summaryrefslogtreecommitdiff
path: root/fs/xfs/libxfs/xfs_ag.c
blob: 5de296b34ab1f618ea489225cbcd054bfd9aa7f9 (plain)
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
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * Copyright (c) 2018 Red Hat, Inc.
 * All rights reserved.
 */

#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_trans_resv.h"
#include "xfs_bit.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_rmap_btree.h"
#include "xfs_alloc.h"
#include "xfs_ialloc.h"
#include "xfs_rmap.h"
#include "xfs_ag.h"
#include "xfs_ag_resv.h"
#include "xfs_health.h"

static struct xfs_buf *
xfs_get_aghdr_buf(
	struct xfs_mount	*mp,
	xfs_daddr_t		blkno,
	size_t			numblks,
	int			flags,
	const struct xfs_buf_ops *ops)
{
	struct xfs_buf		*bp;

	bp = xfs_buf_get_uncached(mp->m_ddev_targp, numblks, flags);
	if (!bp)
		return NULL;

	xfs_buf_zero(bp, 0, BBTOB(bp->b_length));
	bp->b_bn = blkno;
	bp->b_maps[0].bm_bn = blkno;
	bp->b_ops = ops;

	return bp;
}

static inline bool is_log_ag(struct xfs_mount *mp, struct aghdr_init_data *id)
{
	return mp->m_sb.sb_logstart > 0 &&
	       id->agno == XFS_FSB_TO_AGNO(mp, mp->m_sb.sb_logstart);
}

/*
 * Generic btree root block init function
 */
static void
xfs_btroot_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	xfs_btree_init_block(mp, bp, id->type, 0, 0, id->agno);
}

/* Finish initializing a free space btree. */
static void
xfs_freesp_init_recs(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_alloc_rec	*arec;
	struct xfs_btree_block	*block = XFS_BUF_TO_BLOCK(bp);

	arec = XFS_ALLOC_REC_ADDR(mp, XFS_BUF_TO_BLOCK(bp), 1);
	arec->ar_startblock = cpu_to_be32(mp->m_ag_prealloc_blocks);

	if (is_log_ag(mp, id)) {
		struct xfs_alloc_rec	*nrec;
		xfs_agblock_t		start = XFS_FSB_TO_AGBNO(mp,
							mp->m_sb.sb_logstart);

		ASSERT(start >= mp->m_ag_prealloc_blocks);
		if (start != mp->m_ag_prealloc_blocks) {
			/*
			 * Modify first record to pad stripe align of log
			 */
			arec->ar_blockcount = cpu_to_be32(start -
						mp->m_ag_prealloc_blocks);
			nrec = arec + 1;

			/*
			 * Insert second record at start of internal log
			 * which then gets trimmed.
			 */
			nrec->ar_startblock = cpu_to_be32(
					be32_to_cpu(arec->ar_startblock) +
					be32_to_cpu(arec->ar_blockcount));
			arec = nrec;
			be16_add_cpu(&block->bb_numrecs, 1);
		}
		/*
		 * Change record start to after the internal log
		 */
		be32_add_cpu(&arec->ar_startblock, mp->m_sb.sb_logblocks);
	}

	/*
	 * Calculate the record block count and check for the case where
	 * the log might have consumed all available space in the AG. If
	 * so, reset the record count to 0 to avoid exposure of an invalid
	 * record start block.
	 */
	arec->ar_blockcount = cpu_to_be32(id->agsize -
					  be32_to_cpu(arec->ar_startblock));
	if (!arec->ar_blockcount)
		block->bb_numrecs = 0;
}

/*
 * Alloc btree root block init functions
 */
static void
xfs_bnoroot_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	xfs_btree_init_block(mp, bp, XFS_BTNUM_BNO, 0, 1, id->agno);
	xfs_freesp_init_recs(mp, bp, id);
}

static void
xfs_cntroot_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	xfs_btree_init_block(mp, bp, XFS_BTNUM_CNT, 0, 1, id->agno);
	xfs_freesp_init_recs(mp, bp, id);
}

/*
 * Reverse map root block init
 */
static void
xfs_rmaproot_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_btree_block	*block = XFS_BUF_TO_BLOCK(bp);
	struct xfs_rmap_rec	*rrec;

	xfs_btree_init_block(mp, bp, XFS_BTNUM_RMAP, 0, 4, id->agno);

	/*
	 * mark the AG header regions as static metadata The BNO
	 * btree block is the first block after the headers, so
	 * it's location defines the size of region the static
	 * metadata consumes.
	 *
	 * Note: unlike mkfs, we never have to account for log
	 * space when growing the data regions
	 */
	rrec = XFS_RMAP_REC_ADDR(block, 1);
	rrec->rm_startblock = 0;
	rrec->rm_blockcount = cpu_to_be32(XFS_BNO_BLOCK(mp));
	rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_FS);
	rrec->rm_offset = 0;

	/* account freespace btree root blocks */
	rrec = XFS_RMAP_REC_ADDR(block, 2);
	rrec->rm_startblock = cpu_to_be32(XFS_BNO_BLOCK(mp));
	rrec->rm_blockcount = cpu_to_be32(2);
	rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_AG);
	rrec->rm_offset = 0;

	/* account inode btree root blocks */
	rrec = XFS_RMAP_REC_ADDR(block, 3);
	rrec->rm_startblock = cpu_to_be32(XFS_IBT_BLOCK(mp));
	rrec->rm_blockcount = cpu_to_be32(XFS_RMAP_BLOCK(mp) -
					  XFS_IBT_BLOCK(mp));
	rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_INOBT);
	rrec->rm_offset = 0;

	/* account for rmap btree root */
	rrec = XFS_RMAP_REC_ADDR(block, 4);
	rrec->rm_startblock = cpu_to_be32(XFS_RMAP_BLOCK(mp));
	rrec->rm_blockcount = cpu_to_be32(1);
	rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_AG);
	rrec->rm_offset = 0;

	/* account for refc btree root */
	if (xfs_sb_version_hasreflink(&mp->m_sb)) {
		rrec = XFS_RMAP_REC_ADDR(block, 5);
		rrec->rm_startblock = cpu_to_be32(xfs_refc_block(mp));
		rrec->rm_blockcount = cpu_to_be32(1);
		rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_REFC);
		rrec->rm_offset = 0;
		be16_add_cpu(&block->bb_numrecs, 1);
	}

	/* account for the log space */
	if (is_log_ag(mp, id)) {
		rrec = XFS_RMAP_REC_ADDR(block,
				be16_to_cpu(block->bb_numrecs) + 1);
		rrec->rm_startblock = cpu_to_be32(
				XFS_FSB_TO_AGBNO(mp, mp->m_sb.sb_logstart));
		rrec->rm_blockcount = cpu_to_be32(mp->m_sb.sb_logblocks);
		rrec->rm_owner = cpu_to_be64(XFS_RMAP_OWN_LOG);
		rrec->rm_offset = 0;
		be16_add_cpu(&block->bb_numrecs, 1);
	}
}

/*
 * Initialise new secondary superblocks with the pre-grow geometry, but mark
 * them as "in progress" so we know they haven't yet been activated. This will
 * get cleared when the update with the new geometry information is done after
 * changes to the primary are committed. This isn't strictly necessary, but we
 * get it for free with the delayed buffer write lists and it means we can tell
 * if a grow operation didn't complete properly after the fact.
 */
static void
xfs_sbblock_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_dsb		*dsb = XFS_BUF_TO_SBP(bp);

	xfs_sb_to_disk(dsb, &mp->m_sb);
	dsb->sb_inprogress = 1;
}

static void
xfs_agfblock_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_agf		*agf = XFS_BUF_TO_AGF(bp);
	xfs_extlen_t		tmpsize;

	agf->agf_magicnum = cpu_to_be32(XFS_AGF_MAGIC);
	agf->agf_versionnum = cpu_to_be32(XFS_AGF_VERSION);
	agf->agf_seqno = cpu_to_be32(id->agno);
	agf->agf_length = cpu_to_be32(id->agsize);
	agf->agf_roots[XFS_BTNUM_BNOi] = cpu_to_be32(XFS_BNO_BLOCK(mp));
	agf->agf_roots[XFS_BTNUM_CNTi] = cpu_to_be32(XFS_CNT_BLOCK(mp));
	agf->agf_levels[XFS_BTNUM_BNOi] = cpu_to_be32(1);
	agf->agf_levels[XFS_BTNUM_CNTi] = cpu_to_be32(1);
	if (xfs_sb_version_hasrmapbt(&mp->m_sb)) {
		agf->agf_roots[XFS_BTNUM_RMAPi] =
					cpu_to_be32(XFS_RMAP_BLOCK(mp));
		agf->agf_levels[XFS_BTNUM_RMAPi] = cpu_to_be32(1);
		agf->agf_rmap_blocks = cpu_to_be32(1);
	}

	agf->agf_flfirst = cpu_to_be32(1);
	agf->agf_fllast = 0;
	agf->agf_flcount = 0;
	tmpsize = id->agsize - mp->m_ag_prealloc_blocks;
	agf->agf_freeblks = cpu_to_be32(tmpsize);
	agf->agf_longest = cpu_to_be32(tmpsize);
	if (xfs_sb_version_hascrc(&mp->m_sb))
		uuid_copy(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid);
	if (xfs_sb_version_hasreflink(&mp->m_sb)) {
		agf->agf_refcount_root = cpu_to_be32(
				xfs_refc_block(mp));
		agf->agf_refcount_level = cpu_to_be32(1);
		agf->agf_refcount_blocks = cpu_to_be32(1);
	}

	if (is_log_ag(mp, id)) {
		int64_t	logblocks = mp->m_sb.sb_logblocks;

		be32_add_cpu(&agf->agf_freeblks, -logblocks);
		agf->agf_longest = cpu_to_be32(id->agsize -
			XFS_FSB_TO_AGBNO(mp, mp->m_sb.sb_logstart) - logblocks);
	}
}

static void
xfs_agflblock_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_agfl		*agfl = XFS_BUF_TO_AGFL(bp);
	__be32			*agfl_bno;
	int			bucket;

	if (xfs_sb_version_hascrc(&mp->m_sb)) {
		agfl->agfl_magicnum = cpu_to_be32(XFS_AGFL_MAGIC);
		agfl->agfl_seqno = cpu_to_be32(id->agno);
		uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid);
	}

	agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, bp);
	for (bucket = 0; bucket < xfs_agfl_size(mp); bucket++)
		agfl_bno[bucket] = cpu_to_be32(NULLAGBLOCK);
}

static void
xfs_agiblock_init(
	struct xfs_mount	*mp,
	struct xfs_buf		*bp,
	struct aghdr_init_data	*id)
{
	struct xfs_agi		*agi = XFS_BUF_TO_AGI(bp);
	int			bucket;

	agi->agi_magicnum = cpu_to_be32(XFS_AGI_MAGIC);
	agi->agi_versionnum = cpu_to_be32(XFS_AGI_VERSION);
	agi->agi_seqno = cpu_to_be32(id->agno);
	agi->agi_length = cpu_to_be32(id->agsize);
	agi->agi_count = 0;
	agi->agi_root = cpu_to_be32(XFS_IBT_BLOCK(mp));
	agi->agi_level = cpu_to_be32(1);
	agi->agi_freecount = 0;
	agi->agi_newino = cpu_to_be32(NULLAGINO);
	agi->agi_dirino = cpu_to_be32(NULLAGINO);
	if (xfs_sb_version_hascrc(&mp->m_sb))
		uuid_copy(&agi->agi_uuid, &mp->m_sb.sb_meta_uuid);
	if (xfs_sb_version_hasfinobt(&mp->m_sb)) {
		agi->agi_free_root = cpu_to_be32(XFS_FIBT_BLOCK(mp));
		agi->agi_free_level = cpu_to_be32(1);
	}
	for (bucket = 0; bucket < XFS_AGI_UNLINKED_BUCKETS; bucket++)
		agi->agi_unlinked[bucket] = cpu_to_be32(NULLAGINO);
}

typedef void (*aghdr_init_work_f)(struct xfs_mount *mp, struct xfs_buf *bp,
				  struct aghdr_init_data *id);
static int
xfs_ag_init_hdr(
	struct xfs_mount	*mp,
	struct aghdr_init_data	*id,
	aghdr_init_work_f	work,
	const struct xfs_buf_ops *ops)

{
	struct xfs_buf		*bp;

	bp = xfs_get_aghdr_buf(mp, id->daddr, id->numblks, 0, ops);
	if (!bp)
		return -ENOMEM;

	(*work)(mp, bp, id);

	xfs_buf_delwri_queue(bp, &id->buffer_list);
	xfs_buf_relse(bp);
	return 0;
}

struct xfs_aghdr_grow_data {
	xfs_daddr_t		daddr;
	size_t			numblks;
	const struct xfs_buf_ops *ops;
	aghdr_init_work_f	work;
	xfs_btnum_t		type;
	bool			need_init;
};

/*
 * Prepare new AG headers to be written to disk. We use uncached buffers here,
 * as it is assumed these new AG headers are currently beyond the currently
 * valid filesystem address space. Using cached buffers would trip over EOFS
 * corruption detection alogrithms in the buffer cache lookup routines.
 *
 * This is a non-transactional function, but the prepared buffers are added to a
 * delayed write buffer list supplied by the caller so they can submit them to
 * disk and wait on them as required.
 */
int
xfs_ag_init_headers(
	struct xfs_mount	*mp,
	struct aghdr_init_data	*id)

{
	struct xfs_aghdr_grow_data aghdr_data[] = {
	{ /* SB */
		.daddr = XFS_AG_DADDR(mp, id->agno, XFS_SB_DADDR),
		.numblks = XFS_FSS_TO_BB(mp, 1),
		.ops = &xfs_sb_buf_ops,
		.work = &xfs_sbblock_init,
		.need_init = true
	},
	{ /* AGF */
		.daddr = XFS_AG_DADDR(mp, id->agno, XFS_AGF_DADDR(mp)),
		.numblks = XFS_FSS_TO_BB(mp, 1),
		.ops = &xfs_agf_buf_ops,
		.work = &xfs_agfblock_init,
		.need_init = true
	},
	{ /* AGFL */
		.daddr = XFS_AG_DADDR(mp, id->agno, XFS_AGFL_DADDR(mp)),
		.numblks = XFS_FSS_TO_BB(mp, 1),
		.ops = &xfs_agfl_buf_ops,
		.work = &xfs_agflblock_init,
		.need_init = true
	},
	{ /* AGI */
		.daddr = XFS_AG_DADDR(mp, id->agno, XFS_AGI_DADDR(mp)),
		.numblks = XFS_FSS_TO_BB(mp, 1),
		.ops = &xfs_agi_buf_ops,
		.work = &xfs_agiblock_init,
		.need_init = true
	},
	{ /* BNO root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, XFS_BNO_BLOCK(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_bnobt_buf_ops,
		.work = &xfs_bnoroot_init,
		.need_init = true
	},
	{ /* CNT root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, XFS_CNT_BLOCK(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_cntbt_buf_ops,
		.work = &xfs_cntroot_init,
		.need_init = true
	},
	{ /* INO root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, XFS_IBT_BLOCK(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_inobt_buf_ops,
		.work = &xfs_btroot_init,
		.type = XFS_BTNUM_INO,
		.need_init = true
	},
	{ /* FINO root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, XFS_FIBT_BLOCK(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_finobt_buf_ops,
		.work = &xfs_btroot_init,
		.type = XFS_BTNUM_FINO,
		.need_init =  xfs_sb_version_hasfinobt(&mp->m_sb)
	},
	{ /* RMAP root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, XFS_RMAP_BLOCK(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_rmapbt_buf_ops,
		.work = &xfs_rmaproot_init,
		.need_init = xfs_sb_version_hasrmapbt(&mp->m_sb)
	},
	{ /* REFC root block */
		.daddr = XFS_AGB_TO_DADDR(mp, id->agno, xfs_refc_block(mp)),
		.numblks = BTOBB(mp->m_sb.sb_blocksize),
		.ops = &xfs_refcountbt_buf_ops,
		.work = &xfs_btroot_init,
		.type = XFS_BTNUM_REFC,
		.need_init = xfs_sb_version_hasreflink(&mp->m_sb)
	},
	{ /* NULL terminating block */
		.daddr = XFS_BUF_DADDR_NULL,
	}
	};
	struct  xfs_aghdr_grow_data *dp;
	int			error = 0;

	/* Account for AG free space in new AG */
	id->nfree += id->agsize - mp->m_ag_prealloc_blocks;
	for (dp = &aghdr_data[0]; dp->daddr != XFS_BUF_DADDR_NULL; dp++) {
		if (!dp->need_init)
			continue;

		id->daddr = dp->daddr;
		id->numblks = dp->numblks;
		id->type = dp->type;
		error = xfs_ag_init_hdr(mp, id, dp->work, dp->ops);
		if (error)
			break;
	}
	return error;
}

/*
 * Extent the AG indicated by the @id by the length passed in
 */
int
xfs_ag_extend_space(
	struct xfs_mount	*mp,
	struct xfs_trans	*tp,
	struct aghdr_init_data	*id,
	xfs_extlen_t		len)
{
	struct xfs_buf		*bp;
	struct xfs_agi		*agi;
	struct xfs_agf		*agf;
	int			error;

	/*
	 * Change the agi length.
	 */
	error = xfs_ialloc_read_agi(mp, tp, id->agno, &bp);
	if (error)
		return error;

	agi = XFS_BUF_TO_AGI(bp);
	be32_add_cpu(&agi->agi_length, len);
	ASSERT(id->agno == mp->m_sb.sb_agcount - 1 ||
	       be32_to_cpu(agi->agi_length) == mp->m_sb.sb_agblocks);
	xfs_ialloc_log_agi(tp, bp, XFS_AGI_LENGTH);

	/*
	 * Change agf length.
	 */
	error = xfs_alloc_read_agf(mp, tp, id->agno, 0, &bp);
	if (error)
		return error;

	agf = XFS_BUF_TO_AGF(bp);
	be32_add_cpu(&agf->agf_length, len);
	ASSERT(agf->agf_length == agi->agi_length);
	xfs_alloc_log_agf(tp, bp, XFS_AGF_LENGTH);

	/*
	 * Free the new space.
	 *
	 * XFS_RMAP_OINFO_SKIP_UPDATE is used here to tell the rmap btree that
	 * this doesn't actually exist in the rmap btree.
	 */
	error = xfs_rmap_free(tp, bp, id->agno,
				be32_to_cpu(agf->agf_length) - len,
				len, &XFS_RMAP_OINFO_SKIP_UPDATE);
	if (error)
		return error;

	return  xfs_free_extent(tp, XFS_AGB_TO_FSB(mp, id->agno,
					be32_to_cpu(agf->agf_length) - len),
				len, &XFS_RMAP_OINFO_SKIP_UPDATE,
				XFS_AG_RESV_NONE);
}

/* Retrieve AG geometry. */
int
xfs_ag_get_geometry(
	struct xfs_mount	*mp,
	xfs_agnumber_t		agno,
	struct xfs_ag_geometry	*ageo)
{
	struct xfs_buf		*agi_bp;
	struct xfs_buf		*agf_bp;
	struct xfs_agi		*agi;
	struct xfs_agf		*agf;
	struct xfs_perag	*pag;
	unsigned int		freeblks;
	int			error;

	if (agno >= mp->m_sb.sb_agcount)
		return -EINVAL;

	/* Lock the AG headers. */
	error = xfs_ialloc_read_agi(mp, NULL, agno, &agi_bp);
	if (error)
		return error;
	error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agf_bp);
	if (error)
		goto out_agi;
	pag = xfs_perag_get(mp, agno);

	/* Fill out form. */
	memset(ageo, 0, sizeof(*ageo));
	ageo->ag_number = agno;

	agi = XFS_BUF_TO_AGI(agi_bp);
	ageo->ag_icount = be32_to_cpu(agi->agi_count);
	ageo->ag_ifree = be32_to_cpu(agi->agi_freecount);

	agf = XFS_BUF_TO_AGF(agf_bp);
	ageo->ag_length = be32_to_cpu(agf->agf_length);
	freeblks = pag->pagf_freeblks +
		   pag->pagf_flcount +
		   pag->pagf_btreeblks -
		   xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE);
	ageo->ag_freeblks = freeblks;
	xfs_ag_geom_health(pag, ageo);

	/* Release resources. */
	xfs_perag_put(pag);
	xfs_buf_relse(agf_bp);
out_agi:
	xfs_buf_relse(agi_bp);
	return error;
}