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) 2012 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
163 typedef enum {
164 FEATURE_ACTION_ENABLE,
165 FEATURE_ACTION_INCR,
166 FEATURE_ACTION_DECR,
167 } feature_action_t;
168
169 /*
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.
173 */
174 boolean_t
175 feature_is_supported(objset_t *os, uint64_t obj, uint64_t desc_obj,
176 nvlist_t *unsup_feat)
177 {
178 boolean_t supported;
179 zap_cursor_t zc;
180 zap_attribute_t za;
181
182 supported = B_TRUE;
183 for (zap_cursor_init(&zc, os, obj);
184 zap_cursor_retrieve(&zc, &za) == 0;
185 zap_cursor_advance(&zc)) {
186 ASSERT(za.za_integer_length == sizeof (uint64_t) &&
187 za.za_num_integers == 1);
188
189 if (za.za_first_integer != 0 &&
190 !zfeature_is_supported(za.za_name)) {
191 supported = B_FALSE;
192
193 if (unsup_feat != NULL) {
194 char *desc = "";
195 char buf[MAXPATHLEN];
196
197 if (zap_lookup(os, desc_obj, za.za_name,
198 1, sizeof (buf), buf) == 0)
199 desc = buf;
200
201 VERIFY(nvlist_add_string(unsup_feat, za.za_name,
202 desc) == 0);
203 }
204 }
205 }
206 zap_cursor_fini(&zc);
207
208 return (supported);
209 }
210
211 static int
212 feature_get_refcount(objset_t *os, uint64_t read_obj, uint64_t write_obj,
213 zfeature_info_t *feature, uint64_t *res)
214 {
215 int err;
216 uint64_t refcount;
217 uint64_t zapobj = feature->fi_can_readonly ? write_obj : read_obj;
218
219 ASSERT(0 != zapobj);
220
221 err = zap_lookup(os, zapobj, feature->fi_guid, sizeof (uint64_t), 1,
222 &refcount);
223 if (err != 0) {
224 if (err == ENOENT)
225 return (ENOTSUP);
226 else
227 return (err);
228 }
229 *res = refcount;
230 return (0);
231 }
232
233 static int
234 feature_do_action(objset_t *os, uint64_t read_obj, uint64_t write_obj,
235 uint64_t desc_obj, zfeature_info_t *feature, feature_action_t action,
236 dmu_tx_t *tx)
237 {
238 int error;
239 uint64_t refcount;
240 uint64_t zapobj = feature->fi_can_readonly ? write_obj : read_obj;
241
242 ASSERT(0 != zapobj);
243 ASSERT(zfeature_is_valid_guid(feature->fi_guid));
244
245 error = zap_lookup(os, zapobj, feature->fi_guid,
246 sizeof (uint64_t), 1, &refcount);
247
248 /*
249 * If we can't ascertain the status of the specified feature, an I/O
250 * error occurred.
251 */
252 if (error != 0 && error != ENOENT)
253 return (error);
254
255 switch (action) {
256 case FEATURE_ACTION_ENABLE:
257 /*
258 * If the feature is already enabled, ignore the request.
259 */
260 if (error == 0)
261 return (0);
262 refcount = 0;
263 break;
264 case FEATURE_ACTION_INCR:
265 if (error == ENOENT)
266 return (ENOTSUP);
267 if (refcount == UINT64_MAX)
268 return (EOVERFLOW);
269 refcount++;
270 break;
271 case FEATURE_ACTION_DECR:
272 if (error == ENOENT)
273 return (ENOTSUP);
274 if (refcount == 0)
275 return (EOVERFLOW);
276 refcount--;
277 break;
278 default:
279 ASSERT(0);
280 break;
281 }
282
283 if (action == FEATURE_ACTION_ENABLE) {
284 int i;
285
286 for (i = 0; feature->fi_depends[i] != NULL; i++) {
287 zfeature_info_t *dep = feature->fi_depends[i];
288
289 error = feature_do_action(os, read_obj, write_obj,
290 desc_obj, dep, FEATURE_ACTION_ENABLE, tx);
291 if (error != 0)
292 return (error);
293 }
294 }
295
296 error = zap_update(os, zapobj, feature->fi_guid,
297 sizeof (uint64_t), 1, &refcount, tx);
298 if (error != 0)
299 return (error);
300
301 if (action == FEATURE_ACTION_ENABLE) {
302 error = zap_update(os, desc_obj,
303 feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
304 feature->fi_desc, tx);
305 if (error != 0)
306 return (error);
307 }
308
309 if (action == FEATURE_ACTION_INCR && refcount == 1 && feature->fi_mos) {
310 spa_activate_mos_feature(dmu_objset_spa(os), feature->fi_guid);
311 }
312
313 if (action == FEATURE_ACTION_DECR && refcount == 0) {
314 spa_deactivate_mos_feature(dmu_objset_spa(os),
315 feature->fi_guid);
316 }
317
318 return (0);
319 }
320
321 void
322 spa_feature_create_zap_objects(spa_t *spa, dmu_tx_t *tx)
323 {
324 /*
325 * We create feature flags ZAP objects in two instances: during pool
326 * creation and during pool upgrade.
327 */
328 ASSERT(dsl_pool_sync_context(spa_get_dsl(spa)) || (!spa->spa_sync_on &&
329 tx->tx_txg == TXG_INITIAL));
330
331 spa->spa_feat_for_read_obj = zap_create_link(spa->spa_meta_objset,
332 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
333 DMU_POOL_FEATURES_FOR_READ, tx);
334 spa->spa_feat_for_write_obj = zap_create_link(spa->spa_meta_objset,
335 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
336 DMU_POOL_FEATURES_FOR_WRITE, tx);
337 spa->spa_feat_desc_obj = zap_create_link(spa->spa_meta_objset,
338 DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
339 DMU_POOL_FEATURE_DESCRIPTIONS, tx);
340 }
341
342 /*
343 * Enable any required dependencies, then enable the requested feature.
344 */
345 void
346 spa_feature_enable(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
347 {
348 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
349 VERIFY0(feature_do_action(spa->spa_meta_objset,
350 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
351 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_ENABLE, tx));
352 }
353
354 /*
355 * If the specified feature has not yet been enabled, this function returns
356 * ENOTSUP; otherwise, this function increments the feature's refcount (or
357 * returns EOVERFLOW if the refcount cannot be incremented). This function must
358 * be called from syncing context.
359 */
360 void
361 spa_feature_incr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
362 {
363 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
364 VERIFY0(feature_do_action(spa->spa_meta_objset,
365 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
366 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_INCR, tx));
367 }
368
369 /*
370 * If the specified feature has not yet been enabled, this function returns
371 * ENOTSUP; otherwise, this function decrements the feature's refcount (or
372 * returns EOVERFLOW if the refcount is already 0). This function must
373 * be called from syncing context.
374 */
375 void
376 spa_feature_decr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
377 {
378 ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
379 VERIFY0(feature_do_action(spa->spa_meta_objset,
380 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
381 spa->spa_feat_desc_obj, feature, FEATURE_ACTION_DECR, tx));
382 }
383
384 boolean_t
385 spa_feature_is_enabled(spa_t *spa, zfeature_info_t *feature)
386 {
387 int err;
388 uint64_t refcount;
389
390 if (spa_version(spa) < SPA_VERSION_FEATURES)
391 return (B_FALSE);
392
393 err = feature_get_refcount(spa->spa_meta_objset,
394 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
395 feature, &refcount);
396 ASSERT(err == 0 || err == ENOTSUP);
397 return (err == 0);
398 }
399
400 boolean_t
401 spa_feature_is_active(spa_t *spa, zfeature_info_t *feature)
402 {
403 int err;
404 uint64_t refcount;
405
406 if (spa_version(spa) < SPA_VERSION_FEATURES)
407 return (B_FALSE);
408
409 err = feature_get_refcount(spa->spa_meta_objset,
410 spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
411 feature, &refcount);
412 ASSERT(err == 0 || err == ENOTSUP);
413 return (err == 0 && refcount > 0);
414 }