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) 2013 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
;
233 * If the pool is currently being created, the feature objects may not
234 * have been allocated yet. Act as though all features are disabled.
237 return (SET_ERROR(ENOTSUP
));
239 err
= zap_lookup(os
, zapobj
, feature
->fi_guid
, sizeof (uint64_t), 1,
243 return (SET_ERROR(ENOTSUP
));
252 feature_do_action(objset_t
*os
, uint64_t read_obj
, uint64_t write_obj
,
253 uint64_t desc_obj
, zfeature_info_t
*feature
, feature_action_t action
,
258 uint64_t zapobj
= feature
->fi_can_readonly
? write_obj
: read_obj
;
261 ASSERT(zfeature_is_valid_guid(feature
->fi_guid
));
263 error
= zap_lookup(os
, zapobj
, feature
->fi_guid
,
264 sizeof (uint64_t), 1, &refcount
);
267 * If we can't ascertain the status of the specified feature, an I/O
270 if (error
!= 0 && error
!= ENOENT
)
274 case FEATURE_ACTION_ENABLE
:
276 * If the feature is already enabled, ignore the request.
282 case FEATURE_ACTION_INCR
:
284 return (SET_ERROR(ENOTSUP
));
285 if (refcount
== UINT64_MAX
)
286 return (SET_ERROR(EOVERFLOW
));
289 case FEATURE_ACTION_DECR
:
291 return (SET_ERROR(ENOTSUP
));
293 return (SET_ERROR(EOVERFLOW
));
301 if (action
== FEATURE_ACTION_ENABLE
) {
304 for (i
= 0; feature
->fi_depends
[i
] != NULL
; i
++) {
305 zfeature_info_t
*dep
= feature
->fi_depends
[i
];
307 error
= feature_do_action(os
, read_obj
, write_obj
,
308 desc_obj
, dep
, FEATURE_ACTION_ENABLE
, tx
);
314 error
= zap_update(os
, zapobj
, feature
->fi_guid
,
315 sizeof (uint64_t), 1, &refcount
, tx
);
319 if (action
== FEATURE_ACTION_ENABLE
) {
320 error
= zap_update(os
, desc_obj
,
321 feature
->fi_guid
, 1, strlen(feature
->fi_desc
) + 1,
322 feature
->fi_desc
, tx
);
327 if (action
== FEATURE_ACTION_INCR
&& refcount
== 1 && feature
->fi_mos
) {
328 spa_activate_mos_feature(dmu_objset_spa(os
), feature
->fi_guid
);
331 if (action
== FEATURE_ACTION_DECR
&& refcount
== 0) {
332 spa_deactivate_mos_feature(dmu_objset_spa(os
),
340 spa_feature_create_zap_objects(spa_t
*spa
, dmu_tx_t
*tx
)
343 * We create feature flags ZAP objects in two instances: during pool
344 * creation and during pool upgrade.
346 ASSERT(dsl_pool_sync_context(spa_get_dsl(spa
)) || (!spa
->spa_sync_on
&&
347 tx
->tx_txg
== TXG_INITIAL
));
349 spa
->spa_feat_for_read_obj
= zap_create_link(spa
->spa_meta_objset
,
350 DMU_OTN_ZAP_METADATA
, DMU_POOL_DIRECTORY_OBJECT
,
351 DMU_POOL_FEATURES_FOR_READ
, tx
);
352 spa
->spa_feat_for_write_obj
= zap_create_link(spa
->spa_meta_objset
,
353 DMU_OTN_ZAP_METADATA
, DMU_POOL_DIRECTORY_OBJECT
,
354 DMU_POOL_FEATURES_FOR_WRITE
, tx
);
355 spa
->spa_feat_desc_obj
= zap_create_link(spa
->spa_meta_objset
,
356 DMU_OTN_ZAP_METADATA
, DMU_POOL_DIRECTORY_OBJECT
,
357 DMU_POOL_FEATURE_DESCRIPTIONS
, tx
);
361 * Enable any required dependencies, then enable the requested feature.
364 spa_feature_enable(spa_t
*spa
, zfeature_info_t
*feature
, dmu_tx_t
*tx
)
366 ASSERT3U(spa_version(spa
), >=, SPA_VERSION_FEATURES
);
367 VERIFY3U(0, ==, feature_do_action(spa
->spa_meta_objset
,
368 spa
->spa_feat_for_read_obj
, spa
->spa_feat_for_write_obj
,
369 spa
->spa_feat_desc_obj
, feature
, FEATURE_ACTION_ENABLE
, tx
));
373 * If the specified feature has not yet been enabled, this function returns
374 * ENOTSUP; otherwise, this function increments the feature's refcount (or
375 * returns EOVERFLOW if the refcount cannot be incremented). This function must
376 * be called from syncing context.
379 spa_feature_incr(spa_t
*spa
, zfeature_info_t
*feature
, dmu_tx_t
*tx
)
381 ASSERT3U(spa_version(spa
), >=, SPA_VERSION_FEATURES
);
382 VERIFY3U(0, ==, feature_do_action(spa
->spa_meta_objset
,
383 spa
->spa_feat_for_read_obj
, spa
->spa_feat_for_write_obj
,
384 spa
->spa_feat_desc_obj
, feature
, FEATURE_ACTION_INCR
, tx
));
388 * If the specified feature has not yet been enabled, this function returns
389 * ENOTSUP; otherwise, this function decrements the feature's refcount (or
390 * returns EOVERFLOW if the refcount is already 0). This function must
391 * be called from syncing context.
394 spa_feature_decr(spa_t
*spa
, zfeature_info_t
*feature
, dmu_tx_t
*tx
)
396 ASSERT3U(spa_version(spa
), >=, SPA_VERSION_FEATURES
);
397 VERIFY3U(0, ==, feature_do_action(spa
->spa_meta_objset
,
398 spa
->spa_feat_for_read_obj
, spa
->spa_feat_for_write_obj
,
399 spa
->spa_feat_desc_obj
, feature
, FEATURE_ACTION_DECR
, tx
));
403 spa_feature_is_enabled(spa_t
*spa
, zfeature_info_t
*feature
)
406 uint64_t refcount
= 0;
408 if (spa_version(spa
) < SPA_VERSION_FEATURES
)
411 err
= feature_get_refcount(spa
->spa_meta_objset
,
412 spa
->spa_feat_for_read_obj
, spa
->spa_feat_for_write_obj
,
414 ASSERT(err
== 0 || err
== ENOTSUP
);
419 spa_feature_is_active(spa_t
*spa
, zfeature_info_t
*feature
)
422 uint64_t refcount
= 0;
424 if (spa_version(spa
) < SPA_VERSION_FEATURES
)
427 err
= feature_get_refcount(spa
->spa_meta_objset
,
428 spa
->spa_feat_for_read_obj
, spa
->spa_feat_for_write_obj
,
430 ASSERT(err
== 0 || err
== ENOTSUP
);
431 return (err
== 0 && refcount
> 0);