minimum
214 	 * allocation (1K).
215 	 */
216 	radix = hammer2_getradix(bytes);
217 	KKASSERT((size_t)1 << radix == bytes);
218 
219 	if (bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
220 	    bref->type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
221 		/*
222 		 * Freemap blocks themselves are assigned from the reserve
223 		 * area, not allocated from the freemap.
224 		 */
225 		error = hammer2_freemap_reserve(chain, radix);
226 		KKASSERT(error == 0);
227 
228 		return error;
229 	}
230 
231 	KKASSERT(bytes >= HAMMER2_ALLOC_MIN && bytes <= HAMMER2_ALLOC_MAX);
232 
233 	/*
234 	 * Calculate the starting point for our allocation search.
235 	 *
236 	 * Each freemap leaf is dedicated to a specific freemap_radix.
237 	 * The freemap_radix can be more fine-grained than the device buffer
238 	 * radix which results in inodes being grouped together in their
239 	 * own segment, terminal-data (16K or less) and initial indirect
240 	 * block being grouped together, and then full-indirect and full-data
241 	 * blocks (64K) being grouped together.
242 	 *
243 	 * The single most important aspect of this is the inode grouping
244 	 * because that is what allows 'find' and 'ls' and other filesystem
245 	 * topology operations to run fast.
246 	 */
247 #if 0
248 	if (bref->data_off & ~HAMMER2_OFF_MASK_RADIX)
249 		bpref = bref->data_off & ~HAMMER2_OFF_MASK_RADIX;
250 	else if (trans->tmp_bpref)
251 		bpref = trans->tmp_bpref;
252 	else if (trans->tmp_ip)
253 		bpref = trans->tmp_ip->chain->bref.data_off;
254 	else
255 #endif
256 	/*
257 	 * Heuristic tracking index.  We would like one for each distinct
258 	 * bref type if possible.  heur_freemap[] has room for two classes
259 	 * for each type.  At a minimum we have to break-up our heuristic
260 	 * by device block sizes.
261 	 */
262 	hindex = hammer2_devblkradix(radix) - HAMMER2_MINIORADIX;
263 	KKASSERT(hindex < HAMMER2_FREEMAP_HEUR_NRADIX);
264 	hindex += bref->type * HAMMER2_FREEMAP_HEUR_NRADIX;
265 	hindex &= HAMMER2_FREEMAP_HEUR_TYPES * HAMMER2_FREEMAP_HEUR_NRADIX - 1;
266 	KKASSERT(hindex < HAMMER2_FREEMAP_HEUR_SIZE);
267 
268 	iter.bpref = hmp->heur_freemap[hindex];
269 
270 	/*
271 	 * Make sure bpref is in-bounds.  It's ok if bpref covers a zone's
272 	 * reserved area, the try code will iterate past it.
273 	 */
274 	if (iter.bpref > hmp->voldata.volu_size)
275 		iter.bpref = hmp->voldata.volu_size - 1;
276 
277 	/*
278 	 * Iterate the freemap looking for free space before and after.
279 	 */
280 	parent = &hmp->fchain;
281 	hammer2_chain_ref(parent);
282 	hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
283 	error = EAGAIN;
284 	iter.bnext = iter.bpref;
285 	iter.loops = 0;
286 
287 	while (error == EAGAIN) {
288 		error = hammer2_freemap_try_alloc(&parent, bref, radix,
289 						  &iter, mtid);
290 	}
291 	hmp->heur_freemap[hindex] = iter.bnext;
292 	hammer2_chain_unlock(parent);
293 	hammer2_chain_drop(parent);
294 
295 	KKASSERT(error == 0);
296 
297 	return (error);
298 }
299 
300 static int
301 hammer2_freemap_try_alloc(hammer2_chain_t **parentp,
302 			  hammer2_blockref_t *bref, int radix,
303 			  hammer2_fiterate_t *iter, hammer2_tid_t mtid)
304 {
305 	hammer2_dev_t *hmp = (*parentp)->hmp;
306 	hammer2_off_t l0size;
307 	hammer2_off_t l1size;
308 	hammer2_off_t l1mask;
309 	hammer2_key_t key_dummy;
310 	hammer2_chain_t *chain;
311 	hammer2_off_t key;
312 	size_t bytes;
313 	uint16_t class;
314 	int error = 0;
315 	int cache_index = -1;
316 
317 	/*
318 	 * Calculate the number of bytes being allocated, the number
319 	 * of contiguous bits of bitmap being allocated, and the bitmap
320 	 * mask.
321 	 *
322 	 * WARNING! cpu hardware may mask bits == 64 -> 0 and blow up the
323 	 *	    mask calculation.
324 	 */
325 	bytes = (size_t)1 << radix;
326 	class = (bref->type << 8) | hammer2_devblkradix(radix);
327 
328 	/*
329 	 * Lookup the level1 freemap chain, creating and initializing one
330 	 * if necessary.  Intermediate levels will be created automatically
331 	 * when necessary by hammer2_chain_create().
332 	 */
333 	key = H2FMBASE(iter->bnext, HAMMER2_FREEMAP_LEVEL1_RADIX);
334 	l0size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
335 	l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
336 	l1mask = l1size - 1;
337 
338 	chain = hammer2_chain_lookup(parentp, &key_dummy, key, key + l1mask,
339 				     &cache_index,
340 				     HAMMER2_LOOKUP_ALWAYS |
341 				     HAMMER2_LOOKUP_MATCHIND);
342 
343 	if (chain == NULL) {
344 		/*
345 		 * Create the missing leaf, be sure to initialize
346 		 * the auxillary freemap tracking information in
347 		 * the bref.check.freemap structure.
348 		 */
349 #if 0
350 		kprintf("freemap create L1 @ %016jx bpref %016jx\n",
351 			key, iter->bpref);
352 #endif
353 		error = hammer2_chain_create(parentp, &chain,
354 				     hmp->spmp, HAMMER2_METH_DEFAULT,
355 				     key, HAMMER2_FREEMAP_LEVEL1_RADIX,
356 				     HAMMER2_BREF_TYPE_FREEMAP_LEAF,
357 				     HAMMER2_FREEMAP_LEVELN_PSIZE,
358 				     mtid, 0, 0);
359 		KKASSERT(error == 0);
360 		if (error == 0) {
361 			hammer2_chain_modify(chain, mtid, 0, 0);
362 			bzero(&chain->data->bmdata[0],
363 			      HAMMER2_FREEMAP_LEVELN_PSIZE);
364 			chain->bref.check.freemap.bigmask = (uint32_t)-1;
365 			chain->bref.check.freemap.avail = l1size;
366 			/* bref.methods should already be inherited */
367 
368 			hammer2_freemap_init(hmp, key, chain);
369 		}
370 	} else if (chain->error) {
371 		/*
372 		 * Error during lookup.
373 		 */
374 		kprintf("hammer2_freemap_try_alloc: %016jx: error %s\n",
375 			(intmax_t)bref->data_off,
376 			hammer2_error_str(chain->error));
377 		error = EIO;
378 	} else if ((chain->bref.check.freemap.bigmask &
379 		   ((size_t)1 << radix)) == 0) {
380 		/*
381 		 * Already flagged as not having enough space
382 		 */
383 		error = ENOSPC;
384 	} else {
385 		/*
386 		 * Modify existing chain to setup for adjustment.
387 		 */
388 		hammer2_chain_modify(chain, mtid, 0, 0);
389 	}
390 
391 	/*
392 	 * Scan 2MB entries.
393 	 */
394 	if (error == 0) {
395 		hammer2_bmap_data_t *bmap;
396 		hammer2_key_t base_key;
397 		int count;
398 		int start;
399 		int n;
400 
401 		KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF);
402 		start = (int)((iter->bnext - key) >>
403 			      HAMMER2_FREEMAP_LEVEL0_RADIX);
404 		KKASSERT(start >= 0 && start < HAMMER2_FREEMAP_COUNT);
405 		hammer2_chain_modify(chain, mtid, 0, 0);
406 
407 		error = ENOSPC;
408 		for (count = 0; count < HAMMER2_FREEMAP_COUNT; ++count) {
409 			int availchk;
410 
411 			if (start + count >= HAMMER2_FREEMAP_COUNT &&
412 			    start - count < 0) {
413 				break;
414 			}
415 
416 			/*
417 			 * Calculate bmap pointer
418 			 *
419 			 * NOTE: bmap pointer is invalid if n >= FREEMAP_COUNT.
420 			 */
421 			n = start + count;
422 			bmap = &chain->data->bmdata[n];
423 
424 			if (n >= HAMMER2_FREEMAP_COUNT) {
425 				availchk = 0;
426 			} else if (bmap->avail) {
427 				availchk = 1;
428 			} else if (radix < HAMMER2_FREEMAP_BLOCK_RADIX &&
429 			          (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK)) {
430 				availchk = 1;
431 			} else {
432 				availchk = 0;
433 			}
434 
435 			if (availchk &&
436 			    (bmap->class == 0 || bmap->class == class)) {
437 				base_key = key + n * l0size;
438 				error = hammer2_bmap_alloc(hmp, bmap,
439 							   class, n, radix,
440 							   &base_key);
441 				if (error != ENOSPC) {
442 					key = base_key;
443 					break;
444 				}
445 			}
446 
447 			/*
448 			 * Must recalculate after potentially having called
449 			 * hammer2_bmap_alloc() above in case chain was
450 			 * reallocated.
451 			 *
452 			 * NOTE: bmap pointer is invalid if n < 0.
453 			 */
454 			n = start - count;
455 			bmap = &chain->data->bmdata[n];
456 			if (n < 0) {
457 				availchk = 0;
458 			} else if (bmap->avail) {
459 				availchk = 1;
460 			} else if (radix < HAMMER2_FREEMAP_BLOCK_RADIX &&
461 			          (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK)) {
462 				availchk = 1;
463 			} else {
464 				availchk = 0;
465 			}
466 
467 			if (availchk &&
468 			    (bmap->class == 0 || bmap->class == class)) {
469 				base_key = key + n * l0size;
470 				error = hammer2_bmap_alloc(hmp, bmap,
471 							   class, n, radix,
472 							   &base_key);
473 				if (error != ENOSPC) {
474 					key = base_key;
475 					break;
476 				}
477 			}
478 		}
479 		if (error == ENOSPC) {
480 			chain->bref.check.freemap.bigmask &=
481 				(uint32_t)~((size_t)1 << radix);
482 		}
483 		/* XXX also scan down from original count */
484 	}
485 
486 	if (error == 0) {
487 		/*
488 		 * Assert validity.  Must be beyond the static allocator used
489 		 * by newfs_hammer2 (and thus also beyond the aux area),
490 		 * not go past the volume size, and must not be in the
491 		 * reserved segment area for a zone.
492 		 */
493 		KKASSERT(key >= hmp->voldata.allocator_beg &&
494 			 key + bytes <= hmp->voldata.volu_size);
495 		KKASSERT((key & HAMMER2_ZONE_MASK64) >= HAMMER2_ZONE_SEG);
496 		bref->data_off = key | radix;
497 #if 0
498 		kprintf("alloc cp=%p %016jx %016jx using %016jx\n",
499 			chain,
500 			bref->key, bref->data_off, chain->bref.data_off);
501 #endif
502 	} else if (error == ENOSPC) {
503 		/*
504 		 * Return EAGAIN with next iteration in iter->bnext, or
505 		 * return ENOSPC if the allocation map has been exhausted.
506 		 */
507 		error = hammer2_freemap_iterate(parentp, &chain, iter);
508 	}
509 
510 	/*
511 	 * Cleanup
512 	 */
513 	if (chain) {
514 		hammer2_chain_unlock(chain);
515 		hammer2_chain_drop(chain);
516 	}
517 	return (error);
518 }
519 
520 /*
521  * Allocate (1<<radix) bytes from the bmap whos base data offset is (*basep).
522  *
523  * If the linear iterator is mid-block we use it directly (the bitmap should
524  * already be marked allocated), otherwise we search for a block in the bitmap
525  * that fits the allocation request.
526  *
527  * A partial bitmap allocation sets the minimum bitmap granularity (16KB)
528  * to fully allocated and adjusts the linear allocator to allow the
529  * remaining space to be allocated.
530  */
531 static
532 int
533 hammer2_bmap_alloc(hammer2_dev_t *hmp, hammer2_bmap_data_t *bmap,
534 		   uint16_t class, int n, int radix, hammer2_key_t *basep)
535 {
536 	size_t size;
537 	size_t bgsize;
538 	int bmradix;
539 	hammer2_bitmap_t bmmask;
540 	int offset;
541 	int i;
542 	int j;
543 
544 	/*
545 	 * Take into account 2-bits per block when calculating bmradix.
546 	 */
547 	size = (size_t)1 << radix;
548 
549 	if (radix <= HAMMER2_FREEMAP_BLOCK_RADIX) {
550 		bmradix = 2;
551 		/* (16K) 2 bits per allocation block */
552 	} else {
553 		bmradix = (hammer2_bitmap_t)2 <<
554 			  (radix - HAMMER2_FREEMAP_BLOCK_RADIX);
555 		/* (32K-256K) 4, 8, 16, 32 bits per allocation block */
556 	}
557 
558 	/*
559 	 * Use the linear iterator to pack small allocations, otherwise
560 	 * fall-back to finding a free 16KB chunk.  The linear iterator
561 	 * is only valid when *NOT* on a freemap chunking boundary (16KB).
562 	 * If it is the bitmap must be scanned.  It can become invalid
563 	 * once we pack to the boundary.  We adjust it after a bitmap
564 	 * allocation only for sub-16KB allocations (so the perfectly good
565 	 * previous value can still be used for fragments when 16KB+
566 	 * allocations are made).
567 	 *
568 	 * Beware of hardware artifacts when bmradix == 64 (intermediate
569 	 * result can wind up being '1' instead of '0' if hardware masks
570 	 * bit-count & 31).
571 	 *
572 	 * NOTE: j needs to be even in the j= calculation.  As an artifact
573 	 *	 of the /2 division, our bitmask has to clear bit 0.
574 	 *
575 	 * NOTE: TODO this can leave little unallocatable fragments lying
576 	 *	 around.
577 	 */
578 	if (((uint32_t)bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK) + size <=
579 	    HAMMER2_FREEMAP_BLOCK_SIZE &&
580 	    (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK) &&
581 	    bmap->linear < HAMMER2_SEGSIZE) {
582 		KKASSERT(bmap->linear >= 0 &&
583 			 bmap->linear + size <= HAMMER2_SEGSIZE &&
584 			 (bmap->linear & (HAMMER2_ALLOC_MIN - 1)) == 0);
585 		offset = bmap->linear;
586 		i = offset / (HAMMER2_SEGSIZE / 8);
587 		j = (offset / (HAMMER2_FREEMAP_BLOCK_SIZE / 2)) & 30;
588 		bmmask = (bmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
589 			 HAMMER2_BMAP_ALLONES :
590 			 ((hammer2_bitmap_t)1 << bmradix) - 1;
591 		bmmask <<= j;
592 		bmap->linear = offset + size;
593 	} else {
594 		for (i = 0; i < HAMMER2_BMAP_ELEMENTS; ++i) {
595 			bmmask = (bmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
596 				 HAMMER2_BMAP_ALLONES :
597 				 ((hammer2_bitmap_t)1 << bmradix) - 1;
598 			for (j = 0;
599 			     j < HAMMER2_BMAP_BITS_PER_ELEMENT;
600 			     j += bmradix) {
601 				if ((bmap->bitmapq[i] & bmmask) == 0)
602 					goto success;
603 				bmmask <<= bmradix;
604 			}
605 		}
606 		/*fragments might remain*/
607 		/*KKASSERT(bmap->avail == 0);*/
608 		return (ENOSPC);
609 success:
610 		offset = i * (HAMMER2_SEGSIZE / HAMMER2_BMAP_ELEMENTS) +
611 			 (j * (HAMMER2_FREEMAP_BLOCK_SIZE / 2));
612 		if (size & HAMMER2_FREEMAP_BLOCK_MASK)
613 			bmap->linear = offset + size;
614 	}
615 
616 	/* 8 x (64/2) -> 256 x 16K -> 4MB */
617 	KKASSERT(i >= 0 && i < HAMMER2_BMAP_ELEMENTS);
618 
619 	/*
620 	 * Optimize the buffer cache to avoid unnecessary read-before-write
621 	 * operations.
622 	 *
623 	 * The device block size could be larger than the allocation size
624 	 * so the actual bitmap test is somewhat more involved.  We have
625 	 * to use a compatible buffer size for this operation.
626 	 */
627 	if ((bmap->bitmapq[i] & bmmask) == 0 &&
628 	    hammer2_devblksize(size) != size) {
629 		size_t psize = hammer2_devblksize(size);
630 		hammer2_off_t pmask = (hammer2_off_t)psize - 1;
631 		int pbmradix = (hammer2_bitmap_t)2 <<
632 					(hammer2_devblkradix(radix) -
633 			       HAMMER2_FREEMAP_BLOCK_RADIX);
634 		hammer2_bitmap_t pbmmask;
635 		int pradix = hammer2_getradix(psize);
636 
637 		pbmmask = (pbmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
638 			HAMMER2_BMAP_ALLONES :
639 			((hammer2_bitmap_t)1 << pbmradix) - 1;
640 		while ((pbmmask & bmmask) == 0)
641 			pbmmask <<= pbmradix;
642 
643 #if 0
644 		kprintf("%016jx mask %016jx %016jx %016jx (%zd/%zd)\n",
645 			*basep + offset, bmap->bitmapq[i],
646 			pbmmask, bmmask, size, psize);
647 #endif
648 
649 		if ((bmap->bitmapq[i] & pbmmask) == 0) {
650 			hammer2_io_newq(hmp, HAMMER2_BREF_TYPE_FREEMAP_LEAF,
651 					(*basep + (offset & ~pmask)) |
652 					pradix, psize);
653 		}
654 	}
655 
656 #if 0
657 	/*
658 	 * When initializing a new inode segment also attempt to initialize
659 	 * an adjacent segment.  Be careful not to index beyond the array
660 	 * bounds.
661 	 *
662 	 * We do this to try to localize inode accesses to improve
663 	 * directory scan rates.  XXX doesn't improve scan rates.
664 	 */
665 	if (size == HAMMER2_INODE_BYTES) {
666 		if (n & 1) {
667 			if (bmap[-1].radix == 0 && bmap[-1].avail)
668 				bmap[-1].radix = radix;
669 		} else {
670 			if (bmap[1].radix == 0 && bmap[1].avail)
671 				bmap[1].radix = radix;
672 		}
673 	}
674 #endif
675 	/*
676 	 * Calculate the bitmap-granular change in bgsize for the volume
677 	 * header.  We cannot use the fine-grained change here because
678 	 * the bulkfree code can't undo it.  If the bitmap element is already
679 	 * marked allocated it has already been accounted for.
680 	 */
681 	if (radix < HAMMER2_FREEMAP_BLOCK_RADIX) {
682 		if (bmap->bitmapq[i] & bmmask)
683 			bgsize = 0;
684 		else
685 			bgsize = HAMMER2_FREEMAP_BLOCK_SIZE;
686 	} else {
687 		bgsize = size;
688 	}
689 
690 	/*
691 	 * Adjust the bitmap, set the class (it might have been 0),
692 	 * and available bytes, update the allocation offset (*basep)
693 	 * from the L0 base to the actual offset.
694 	 *
695 	 * avail must reflect the bitmap-granular availability.  The allocator
696 	 * tests will also check the linear iterator.
697 	 */
698 	bmap->bitmapq[i] |= bmmask;
699 	bmap->class = class;
700 	bmap->avail -= bgsize;
701 	*basep += offset;
702 
703 	/*
704 	 * Adjust the volume header's allocator_free parameter.  This
705 	 * parameter has to be fixed up by bulkfree which has no way to
706 	 * figure out sub-16K chunking, so it must be adjusted by the
707 	 * bitmap-granular size.
708 	 */
709 	if (bgsize) {
710 		hammer2_voldata_lock(hmp);
711 		hammer2_voldata_modify(hmp);
712 		hmp->voldata.allocator_free -= bgsize;
713 		hammer2_voldata_unlock(hmp);
714 	}
715 
716 	return(0);
717 }
718 
719 static
720 void
721 hammer2_freemap_init(hammer2_dev_t *hmp, hammer2_key_t key,
722 		     hammer2_chain_t *chain)
723 {
724 	hammer2_off_t l1size;
725 	hammer2_off_t lokey;
726 	hammer2_off_t hikey;
727 	hammer2_bmap_data_t *bmap;
728 	int count;
729 
730 	l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
731 
732 	/*
733 	 * Calculate the portion of the 2GB map that should be initialized
734 	 * as free.  Portions below or after will be initialized as allocated.
735 	 * SEGMASK-align the areas so we don't have to worry about sub-scans
736 	 * or endianess when using memset.
737 	 *
738 	 * (1) Ensure that all statically allocated space from newfs_hammer2
739 	 *     is marked allocated.
740 	 *
741 	 * (2) Ensure that the reserved area is marked allocated (typically
742 	 *     the first 4MB of the 2GB area being represented).
743 	 *
744 	 * (3) Ensure that any trailing space at the end-of-volume is marked
745 	 *     allocated.
746 	 *
747 	 * WARNING! It is possible for lokey to be larger than hikey if the
748 	 *	    entire 2GB segment is within the static allocation.
749 	 */
750 	lokey = (hmp->voldata.allocator_beg + HAMMER2_SEGMASK64) &
751 		~HAMMER2_SEGMASK64;
752 
753 	if (lokey < H2FMBASE(key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
754 		  HAMMER2_ZONE_SEG64) {
755 		lokey = H2FMBASE(key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
756 			HAMMER2_ZONE_SEG64;
757 	}
758 
759 	hikey = key + H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
760 	if (hikey > hmp->voldata.volu_size) {
761 		hikey = hmp->voldata.volu_size & ~HAMMER2_SEGMASK64;
762 	}
763 
764 	chain->bref.check.freemap.avail =
765 		H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
766 	bmap = &chain->data->bmdata[0];
767 
768 	for (count = 0; count < HAMMER2_FREEMAP_COUNT; ++count) {
769 		if (key < lokey || key >= hikey) {
770 			memset(bmap->bitmapq, -1,
771 			       sizeof(bmap->bitmapq));
772 			bmap->avail = 0;
773 			bmap->linear = HAMMER2_SEGSIZE;
774 			chain->bref.check.freemap.avail -=
775 				H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
776 		} else {
777 			bmap->avail = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
778 		}
779 		key += H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
780 		++bmap;
781 	}
782 }
783 
784 /*
785  * The current Level 1 freemap has been exhausted, iterate to the next
786  * one, return ENOSPC if no freemaps remain.
787  *
788  * XXX this should rotate back to the beginning to handle freed-up space
789  * XXX or use intermediate entries to locate free space. TODO
790  */
791 static int
792 hammer2_freemap_iterate(hammer2_chain_t **parentp, hammer2_chain_t **chainp,
793 			hammer2_fiterate_t *iter)
794 {
795 	hammer2_dev_t *hmp = (*parentp)->hmp;
796 
797 	iter->bnext &= ~(H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX) - 1);
798 	iter->bnext += H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
799 	if (iter->bnext >= hmp->voldata.volu_size) {
800 		iter->bnext = 0;
801 		if (++iter->loops == 2)
802 			return (ENOSPC);
803 	}
804 	return(EAGAIN);
805 }
806 
807 /*
808  * Adjust the bit-pattern for data in the freemap bitmap according to
809  * (how).  This code is called from on-mount recovery to fixup (mark
810  * as allocated) blocks whos freemap upates might not have been committed
811  * in the last crash and is used by the bulk freemap scan to stage frees.
812  *
813  * XXX currently disabled when how == 0 (the normal real-time case).  At
814  * the moment we depend on the bulk freescan to actually free blocks.  It
815  * will still call this routine with a non-zero how to stage possible frees
816  * and to do the actual free.
817  */
818 void
819 hammer2_freemap_adjust(hammer2_dev_t *hmp, hammer2_blockref_t *bref,
820 		       int how)
821 {
822 	hammer2_off_t data_off = bref->data_off;
823 	hammer2_chain_t *chain;
824 	hammer2_chain_t *parent;
825 	hammer2_bmap_data_t *bmap;
826 	hammer2_key_t key;
827 	hammer2_key_t key_dummy;
828 	hammer2_off_t l0size;
829 	hammer2_off_t l1size;
830 	hammer2_off_t l1mask;
831 	hammer2_tid_t mtid;
832 	hammer2_bitmap_t *bitmap;
833 	const hammer2_bitmap_t bmmask00 = 0;
834 	hammer2_bitmap_t bmmask01;
835 	hammer2_bitmap_t bmmask10;
836 	hammer2_bitmap_t bmmask11;
837 	size_t bytes;
838 	uint16_t class;
839 	int radix;
840 	int start;
841 	int count;
842 	int modified = 0;
843 	int cache_index = -1;
844 	int error;
845 	size_t bgsize = 0;
846 
847 	KKASSERT(how == HAMMER2_FREEMAP_DORECOVER);
848 
849 	mtid = hammer2_trans_sub(hmp->spmp);
850 
851 	radix = (int)data_off & HAMMER2_OFF_MASK_RADIX;
852 	data_off &= ~HAMMER2_OFF_MASK_RADIX;
853 	KKASSERT(radix <= HAMMER2_RADIX_MAX);
854 
855 	bytes = (size_t)1 << radix;
856 	class = (bref->type << 8) | hammer2_devblkradix(radix);
857 
858 	/*
859 	 * We can't adjust thre freemap for data allocations made by
860 	 * newfs_hammer2.
861 	 */
862 	if (data_off < hmp->voldata.allocator_beg)
863 		return;
864 
865 	KKASSERT((data_off & HAMMER2_ZONE_MASK64) >= HAMMER2_ZONE_SEG);
866 
867 	/*
868 	 * Lookup the level1 freemap chain.  The chain must exist.
869 	 */
870 	key = H2FMBASE(data_off, HAMMER2_FREEMAP_LEVEL1_RADIX);
871 	l0size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
872 	l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
873 	l1mask = l1size - 1;
874 
875 	parent = &hmp->fchain;
876 	hammer2_chain_ref(parent);
877 	hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
878 
879 	chain = hammer2_chain_lookup(&parent, &key_dummy, key, key + l1mask,
880 				     &cache_index,
881 				     HAMMER2_LOOKUP_ALWAYS |
882 				     HAMMER2_LOOKUP_MATCHIND);
883 
884 	/*
885 	 * Stop early if we are trying to free something but no leaf exists.
886 	 */
887 	if (chain == NULL && how != HAMMER2_FREEMAP_DORECOVER) {
888 		kprintf("hammer2_freemap_adjust: %016jx: no chain\n",
889 			(intmax_t)bref->data_off);
890 		goto done;
891 	}
892 	if (chain->error) {
893 		kprintf("hammer2_freemap_adjust: %016jx: error %s\n",
894 			(intmax_t)bref->data_off,
895 			hammer2_error_str(chain->error));
896 		hammer2_chain_unlock(chain);
897 		hammer2_chain_drop(chain);
898 		chain = NULL;
899 		goto done;
900 	}
901 
902 	/*
903 	 * Create any missing leaf(s) if we are doing a recovery (marking
904 	 * the block(s) as being allocated instead of being freed).  Be sure
905 	 * to initialize the auxillary freemap tracking info in the
906 	 * bref.check.freemap structure.
907 	 */
908 	if (chain == NULL && how == HAMMER2_FREEMAP_DORECOVER) {
909 		error = hammer2_chain_create(&parent, &chain,
910 				     hmp->spmp, HAMMER2_METH_DEFAULT,
911 				     key, HAMMER2_FREEMAP_LEVEL1_RADIX,
912 				     HAMMER2_BREF_TYPE_FREEMAP_LEAF,
913 				     HAMMER2_FREEMAP_LEVELN_PSIZE,
914 				     mtid, 0, 0);
915 
916 		if (hammer2_debug & 0x0040) {
917 			kprintf("fixup create chain %p %016jx:%d\n",
918 				chain, chain->bref.key, chain->bref.keybits);
919 		}
920 
921 		if (error == 0) {
922 			hammer2_chain_modify(chain, mtid, 0, 0);
923 			bzero(&chain->data->bmdata[0],
924 			      HAMMER2_FREEMAP_LEVELN_PSIZE);
925 			chain->bref.check.freemap.bigmask = (uint32_t)-1;
926 			chain->bref.check.freemap.avail = l1size;
927 			/* bref.methods should already be inherited */
928 
929 			hammer2_freemap_init(hmp, key, chain);
930 		}
931 		/* XXX handle error */
932 	}
933 
934 #if FREEMAP_DEBUG
935 	kprintf("FREEMAP ADJUST TYPE %d %016jx/%d DATA_OFF=%016jx\n",
936 		chain->bref.type, chain->bref.key,
937 		chain->bref.keybits, chain->bref.data_off);
938 #endif
939 
940 	/*
941 	 * Calculate the bitmask (runs in 2-bit pairs).
942 	 */
943 	start = ((int)(data_off >> HAMMER2_FREEMAP_BLOCK_RADIX) & 15) * 2;
944 	bmmask01 = (hammer2_bitmap_t)1 << start;
945 	bmmask10 = (hammer2_bitmap_t)2 << start;
946 	bmmask11 = (hammer2_bitmap_t)3 << start;
947 
948 	/*
949 	 * Fixup the bitmap.  Partial blocks cannot be fully freed unless
950 	 * a bulk scan is able to roll them up.
951 	 */
952 	if (radix < HAMMER2_FREEMAP_BLOCK_RADIX) {
953 		count = 1;
954 		if (how == HAMMER2_FREEMAP_DOREALFREE)
955 			how = HAMMER2_FREEMAP_DOMAYFREE;
956 	} else {
957 		count = 1 << (radix - HAMMER2_FREEMAP_BLOCK_RADIX);
958 	}
959 
960 	/*
961 	 * [re]load the bmap and bitmap pointers.  Each bmap entry covers
962 	 * a 2MB swath.  The bmap itself (LEVEL1) covers 2GB.
963 	 *
964 	 * Be sure to reset the linear iterator to ensure that the adjustment
965 	 * is not ignored.
966 	 */
967 again:
968 	bmap = &chain->data->bmdata[(int)(data_off >> HAMMER2_SEGRADIX) &
969 				    (HAMMER2_FREEMAP_COUNT - 1)];
970 	bitmap = &bmap->bitmapq[(int)(data_off >> (HAMMER2_SEGRADIX - 3)) & 7];
971 
972 	if (modified)
973 		bmap->linear = 0;
974 
975 	while (count) {
976 		KKASSERT(bmmask11);
977 		if (how == HAMMER2_FREEMAP_DORECOVER) {
978 			/*
979 			 * Recovery request, mark as allocated.
980 			 */
981 			if ((*bitmap & bmmask11) != bmmask11) {
982 				if (modified == 0) {
983 					hammer2_chain_modify(chain, mtid, 0, 0);
984 					modified = 1;
985 					goto again;
986 				}
987 				if ((*bitmap & bmmask11) == bmmask00) {
988 					bmap->avail -=
989 						HAMMER2_FREEMAP_BLOCK_SIZE;
990 					bgsize += HAMMER2_FREEMAP_BLOCK_SIZE;
991 				}
992 				if (bmap->class == 0)
993 					bmap->class = class;
994 				*bitmap |= bmmask11;
995 				if (hammer2_debug & 0x0040) {
996 					kprintf("hammer2_freemap_recover: "
997 						"fixup type=%02x "
998 						"block=%016jx/%zd\n",
999 						bref->type, data_off, bytes);
1000 				}
1001 			} else {
1002 				/*
1003 				kprintf("hammer2_freemap_recover:  good "
1004 					"type=%02x block=%016jx/%zd\n",
1005 					bref->type, data_off, bytes);
1006 				*/
1007 			}
1008 		}
1009 #if 0
1010 		/*
1011 		 * XXX this stuff doesn't work, avail is miscalculated and
1012 		 * code 10 means something else now.
1013 		 */
1014 		else if ((*bitmap & bmmask11) == bmmask11) {
1015 			/*
1016 			 * Mayfree/Realfree request and bitmap is currently
1017 			 * marked as being fully allocated.
1018 			 */
1019 			if (!modified) {
1020 				hammer2_chain_modify(chain, 0);
1021 				modified = 1;
1022 				goto again;
1023 			}
1024 			if (how == HAMMER2_FREEMAP_DOREALFREE)
1025 				*bitmap &= ~bmmask11;
1026 			else
1027 				*bitmap = (*bitmap & ~bmmask11) | bmmask10;
1028 		} else if ((*bitmap & bmmask11) == bmmask10) {
1029 			/*
1030 			 * Mayfree/Realfree request and bitmap is currently
1031 			 * marked as being possibly freeable.
1032 			 */
1033 			if (how == HAMMER2_FREEMAP_DOREALFREE) {
1034 				if (!modified) {
1035 					hammer2_chain_modify(chain, 0);
1036 					modified = 1;
1037 					goto again;
1038 				}
1039 				*bitmap &= ~bmmask11;
1040 			}
1041 		} else {
1042 			/*
1043 			 * 01 - Not implemented, currently illegal state
1044 			 * 00 - Not allocated at all, illegal free.
1045 			 */
1046 			panic("hammer2_freemap_adjust: "
1047 			      "Illegal state %08x(%08x)",
1048 			      *bitmap, *bitmap & bmmask11);
1049 		}
1050 #endif
1051 		--count;
1052 		bmmask01 <<= 2;
1053 		bmmask10 <<= 2;
1054 		bmmask11 <<= 2;
1055 	}
1056 #if HAMMER2_BMAP_ELEMENTS != 8
1057 #error "hammer2_freemap.c: HAMMER2_BMAP_ELEMENTS expected to be 8"
1058 #endif
1059 	if (how == HAMMER2_FREEMAP_DOREALFREE && modified) {
1060 		bmap->avail += 1 << radix;
1061 		KKASSERT(bmap->avail <= HAMMER2_SEGSIZE);
1062 		if (bmap->avail == HAMMER2_SEGSIZE &&
1063 		    bmap->bitmapq[0] == 0 &&
1064 		    bmap->bitmapq[1] == 0 &&
1065 		    bmap->bitmapq[2] == 0 &&
1066 		    bmap->bitmapq[3] == 0 &&
1067 		    bmap->bitmapq[4] == 0 &&
1068 		    bmap->bitmapq[5] == 0 &&
1069 		    bmap->bitmapq[6] == 0 &&
1070 		    bmap->bitmapq[7] == 0) {
1071 			key = H2FMBASE(data_off, HAMMER2_FREEMAP_LEVEL0_RADIX);
1072 			kprintf("Freeseg %016jx\n", (intmax_t)key);
1073 			bmap->class = 0;
1074 		}
1075 	}
1076 
1077 	/*
1078 	 * chain->bref.check.freemap.bigmask (XXX)
1079 	 *
1080 	 * Setting bigmask is a hint to the allocation code that there might
1081 	 * be something allocatable.  We also set this in recovery... it
1082 	 * doesn't hurt and we might want to use the hint for other validation
1083 	 * operations later on.
1084 	 */
1085 	if (modified)
1086 		chain->bref.check.freemap.bigmask |= 1 << radix;
1087 
1088 	hammer2_chain_unlock(chain);
1089 	hammer2_chain_drop(chain);
1090 done:
1091 	hammer2_chain_unlock(parent);
1092 	hammer2_chain_drop(parent);
1093 
1094 	if (bgsize) {
1095 		hammer2_voldata_lock(hmp);
1096 		hammer2_voldata_modify(hmp);
1097 		hmp->voldata.allocator_free -= bgsize;
1098 		hammer2_voldata_unlock(hmp);
1099 	}
1100 }
1101 
1102 /*
1103  * Validate the freemap, in three stages.
1104  *
1105  * stage-1	ALLOCATED     -> POSSIBLY FREE
1106  *		POSSIBLY FREE -> POSSIBLY FREE (type corrected)
1107  *
1108  *	This transitions bitmap entries from ALLOCATED to POSSIBLY FREE.
1109  *	The POSSIBLY FREE state does not mean that a block is actually free
1110  *	and may be transitioned back to ALLOCATED in stage-2.
1111  *
1112  *	This is typically done during normal filesystem operations when
1113  *	something is deleted or a block is replaced.
1114  *
1115  *	This is done by bulkfree in-bulk after a memory-bounded meta-data
1116  *	scan to try to determine what might be freeable.
1117  *
1118  *	This can be done unconditionally through a freemap scan when the
1119  *	intention is to brute-force recover the proper state of the freemap.
1120  *
1121  * stage-2	POSSIBLY FREE -> ALLOCATED	(scan metadata topology)
1122  *
1123  *	This is done by bulkfree during a meta-data scan to ensure that
1124  *	all blocks still actually allocated by the filesystem are marked
1125  *	as such.
1126  *
1127  *	NOTE! Live filesystem transitions to POSSIBLY FREE can occur while
1128  *	      the bulkfree stage-2 and stage-3 is running.  The live filesystem
1129  *	      will use the alternative POSSIBLY FREE type (2) to prevent
1130  *	      stage-3 from improperly transitioning unvetted possibly-free
1131  *	      blocks to FREE.
1132  *
1133  * stage-3	POSSIBLY FREE (type 1) -> FREE	(scan freemap)
1134  *
1135  *	This is done by bulkfree to finalize POSSIBLY FREE states.
1136  *
1137  */
1138