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This patch implements two new messages that can be sent to the thin
pool target allowing it to take a snapshot of the _metadata_. This,
read-only snapshot can be accessed by userland, concurrently with the
live target.
Only one metadata snapshot can be held at a time. The pool's status
line will give the block location for the current msnap.
Since version 0.1.5 of the userland thin provisioning tools, the
thin_dump program displays the msnap as follows:
thin_dump -m <msnap root> <metadata dev>
Available here: https://github.com/jthornber/thin-provisioning-tools
Now that userland can access the metadata we can do various things
that have traditionally been kernel side tasks:
i) Incremental backups.
By using metadata snapshots we can work out what blocks have
changed over time. Combined with data snapshots we can ensure
the data doesn't change while we back it up.
A short proof of concept script can be found here:
https://github.com/jthornber/thinp-test-suite/blob/master/incremental_backup_example.rb
ii) Migration of thin devices from one pool to another.
iii) Merging snapshots back into an external origin.
iv) Asyncronous replication.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
177 lines
4.8 KiB
C
177 lines
4.8 KiB
C
/*
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* Copyright (C) 2010-2011 Red Hat, Inc.
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*
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* This file is released under the GPL.
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*/
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#ifndef DM_THIN_METADATA_H
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#define DM_THIN_METADATA_H
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#include "persistent-data/dm-block-manager.h"
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#define THIN_METADATA_BLOCK_SIZE 4096
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/*
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* The metadata device is currently limited in size.
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*
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* We have one block of index, which can hold 255 index entries. Each
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* index entry contains allocation info about 16k metadata blocks.
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*/
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#define THIN_METADATA_MAX_SECTORS (255 * (1 << 14) * (THIN_METADATA_BLOCK_SIZE / (1 << SECTOR_SHIFT)))
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/*
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* A metadata device larger than 16GB triggers a warning.
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*/
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#define THIN_METADATA_MAX_SECTORS_WARNING (16 * (1024 * 1024 * 1024 >> SECTOR_SHIFT))
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/*----------------------------------------------------------------*/
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struct dm_pool_metadata;
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struct dm_thin_device;
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/*
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* Device identifier
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*/
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typedef uint64_t dm_thin_id;
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/*
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* Reopens or creates a new, empty metadata volume.
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*/
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struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
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sector_t data_block_size);
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int dm_pool_metadata_close(struct dm_pool_metadata *pmd);
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/*
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* Compat feature flags. Any incompat flags beyond the ones
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* specified below will prevent use of the thin metadata.
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*/
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#define THIN_FEATURE_COMPAT_SUPP 0UL
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#define THIN_FEATURE_COMPAT_RO_SUPP 0UL
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#define THIN_FEATURE_INCOMPAT_SUPP 0UL
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/*
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* Device creation/deletion.
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*/
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int dm_pool_create_thin(struct dm_pool_metadata *pmd, dm_thin_id dev);
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/*
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* An internal snapshot.
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*
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* You can only snapshot a quiesced origin i.e. one that is either
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* suspended or not instanced at all.
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*/
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int dm_pool_create_snap(struct dm_pool_metadata *pmd, dm_thin_id dev,
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dm_thin_id origin);
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/*
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* Deletes a virtual device from the metadata. It _is_ safe to call this
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* when that device is open. Operations on that device will just start
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* failing. You still need to call close() on the device.
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*/
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int dm_pool_delete_thin_device(struct dm_pool_metadata *pmd,
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dm_thin_id dev);
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/*
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* Commits _all_ metadata changes: device creation, deletion, mapping
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* updates.
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*/
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int dm_pool_commit_metadata(struct dm_pool_metadata *pmd);
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/*
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* Set/get userspace transaction id.
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*/
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int dm_pool_set_metadata_transaction_id(struct dm_pool_metadata *pmd,
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uint64_t current_id,
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uint64_t new_id);
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int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd,
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uint64_t *result);
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/*
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* Hold/get root for userspace transaction.
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*
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* The metadata snapshot is a copy of the current superblock (minus the
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* space maps). Userland can access the data structures for READ
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* operations only. A small performance hit is incurred by providing this
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* copy of the metadata to userland due to extra copy-on-write operations
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* on the metadata nodes. Release this as soon as you finish with it.
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*/
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int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd);
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int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd);
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int dm_pool_get_metadata_snap(struct dm_pool_metadata *pmd,
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dm_block_t *result);
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/*
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* Actions on a single virtual device.
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*/
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/*
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* Opening the same device more than once will fail with -EBUSY.
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*/
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int dm_pool_open_thin_device(struct dm_pool_metadata *pmd, dm_thin_id dev,
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struct dm_thin_device **td);
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int dm_pool_close_thin_device(struct dm_thin_device *td);
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dm_thin_id dm_thin_dev_id(struct dm_thin_device *td);
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struct dm_thin_lookup_result {
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dm_block_t block;
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int shared;
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};
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/*
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* Returns:
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* -EWOULDBLOCK iff @can_block is set and would block.
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* -ENODATA iff that mapping is not present.
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* 0 success
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*/
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int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
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int can_block, struct dm_thin_lookup_result *result);
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/*
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* Obtain an unused block.
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*/
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int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result);
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/*
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* Insert or remove block.
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*/
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int dm_thin_insert_block(struct dm_thin_device *td, dm_block_t block,
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dm_block_t data_block);
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int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block);
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/*
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* Queries.
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*/
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int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
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dm_block_t *highest_mapped);
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int dm_thin_get_mapped_count(struct dm_thin_device *td, dm_block_t *result);
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int dm_pool_get_free_block_count(struct dm_pool_metadata *pmd,
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dm_block_t *result);
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int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
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dm_block_t *result);
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int dm_pool_get_metadata_dev_size(struct dm_pool_metadata *pmd,
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dm_block_t *result);
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int dm_pool_get_data_block_size(struct dm_pool_metadata *pmd, sector_t *result);
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int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result);
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/*
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* Returns -ENOSPC if the new size is too small and already allocated
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* blocks would be lost.
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*/
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int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_size);
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/*----------------------------------------------------------------*/
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#endif
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