zfeature.c revision 288572
1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
24 */
25
26#include <sys/zfs_context.h>
27#include <sys/zfeature.h>
28#include <sys/dmu.h>
29#include <sys/nvpair.h>
30#include <sys/zap.h>
31#include <sys/dmu_tx.h>
32#include "zfeature_common.h"
33#include <sys/spa_impl.h>
34
35/*
36 * ZFS Feature Flags
37 * -----------------
38 *
39 * ZFS feature flags are used to provide fine-grained versioning to the ZFS
40 * on-disk format. Once enabled on a pool feature flags replace the old
41 * spa_version() number.
42 *
43 * Each new on-disk format change will be given a uniquely identifying string
44 * guid rather than a version number. This avoids the problem of different
45 * organizations creating new on-disk formats with the same version number. To
46 * keep feature guids unique they should consist of the reverse dns name of the
47 * organization which implemented the feature and a short name for the feature,
48 * separated by a colon (e.g. com.delphix:async_destroy).
49 *
50 * Reference Counts
51 * ----------------
52 *
53 * Within each pool features can be in one of three states: disabled, enabled,
54 * or active. These states are differentiated by a reference count stored on
55 * disk for each feature:
56 *
57 *   1) If there is no reference count stored on disk the feature is disabled.
58 *   2) If the reference count is 0 a system administrator has enabled the
59 *      feature, but the feature has not been used yet, so no on-disk
60 *      format changes have been made.
61 *   3) If the reference count is greater than 0 the feature is active.
62 *      The format changes required by the feature are currently on disk.
63 *      Note that if the feature's format changes are reversed the feature
64 *      may choose to set its reference count back to 0.
65 *
66 * Feature flags makes no differentiation between non-zero reference counts
67 * for an active feature (e.g. a reference count of 1 means the same thing as a
68 * reference count of 27834721), but feature implementations may choose to use
69 * the reference count to store meaningful information. For example, a new RAID
70 * implementation might set the reference count to the number of vdevs using
71 * it. If all those disks are removed from the pool the feature goes back to
72 * having a reference count of 0.
73 *
74 * It is the responsibility of the individual features to maintain a non-zero
75 * reference count as long as the feature's format changes are present on disk.
76 *
77 * Dependencies
78 * ------------
79 *
80 * Each feature may depend on other features. The only effect of this
81 * relationship is that when a feature is enabled all of its dependencies are
82 * automatically enabled as well. Any future work to support disabling of
83 * features would need to ensure that features cannot be disabled if other
84 * enabled features depend on them.
85 *
86 * On-disk Format
87 * --------------
88 *
89 * When feature flags are enabled spa_version() is set to SPA_VERSION_FEATURES
90 * (5000). In order for this to work the pool is automatically upgraded to
91 * SPA_VERSION_BEFORE_FEATURES (28) first, so all pre-feature flags on disk
92 * format changes will be in use.
93 *
94 * Information about features is stored in 3 ZAP objects in the pool's MOS.
95 * These objects are linked to by the following names in the pool directory
96 * object:
97 *
98 * 1) features_for_read: feature guid -> reference count
99 *    Features needed to open the pool for reading.
100 * 2) features_for_write: feature guid -> reference count
101 *    Features needed to open the pool for writing.
102 * 3) feature_descriptions: feature guid -> descriptive string
103 *    A human readable string.
104 *
105 * All enabled features appear in either features_for_read or
106 * features_for_write, but not both.
107 *
108 * To open a pool in read-only mode only the features listed in
109 * features_for_read need to be supported.
110 *
111 * To open the pool in read-write mode features in both features_for_read and
112 * features_for_write need to be supported.
113 *
114 * Some features may be required to read the ZAP objects containing feature
115 * information. To allow software to check for compatibility with these features
116 * before the pool is opened their names must be stored in the label in a
117 * new "features_for_read" entry (note that features that are only required
118 * to write to a pool never need to be stored in the label since the
119 * features_for_write ZAP object can be read before the pool is written to).
120 * To save space in the label features must be explicitly marked as needing to
121 * be written to the label. Also, reference counts are not stored in the label,
122 * instead any feature whose reference count drops to 0 is removed from the
123 * label.
124 *
125 * Adding New Features
126 * -------------------
127 *
128 * Features must be registered in zpool_feature_init() function in
129 * zfeature_common.c using the zfeature_register() function. This function
130 * has arguments to specify if the feature should be stored in the
131 * features_for_read or features_for_write ZAP object and if it needs to be
132 * written to the label when active.
133 *
134 * Once a feature is registered it will appear as a "feature@<feature name>"
135 * property which can be set by an administrator. Feature implementors should
136 * use the spa_feature_is_enabled() and spa_feature_is_active() functions to
137 * query the state of a feature and the spa_feature_incr() and
138 * spa_feature_decr() functions to change an enabled feature's reference count.
139 * Reference counts may only be updated in the syncing context.
140 *
141 * Features may not perform enable-time initialization. Instead, any such
142 * initialization should occur when the feature is first used. This design
143 * enforces that on-disk changes be made only when features are used. Code
144 * should only check if a feature is enabled using spa_feature_is_enabled(),
145 * not by relying on any feature specific metadata existing. If a feature is
146 * enabled, but the feature's metadata is not on disk yet then it should be
147 * created as needed.
148 *
149 * As an example, consider the com.delphix:async_destroy feature. This feature
150 * relies on the existence of a bptree in the MOS that store blocks for
151 * asynchronous freeing. This bptree is not created when async_destroy is
152 * enabled. Instead, when a dataset is destroyed spa_feature_is_enabled() is
153 * called to check if async_destroy is enabled. If it is and the bptree object
154 * does not exist yet, the bptree object is created as part of the dataset
155 * destroy and async_destroy's reference count is incremented to indicate it
156 * has made an on-disk format change. Later, after the destroyed dataset's
157 * blocks have all been asynchronously freed there is no longer any use for the
158 * bptree object, so it is destroyed and async_destroy's reference count is
159 * decremented back to 0 to indicate that it has undone its on-disk format
160 * changes.
161 */
162
163typedef enum {
164	FEATURE_ACTION_INCR,
165	FEATURE_ACTION_DECR,
166} feature_action_t;
167
168/*
169 * Checks that the active features in the pool are supported by
170 * this software.  Adds each unsupported feature (name -> description) to
171 * the supplied nvlist.
172 */
173boolean_t
174spa_features_check(spa_t *spa, boolean_t for_write,
175    nvlist_t *unsup_feat, nvlist_t *enabled_feat)
176{
177	objset_t *os = spa->spa_meta_objset;
178	boolean_t supported;
179	zap_cursor_t zc;
180	zap_attribute_t za;
181	uint64_t obj = for_write ?
182	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
183
184	supported = B_TRUE;
185	for (zap_cursor_init(&zc, os, obj);
186	    zap_cursor_retrieve(&zc, &za) == 0;
187	    zap_cursor_advance(&zc)) {
188		ASSERT(za.za_integer_length == sizeof (uint64_t) &&
189		    za.za_num_integers == 1);
190
191		if (NULL != enabled_feat) {
192			fnvlist_add_uint64(enabled_feat, za.za_name,
193			    za.za_first_integer);
194		}
195
196		if (za.za_first_integer != 0 &&
197		    !zfeature_is_supported(za.za_name)) {
198			supported = B_FALSE;
199
200			if (NULL != unsup_feat) {
201				char *desc = "";
202				char buf[MAXPATHLEN];
203
204				if (zap_lookup(os, spa->spa_feat_desc_obj,
205				    za.za_name, 1, sizeof (buf), buf) == 0)
206					desc = buf;
207
208				VERIFY(nvlist_add_string(unsup_feat, za.za_name,
209				    desc) == 0);
210			}
211		}
212	}
213	zap_cursor_fini(&zc);
214
215	return (supported);
216}
217
218/*
219 * Use an in-memory cache of feature refcounts for quick retrieval.
220 *
221 * Note: well-designed features will not need to use this; they should
222 * use spa_feature_is_enabled() and spa_feature_is_active() instead.
223 * However, this is non-static for zdb and zhack.
224 */
225int
226feature_get_refcount(spa_t *spa, zfeature_info_t *feature, uint64_t *res)
227{
228	ASSERT(VALID_FEATURE_FID(feature->fi_feature));
229	if (spa->spa_feat_refcount_cache[feature->fi_feature] ==
230	    SPA_FEATURE_DISABLED) {
231		return (SET_ERROR(ENOTSUP));
232	}
233	*res = spa->spa_feat_refcount_cache[feature->fi_feature];
234	return (0);
235}
236
237/*
238 * Note: well-designed features will not need to use this; they should
239 * use spa_feature_is_enabled() and spa_feature_is_active() instead.
240 * However, this is non-static for zdb and zhack.
241 */
242int
243feature_get_refcount_from_disk(spa_t *spa, zfeature_info_t *feature,
244    uint64_t *res)
245{
246	int err;
247	uint64_t refcount;
248	uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
249	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
250
251	/*
252	 * If the pool is currently being created, the feature objects may not
253	 * have been allocated yet.  Act as though all features are disabled.
254	 */
255	if (zapobj == 0)
256		return (SET_ERROR(ENOTSUP));
257
258	err = zap_lookup(spa->spa_meta_objset, zapobj,
259	    feature->fi_guid, sizeof (uint64_t), 1, &refcount);
260	if (err != 0) {
261		if (err == ENOENT)
262			return (SET_ERROR(ENOTSUP));
263		else
264			return (err);
265	}
266	*res = refcount;
267	return (0);
268}
269
270
271static int
272feature_get_enabled_txg(spa_t *spa, zfeature_info_t *feature, uint64_t *res) {
273	uint64_t enabled_txg_obj = spa->spa_feat_enabled_txg_obj;
274
275	ASSERT(zfeature_depends_on(feature->fi_feature,
276	    SPA_FEATURE_ENABLED_TXG));
277
278	if (!spa_feature_is_enabled(spa, feature->fi_feature)) {
279		return (SET_ERROR(ENOTSUP));
280	}
281
282	ASSERT(enabled_txg_obj != 0);
283
284	VERIFY0(zap_lookup(spa->spa_meta_objset, spa->spa_feat_enabled_txg_obj,
285	    feature->fi_guid, sizeof (uint64_t), 1, res));
286
287	return (0);
288}
289
290/*
291 * This function is non-static for zhack; it should otherwise not be used
292 * outside this file.
293 */
294void
295feature_sync(spa_t *spa, zfeature_info_t *feature, uint64_t refcount,
296    dmu_tx_t *tx)
297{
298	ASSERT(VALID_FEATURE_OR_NONE(feature->fi_feature));
299	uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
300	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
301
302	VERIFY0(zap_update(spa->spa_meta_objset, zapobj, feature->fi_guid,
303	    sizeof (uint64_t), 1, &refcount, tx));
304
305	/*
306	 * feature_sync is called directly from zhack, allowing the
307	 * creation of arbitrary features whose fi_feature field may
308	 * be greater than SPA_FEATURES. When called from zhack, the
309	 * zfeature_info_t object's fi_feature field will be set to
310	 * SPA_FEATURE_NONE.
311	 */
312	if (feature->fi_feature != SPA_FEATURE_NONE) {
313		uint64_t *refcount_cache =
314		    &spa->spa_feat_refcount_cache[feature->fi_feature];
315#ifdef atomic_swap_64
316		VERIFY3U(*refcount_cache, ==,
317		    atomic_swap_64(refcount_cache, refcount));
318#else
319		*refcount_cache = refcount;
320#endif
321	}
322
323	if (refcount == 0)
324		spa_deactivate_mos_feature(spa, feature->fi_guid);
325	else if (feature->fi_flags & ZFEATURE_FLAG_MOS)
326		spa_activate_mos_feature(spa, feature->fi_guid, tx);
327}
328
329/*
330 * This function is non-static for zhack; it should otherwise not be used
331 * outside this file.
332 */
333void
334feature_enable_sync(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
335{
336	uint64_t initial_refcount =
337	    (feature->fi_flags & ZFEATURE_FLAG_ACTIVATE_ON_ENABLE) ? 1 : 0;
338	uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
339	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
340
341	ASSERT(0 != zapobj);
342	ASSERT(zfeature_is_valid_guid(feature->fi_guid));
343	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
344
345	/*
346	 * If the feature is already enabled, ignore the request.
347	 */
348	if (zap_contains(spa->spa_meta_objset, zapobj, feature->fi_guid) == 0)
349		return;
350
351	for (int i = 0; feature->fi_depends[i] != SPA_FEATURE_NONE; i++)
352		spa_feature_enable(spa, feature->fi_depends[i], tx);
353
354	VERIFY0(zap_update(spa->spa_meta_objset, spa->spa_feat_desc_obj,
355	    feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
356	    feature->fi_desc, tx));
357
358	feature_sync(spa, feature, initial_refcount, tx);
359
360	if (spa_feature_is_enabled(spa, SPA_FEATURE_ENABLED_TXG)) {
361		uint64_t enabling_txg = dmu_tx_get_txg(tx);
362
363		if (spa->spa_feat_enabled_txg_obj == 0ULL) {
364			spa->spa_feat_enabled_txg_obj =
365			    zap_create_link(spa->spa_meta_objset,
366			    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
367			    DMU_POOL_FEATURE_ENABLED_TXG, tx);
368		}
369		spa_feature_incr(spa, SPA_FEATURE_ENABLED_TXG, tx);
370
371		VERIFY0(zap_add(spa->spa_meta_objset,
372		    spa->spa_feat_enabled_txg_obj, feature->fi_guid,
373		    sizeof (uint64_t), 1, &enabling_txg, tx));
374	}
375}
376
377static void
378feature_do_action(spa_t *spa, spa_feature_t fid, feature_action_t action,
379    dmu_tx_t *tx)
380{
381	uint64_t refcount;
382	zfeature_info_t *feature = &spa_feature_table[fid];
383	uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
384	    spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
385
386	ASSERT(VALID_FEATURE_FID(fid));
387	ASSERT(0 != zapobj);
388	ASSERT(zfeature_is_valid_guid(feature->fi_guid));
389
390	ASSERT(dmu_tx_is_syncing(tx));
391	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
392
393	VERIFY3U(feature_get_refcount(spa, feature, &refcount), !=, ENOTSUP);
394
395	switch (action) {
396	case FEATURE_ACTION_INCR:
397		VERIFY3U(refcount, !=, UINT64_MAX);
398		refcount++;
399		break;
400	case FEATURE_ACTION_DECR:
401		VERIFY3U(refcount, !=, 0);
402		refcount--;
403		break;
404	default:
405		ASSERT(0);
406		break;
407	}
408
409	feature_sync(spa, feature, refcount, tx);
410}
411
412void
413spa_feature_create_zap_objects(spa_t *spa, dmu_tx_t *tx)
414{
415	/*
416	 * We create feature flags ZAP objects in two instances: during pool
417	 * creation and during pool upgrade.
418	 */
419	ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)) || (!spa->spa_sync_on &&
420	    tx->tx_txg == TXG_INITIAL));
421
422	spa->spa_feat_for_read_obj = zap_create_link(spa->spa_meta_objset,
423	    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
424	    DMU_POOL_FEATURES_FOR_READ, tx);
425	spa->spa_feat_for_write_obj = zap_create_link(spa->spa_meta_objset,
426	    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
427	    DMU_POOL_FEATURES_FOR_WRITE, tx);
428	spa->spa_feat_desc_obj = zap_create_link(spa->spa_meta_objset,
429	    DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
430	    DMU_POOL_FEATURE_DESCRIPTIONS, tx);
431}
432
433/*
434 * Enable any required dependencies, then enable the requested feature.
435 */
436void
437spa_feature_enable(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
438{
439	ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
440	ASSERT(VALID_FEATURE_FID(fid));
441	feature_enable_sync(spa, &spa_feature_table[fid], tx);
442}
443
444void
445spa_feature_incr(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
446{
447	feature_do_action(spa, fid, FEATURE_ACTION_INCR, tx);
448}
449
450void
451spa_feature_decr(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
452{
453	feature_do_action(spa, fid, FEATURE_ACTION_DECR, tx);
454}
455
456boolean_t
457spa_feature_is_enabled(spa_t *spa, spa_feature_t fid)
458{
459	int err;
460	uint64_t refcount;
461
462	ASSERT(VALID_FEATURE_FID(fid));
463	if (spa_version(spa) < SPA_VERSION_FEATURES)
464		return (B_FALSE);
465
466	err = feature_get_refcount(spa, &spa_feature_table[fid], &refcount);
467	ASSERT(err == 0 || err == ENOTSUP);
468	return (err == 0);
469}
470
471boolean_t
472spa_feature_is_active(spa_t *spa, spa_feature_t fid)
473{
474	int err;
475	uint64_t refcount;
476
477	ASSERT(VALID_FEATURE_FID(fid));
478	if (spa_version(spa) < SPA_VERSION_FEATURES)
479		return (B_FALSE);
480
481	err = feature_get_refcount(spa, &spa_feature_table[fid], &refcount);
482	ASSERT(err == 0 || err == ENOTSUP);
483	return (err == 0 && refcount > 0);
484}
485
486/*
487 * For the feature specified by fid (which must depend on
488 * SPA_FEATURE_ENABLED_TXG), return the TXG at which it was enabled in the
489 * OUT txg argument.
490 *
491 * Returns B_TRUE if the feature is enabled, in which case txg will be filled
492 * with the transaction group in which the specified feature was enabled.
493 * Returns B_FALSE otherwise (i.e. if the feature is not enabled).
494 */
495boolean_t
496spa_feature_enabled_txg(spa_t *spa, spa_feature_t fid, uint64_t *txg) {
497	int err;
498
499	ASSERT(VALID_FEATURE_FID(fid));
500	if (spa_version(spa) < SPA_VERSION_FEATURES)
501		return (B_FALSE);
502
503	err = feature_get_enabled_txg(spa, &spa_feature_table[fid], txg);
504	ASSERT(err == 0 || err == ENOTSUP);
505
506	return (err == 0);
507}
508