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zfs/module/zfs/zfeature.c

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/*
* 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 http://www.opensolaris.org/os/licensing.
* 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) {
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;
}
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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