FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/zfeature.c

     /*
      * CDDL HEADER START
      *
      * The contents of this file are subject to the terms of the
      * Common Development and Distribution License (the "License").
      * You may not use this file except in compliance with the License.
      *
      * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      * or https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    
    /*
     * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/zfeature.h>
    #include <sys/dmu.h>
    #include <sys/nvpair.h>
    #include <sys/zap.h>
    #include <sys/dmu_tx.h>
    #include "zfeature_common.h"
    #include <sys/spa_impl.h>
    
    /*
     * ZFS Feature Flags
     * -----------------
     *
     * ZFS feature flags are used to provide fine-grained versioning to the ZFS
     * on-disk format. Once enabled on a pool feature flags replace the old
     * spa_version() number.
     *
     * Each new on-disk format change will be given a uniquely identifying string
     * GUID rather than a version number. This avoids the problem of different
     * organizations creating new on-disk formats with the same version number. To
     * keep feature GUIDs unique they should consist of the reverse dns name of the
     * organization which implemented the feature and a short name for the feature,
     * separated by a colon (e.g. com.delphix:async_destroy).
     *
     * Reference Counts
     * ----------------
     *
     * Within each pool features can be in one of three states: disabled, enabled,
     * or active. These states are differentiated by a reference count stored on
     * disk for each feature:
     *
     *   1) If there is no reference count stored on disk the feature is disabled.
     *   2) If the reference count is 0 a system administrator has enabled the
     *      feature, but the feature has not been used yet, so no on-disk
     *      format changes have been made.
     *   3) If the reference count is greater than 0 the feature is active.
     *      The format changes required by the feature are currently on disk.
     *      Note that if the feature's format changes are reversed the feature
     *      may choose to set its reference count back to 0.
     *
     * Feature flags makes no differentiation between non-zero reference counts
     * for an active feature (e.g. a reference count of 1 means the same thing as a
     * reference count of 27834721), but feature implementations may choose to use
     * the reference count to store meaningful information. For example, a new RAID
     * implementation might set the reference count to the number of vdevs using
     * it. If all those disks are removed from the pool the feature goes back to
     * having a reference count of 0.
     *
     * It is the responsibility of the individual features to maintain a non-zero
     * reference count as long as the feature's format changes are present on disk.
     *
     * Dependencies
     * ------------
     *
     * Each feature may depend on other features. The only effect of this
     * relationship is that when a feature is enabled all of its dependencies are
     * automatically enabled as well. Any future work to support disabling of
     * features would need to ensure that features cannot be disabled if other
     * enabled features depend on them.
     *
     * On-disk Format
     * --------------
     *
     * When feature flags are enabled spa_version() is set to SPA_VERSION_FEATURES
     * (5000). In order for this to work the pool is automatically upgraded to
     * SPA_VERSION_BEFORE_FEATURES (28) first, so all pre-feature flags on disk
     * format changes will be in use.
     *
     * Information about features is stored in 3 ZAP objects in the pool's MOS.
     * These objects are linked to by the following names in the pool directory
     * object:
     *
     * 1) features_for_read: feature GUID -> reference count
     *    Features needed to open the pool for reading.
    * 2) features_for_write: feature GUID -> reference count
    *    Features needed to open the pool for writing.
    * 3) feature_descriptions: feature GUID -> descriptive string
    *    A human readable string.
    *
    * All enabled features appear in either features_for_read or
    * features_for_write, but not both.
    *
    * To open a pool in read-only mode only the features listed in
    * features_for_read need to be supported.
    *
    * To open the pool in read-write mode features in both features_for_read and
    * features_for_write need to be supported.
    *
    * Some features may be required to read the ZAP objects containing feature
    * information. To allow software to check for compatibility with these features
    * before the pool is opened their names must be stored in the label in a
    * new "features_for_read" entry (note that features that are only required
    * to write to a pool never need to be stored in the label since the
    * features_for_write ZAP object can be read before the pool is written to).
    * To save space in the label features must be explicitly marked as needing to
    * be written to the label. Also, reference counts are not stored in the label,
    * instead any feature whose reference count drops to 0 is removed from the
    * label.
    *
    * Adding New Features
    * -------------------
    *
    * Features must be registered in zpool_feature_init() function in
    * zfeature_common.c using the zfeature_register() function. This function
    * has arguments to specify if the feature should be stored in the
    * features_for_read or features_for_write ZAP object and if it needs to be
    * written to the label when active.
    *
    * Once a feature is registered it will appear as a "feature@<feature name>"
    * property which can be set by an administrator. Feature implementors should
    * use the spa_feature_is_enabled() and spa_feature_is_active() functions to
    * query the state of a feature and the spa_feature_incr() and
    * spa_feature_decr() functions to change an enabled feature's reference count.
    * Reference counts may only be updated in the syncing context.
    *
    * Features may not perform enable-time initialization. Instead, any such
    * initialization should occur when the feature is first used. This design
    * enforces that on-disk changes be made only when features are used. Code
    * should only check if a feature is enabled using spa_feature_is_enabled(),
    * not by relying on any feature specific metadata existing. If a feature is
    * enabled, but the feature's metadata is not on disk yet then it should be
    * created as needed.
    *
    * As an example, consider the com.delphix:async_destroy feature. This feature
    * relies on the existence of a bptree in the MOS that store blocks for
    * asynchronous freeing. This bptree is not created when async_destroy is
    * enabled. Instead, when a dataset is destroyed spa_feature_is_enabled() is
    * called to check if async_destroy is enabled. If it is and the bptree object
    * does not exist yet, the bptree object is created as part of the dataset
    * destroy and async_destroy's reference count is incremented to indicate it
    * has made an on-disk format change. Later, after the destroyed dataset's
    * blocks have all been asynchronously freed there is no longer any use for the
    * bptree object, so it is destroyed and async_destroy's reference count is
    * decremented back to 0 to indicate that it has undone its on-disk format
    * changes.
    */
   
   typedef enum {
           FEATURE_ACTION_INCR,
           FEATURE_ACTION_DECR,
   } feature_action_t;
   
   /*
    * Checks that the active features in the pool are supported by
    * this software.  Adds each unsupported feature (name -> description) to
    * the supplied nvlist.
    */
   boolean_t
   spa_features_check(spa_t *spa, boolean_t for_write,
       nvlist_t *unsup_feat, nvlist_t *enabled_feat)
   {
           objset_t *os = spa->spa_meta_objset;
           boolean_t supported;
           zap_cursor_t *zc;
           zap_attribute_t *za;
           uint64_t obj = for_write ?
               spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
           char *buf;
   
           zc = kmem_alloc(sizeof (zap_cursor_t), KM_SLEEP);
           za = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
           buf = kmem_alloc(MAXPATHLEN, KM_SLEEP);
   
           supported = B_TRUE;
           for (zap_cursor_init(zc, os, obj);
               zap_cursor_retrieve(zc, za) == 0;
               zap_cursor_advance(zc)) {
                   ASSERT(za->za_integer_length == sizeof (uint64_t) &&
                       za->za_num_integers == 1);
   
                   if (NULL != enabled_feat) {
                           fnvlist_add_uint64(enabled_feat, za->za_name,
                               za->za_first_integer);
                   }
   
                   if (za->za_first_integer != 0 &&
                       !zfeature_is_supported(za->za_name)) {
                           supported = B_FALSE;
   
                           if (NULL != unsup_feat) {
                                   const char *desc = "";
   
                                   if (zap_lookup(os, spa->spa_feat_desc_obj,
                                       za->za_name, 1, MAXPATHLEN, buf) == 0)
                                           desc = buf;
   
                                   VERIFY(nvlist_add_string(unsup_feat,
                                       za->za_name, desc) == 0);
                           }
                   }
           }
           zap_cursor_fini(zc);
   
           kmem_free(buf, MAXPATHLEN);
           kmem_free(za, sizeof (zap_attribute_t));
           kmem_free(zc, sizeof (zap_cursor_t));
   
           return (supported);
   }
   
   /*
    * Use an in-memory cache of feature refcounts for quick retrieval.
    *
    * Note: well-designed features will not need to use this; they should
    * use spa_feature_is_enabled() and spa_feature_is_active() instead.
    * However, this is non-static for zdb, zhack, and spa_add_feature_stats().
    */
   int
   feature_get_refcount(spa_t *spa, zfeature_info_t *feature, uint64_t *res)
   {
           ASSERT(VALID_FEATURE_FID(feature->fi_feature));
           if (spa->spa_feat_refcount_cache[feature->fi_feature] ==
               SPA_FEATURE_DISABLED) {
                   return (SET_ERROR(ENOTSUP));
           }
           *res = spa->spa_feat_refcount_cache[feature->fi_feature];
           return (0);
   }
   
   /*
    * Note: well-designed features will not need to use this; they should
    * use spa_feature_is_enabled() and spa_feature_is_active() instead.
    * However, this is non-static for zdb and zhack.
    */
   int
   feature_get_refcount_from_disk(spa_t *spa, zfeature_info_t *feature,
       uint64_t *res)
   {
           int err;
           uint64_t refcount;
           uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
               spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
   
           /*
            * If the pool is currently being created, the feature objects may not
            * have been allocated yet.  Act as though all features are disabled.
            */
           if (zapobj == 0)
                   return (SET_ERROR(ENOTSUP));
   
           err = zap_lookup(spa->spa_meta_objset, zapobj,
               feature->fi_guid, sizeof (uint64_t), 1, &refcount);
           if (err != 0) {
                   if (err == ENOENT)
                           return (SET_ERROR(ENOTSUP));
                   else
                           return (err);
           }
           *res = refcount;
           return (0);
   }
   
   
   static int
   feature_get_enabled_txg(spa_t *spa, zfeature_info_t *feature, uint64_t *res)
   {
           uint64_t enabled_txg_obj __maybe_unused = spa->spa_feat_enabled_txg_obj;
   
           ASSERT(zfeature_depends_on(feature->fi_feature,
               SPA_FEATURE_ENABLED_TXG));
   
           if (!spa_feature_is_enabled(spa, feature->fi_feature)) {
                   return (SET_ERROR(ENOTSUP));
           }
   
           ASSERT(enabled_txg_obj != 0);
   
           VERIFY0(zap_lookup(spa->spa_meta_objset, spa->spa_feat_enabled_txg_obj,
               feature->fi_guid, sizeof (uint64_t), 1, res));
   
           return (0);
   }
   
   /*
    * This function is non-static for zhack; it should otherwise not be used
    * outside this file.
    */
   void
   feature_sync(spa_t *spa, zfeature_info_t *feature, uint64_t refcount,
       dmu_tx_t *tx)
   {
           ASSERT(VALID_FEATURE_OR_NONE(feature->fi_feature));
           uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
               spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
           VERIFY0(zap_update(spa->spa_meta_objset, zapobj, feature->fi_guid,
               sizeof (uint64_t), 1, &refcount, tx));
   
           /*
            * feature_sync is called directly from zhack, allowing the
            * creation of arbitrary features whose fi_feature field may
            * be greater than SPA_FEATURES. When called from zhack, the
            * zfeature_info_t object's fi_feature field will be set to
            * SPA_FEATURE_NONE.
            */
           if (feature->fi_feature != SPA_FEATURE_NONE) {
                   uint64_t *refcount_cache =
                       &spa->spa_feat_refcount_cache[feature->fi_feature];
                   VERIFY3U(*refcount_cache, ==,
                       atomic_swap_64(refcount_cache, refcount));
           }
   
           if (refcount == 0)
                   spa_deactivate_mos_feature(spa, feature->fi_guid);
           else if (feature->fi_flags & ZFEATURE_FLAG_MOS)
                   spa_activate_mos_feature(spa, feature->fi_guid, tx);
   }
   
   /*
    * This function is non-static for zhack; it should otherwise not be used
    * outside this file.
    */
   void
   feature_enable_sync(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
   {
           uint64_t initial_refcount =
               (feature->fi_flags & ZFEATURE_FLAG_ACTIVATE_ON_ENABLE) ? 1 : 0;
           uint64_t zapobj = (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
               spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
   
           ASSERT(0 != zapobj);
           ASSERT(zfeature_is_valid_guid(feature->fi_guid));
           ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
   
           /*
            * If the feature is already enabled, ignore the request.
            */
           if (zap_contains(spa->spa_meta_objset, zapobj, feature->fi_guid) == 0)
                   return;
   
           for (int i = 0; feature->fi_depends[i] != SPA_FEATURE_NONE; i++)
                   spa_feature_enable(spa, feature->fi_depends[i], tx);
   
           VERIFY0(zap_update(spa->spa_meta_objset, spa->spa_feat_desc_obj,
               feature->fi_guid, 1, strlen(feature->fi_desc) + 1,
               feature->fi_desc, tx));
   
           feature_sync(spa, feature, initial_refcount, tx);
   
           if (spa_feature_is_enabled(spa, SPA_FEATURE_ENABLED_TXG)) {
                   uint64_t enabling_txg = dmu_tx_get_txg(tx);
   
                   if (spa->spa_feat_enabled_txg_obj == 0ULL) {
                           spa->spa_feat_enabled_txg_obj =
                               zap_create_link(spa->spa_meta_objset,
                               DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
                               DMU_POOL_FEATURE_ENABLED_TXG, tx);
                   }
                   spa_feature_incr(spa, SPA_FEATURE_ENABLED_TXG, tx);
   
                   VERIFY0(zap_add(spa->spa_meta_objset,
                       spa->spa_feat_enabled_txg_obj, feature->fi_guid,
                       sizeof (uint64_t), 1, &enabling_txg, tx));
           }
   
           /*
            * Errata #4 is mostly a problem with encrypted datasets, but it
            * is also a problem where the old encryption feature did not
            * depend on the bookmark_v2 feature. If the pool does not have
            * any encrypted datasets we can resolve this issue simply by
            * enabling this dependency.
            */
           if (spa->spa_errata == ZPOOL_ERRATA_ZOL_8308_ENCRYPTION &&
               spa_feature_is_enabled(spa, SPA_FEATURE_ENCRYPTION) &&
               !spa_feature_is_active(spa, SPA_FEATURE_ENCRYPTION) &&
               feature->fi_feature == SPA_FEATURE_BOOKMARK_V2)
                   spa->spa_errata = 0;
   
           /*
            * Convert the old on-disk error log to the new format when activating
            * the head_errlog feature.
            */
           if (feature->fi_feature == SPA_FEATURE_HEAD_ERRLOG)
                   spa_upgrade_errlog(spa, tx);
   }
   
   static void
   feature_do_action(spa_t *spa, spa_feature_t fid, feature_action_t action,
       dmu_tx_t *tx)
   {
           uint64_t refcount = 0;
           zfeature_info_t *feature = &spa_feature_table[fid];
           uint64_t zapobj __maybe_unused =
               (feature->fi_flags & ZFEATURE_FLAG_READONLY_COMPAT) ?
               spa->spa_feat_for_write_obj : spa->spa_feat_for_read_obj;
   
           ASSERT(VALID_FEATURE_FID(fid));
           ASSERT(0 != zapobj);
           ASSERT(zfeature_is_valid_guid(feature->fi_guid));
   
           ASSERT(dmu_tx_is_syncing(tx));
           ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
   
           VERIFY3U(feature_get_refcount(spa, feature, &refcount), !=, ENOTSUP);
   
           switch (action) {
           case FEATURE_ACTION_INCR:
                   VERIFY3U(refcount, !=, UINT64_MAX);
                   refcount++;
                   break;
           case FEATURE_ACTION_DECR:
                   VERIFY3U(refcount, !=, 0);
                   refcount--;
                   break;
           default:
                   ASSERT(0);
                   break;
           }
   
           feature_sync(spa, feature, refcount, tx);
   }
   
   void
   spa_feature_create_zap_objects(spa_t *spa, dmu_tx_t *tx)
   {
           /*
            * We create feature flags ZAP objects in two instances: during pool
            * creation and during pool upgrade.
            */
           ASSERT((!spa->spa_sync_on && tx->tx_txg == TXG_INITIAL) ||
               dsl_pool_sync_context(spa_get_dsl(spa)));
   
           spa->spa_feat_for_read_obj = zap_create_link(spa->spa_meta_objset,
               DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_FEATURES_FOR_READ, tx);
           spa->spa_feat_for_write_obj = zap_create_link(spa->spa_meta_objset,
               DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_FEATURES_FOR_WRITE, tx);
           spa->spa_feat_desc_obj = zap_create_link(spa->spa_meta_objset,
               DMU_OTN_ZAP_METADATA, DMU_POOL_DIRECTORY_OBJECT,
               DMU_POOL_FEATURE_DESCRIPTIONS, tx);
   }
   
   /*
    * Enable any required dependencies, then enable the requested feature.
    */
   void
   spa_feature_enable(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
   {
           ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
           ASSERT(VALID_FEATURE_FID(fid));
           feature_enable_sync(spa, &spa_feature_table[fid], tx);
   }
   
   void
   spa_feature_incr(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
   {
           feature_do_action(spa, fid, FEATURE_ACTION_INCR, tx);
   }
   
   void
   spa_feature_decr(spa_t *spa, spa_feature_t fid, dmu_tx_t *tx)
   {
           feature_do_action(spa, fid, FEATURE_ACTION_DECR, tx);
   }
   
   boolean_t
   spa_feature_is_enabled(spa_t *spa, spa_feature_t fid)
   {
           int err;
           uint64_t refcount = 0;
   
           ASSERT(VALID_FEATURE_FID(fid));
           if (spa_version(spa) < SPA_VERSION_FEATURES)
                   return (B_FALSE);
   
           err = feature_get_refcount(spa, &spa_feature_table[fid], &refcount);
           ASSERT(err == 0 || err == ENOTSUP);
           return (err == 0);
   }
   
   boolean_t
   spa_feature_is_active(spa_t *spa, spa_feature_t fid)
   {
           int err;
           uint64_t refcount = 0;
   
           ASSERT(VALID_FEATURE_FID(fid));
           if (spa_version(spa) < SPA_VERSION_FEATURES)
                   return (B_FALSE);
   
           err = feature_get_refcount(spa, &spa_feature_table[fid], &refcount);
           ASSERT(err == 0 || err == ENOTSUP);
           return (err == 0 && refcount > 0);
   }
   
   /*
    * For the feature specified by fid (which must depend on
    * SPA_FEATURE_ENABLED_TXG), return the TXG at which it was enabled in the
    * OUT txg argument.
    *
    * Returns B_TRUE if the feature is enabled, in which case txg will be filled
    * with the transaction group in which the specified feature was enabled.
    * Returns B_FALSE otherwise (i.e. if the feature is not enabled).
    */
   boolean_t
   spa_feature_enabled_txg(spa_t *spa, spa_feature_t fid, uint64_t *txg)
   {
           int err;
   
           ASSERT(VALID_FEATURE_FID(fid));
           if (spa_version(spa) < SPA_VERSION_FEATURES)
                   return (B_FALSE);
   
           err = feature_get_enabled_txg(spa, &spa_feature_table[fid], txg);
           ASSERT(err == 0 || err == ENOTSUP);
   
           return (err == 0);
   }

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