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.
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.
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]
23 * Copyright (c) 2012 by Delphix. All rights reserved.
26 #include <sys/zfs_context.h>
27 #include <sys/zfeature.h>
29 #include <sys/nvpair.h>
31 #include <sys/dmu_tx.h>
32 #include "zfeature_common.h"
33 #include <sys/spa_impl.h>
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.
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).
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:
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.
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.
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.
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.
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.
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
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.
105 * All enabled features appear in either features_for_read or
106 * features_for_write, but not both.
108 * To open a pool in read-only mode only the features listed in
109 * features_for_read need to be supported.
111 * To open the pool in read-write mode features in both features_for_read and
112 * features_for_write need to be supported.
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
125 * Adding New Features
126 * -------------------
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.
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.
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
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
164 FEATURE_ACTION_ENABLE,
170 * Checks that the features active in the specified object are supported by
171 * this software. Adds each unsupported feature (name -> description) to
172 * the supplied nvlist.
175 feature_is_supported(objset_t *os, uint64_t obj, uint64_t desc_obj,
176 nvlist_t *unsup_feat, nvlist_t *enabled_feat)
183 zc = kmem_alloc(sizeof(zap_cursor_t), KM_SLEEP);
184 za = kmem_alloc(sizeof(zap_attribute_t), KM_SLEEP);
185 buf = kmem_alloc(MAXPATHLEN, KM_SLEEP);
188 for (zap_cursor_init(zc, os, obj);
189 zap_cursor_retrieve(zc, za) == 0;
190 zap_cursor_advance(zc)) {
191 ASSERT(za->za_integer_length == sizeof (uint64_t) &&
192 za->za_num_integers == 1);
194 if (NULL != enabled_feat) {
195 fnvlist_add_uint64(enabled_feat, za->za_name,
196 za->za_first_integer);
199 if (za->za_first_integer != 0 &&
200 !zfeature_is_supported(za->za_name)) {
203 if (NULL != unsup_feat) {
206 if (zap_lookup(os, desc_obj, za->za_name,
207 1, sizeof (buf), buf) == 0)
210 VERIFY(nvlist_add_string(unsup_feat,
211 za->za_name, desc) == 0);
217 kmem_free(buf, MAXPATHLEN);
218 kmem_free(za, sizeof(zap_attribute_t));
219 kmem_free(zc, sizeof(zap_cursor_t));
225 feature_get_refcount(objset_t *os, uint64_t read_obj, uint64_t write_obj,
226 zfeature_info_t *feature, uint64_t *res)
230 uint64_t zapobj = feature->fi_can_readonly ? write_obj : read_obj;
234 err = zap_lookup(os, zapobj, feature->fi_guid, sizeof (uint64_t), 1,
247 feature_do_action(objset_t *os, uint64_t read_obj, uint64_t write_obj,
248 uint64_t desc_obj, zfeature_info_t *feature, feature_action_t action,
253 uint64_t zapobj = feature->fi_can_readonly ? write_obj : read_obj;
256 ASSERT(zfeature_is_valid_guid(feature->fi_guid));
258 error = zap_lookup(os, zapobj, feature->fi_guid,
259 sizeof (uint64_t), 1, &refcount);
262 * If we can't ascertain the status of the specified feature, an I/O
265 if (error != 0 && error != ENOENT)
269 case FEATURE_ACTION_ENABLE:
271 * If the feature is already enabled, ignore the request.
277 case FEATURE_ACTION_INCR:
280 if (refcount == UINT64_MAX)
284 case FEATURE_ACTION_DECR:
296 if (action == FEATURE_ACTION_ENABLE) {
299 for (i = 0; feature->fi_depends[i] != NULL; i++) {
300 zfeature_info_t *dep = feature->fi_depends[i];
302 error = feature_do_action(os, read_obj, write_obj,
303 desc_obj, dep, FEATURE_ACTION_ENABLE, tx);
309 error = zap_update(os, zapobj, feature->fi_guid,
310 sizeof (uint64_t), 1, &refcount, tx);
314 if (action == FEATURE_ACTION_ENABLE) {
315 error = zap_update(os, desc_obj,
316 feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
317 feature->fi_desc, tx);
322 if (action == FEATURE_ACTION_INCR && refcount == 1 && feature->fi_mos) {
323 spa_activate_mos_feature(dmu_objset_spa(os), feature->fi_guid);
326 if (action == FEATURE_ACTION_DECR && refcount == 0) {
327 spa_deactivate_mos_feature(dmu_objset_spa(os),
335 spa_feature_create_zap_objects(spa_t *spa, dmu_tx_t *tx)
338 * We create feature flags ZAP objects in two instances: during pool
339 * creation and during pool upgrade.
341 ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)) || (!spa->spa_sync_on &&
342 tx->tx_txg == TXG_INITIAL));
344 spa->spa_feat_for_read_obj = zap_create_link(spa->spa_meta_objset,
345 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
346 DMU_POOL_FEATURES_FOR_READ, tx);
347 spa->spa_feat_for_write_obj = zap_create_link(spa->spa_meta_objset,
348 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
349 DMU_POOL_FEATURES_FOR_WRITE, tx);
350 spa->spa_feat_desc_obj = zap_create_link(spa->spa_meta_objset,
351 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
352 DMU_POOL_FEATURE_DESCRIPTIONS, tx);
356 * Enable any required dependencies, then enable the requested feature.
359 spa_feature_enable(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
361 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
362 VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
363 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
364 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_ENABLE, tx));
368 * If the specified feature has not yet been enabled, this function returns
369 * ENOTSUP; otherwise, this function increments the feature's refcount (or
370 * returns EOVERFLOW if the refcount cannot be incremented). This function must
371 * be called from syncing context.
374 spa_feature_incr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
376 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
377 VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
378 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
379 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_INCR, tx));
383 * If the specified feature has not yet been enabled, this function returns
384 * ENOTSUP; otherwise, this function decrements the feature's refcount (or
385 * returns EOVERFLOW if the refcount is already 0). This function must
386 * be called from syncing context.
389 spa_feature_decr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
391 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
392 VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
393 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
394 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_DECR, tx));
398 spa_feature_is_enabled(spa_t *spa, zfeature_info_t *feature)
401 uint64_t refcount = 0;
403 if (spa_version(spa) < SPA_VERSION_FEATURES)
406 err = feature_get_refcount(spa->spa_meta_objset,
407 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
409 ASSERT(err == 0 || err == ENOTSUP);
414 spa_feature_is_active(spa_t *spa, zfeature_info_t *feature)
417 uint64_t refcount = 0;
419 if (spa_version(spa) < SPA_VERSION_FEATURES)
422 err = feature_get_refcount(spa->spa_meta_objset,
423 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
425 ASSERT(err == 0 || err == ENOTSUP);
426 return (err == 0 && refcount > 0);