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path: root/drivers/md/dm-snap.c
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* dm snapshot: use merge origin if snapshot invalidMikulas Patocka2009-12-10
| | | | | | | | | If the snapshot we are merging became invalid (e.g. it ran out of space) redirect all I/O directly to the origin device. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: report merge failure in statusMike Snitzer2009-12-10
| | | | | | | | Set 'merge_failed' flag if a snapshot fails to merge. Update snapshot_status() to report "Merge failed" if 'merge_failed' is set. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: merge consecutive chunks togetherMike Snitzer2009-12-10
| | | | | | | | | | | | | | | | | | | | | s->store->type->prepare_merge returns the number of chunks that can be copied linearly working backwards from the returned chunk number. For example, if it returns 3 chunks with old_chunk == 10 and new_chunk == 20, then chunk 20 can be copied to 10, chunk 19 to 9 and 18 to 8. Until now kcopyd only copied one chunk at a time. This patch now copies the full set at once. Consequently, snapshot_merge_process() needs to delay the merging of all chunks if any have writes in progress, not just the first chunk in the region that is to be merged. snapshot-merge's performance is now comparable to the original snapshot-origin target. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: trigger exceptions in remaining snapshots during mergeMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | When there is one merging snapshot and other non-merging snapshots, snapshot_merge_process() must make exceptions in the non-merging snapshots. Use a sequence count to resolve the race between I/O to chunks that are about to be merged. The count increases each time an exception reallocation finishes. Use wait_event() to wait until the count changes. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: delay merging a chunk until writes to it completeMikulas Patocka2009-12-10
| | | | | | | | | Track writes to chunks that are currently being merged and delay merging a chunk until all writes to that chunk finish. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: queue writes to chunks being mergedMikulas Patocka2009-12-10
| | | | | | | | | While a set of chunks is being merged, any overlapping writes need to be queued. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: add mergingMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | Merging is started when origin is resumed and it is stopped when origin is suspended or when the merging snapshot is destroyed or errors are detected. Merging is not yet interlocked with writes: this will be handled in subsequent patches. The code relies on callbacks from a private kcopyd thread. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: permit only one merge at onceMikulas Patocka2009-12-10
| | | | | | | | | Merging more than one snapshot is not supported, so prevent this happening. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: support barriers in snapshot merge targetMike Snitzer2009-12-10
| | | | | | | | | | | Sets num_flush_requests=2 to support flushing both the origin and cow devices used by the snapshot-merge target. Also, snapshot_ctr() now gets the origin device using FMODE_WRITE if the target is snapshot-merge (which writes to the origin device). Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: avoid allocating exceptions in mergeMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | | | | | The snapshot-merge target should not allocate new exceptions because the intent is to merge all of its exceptions as quickly and safely as possible. This patch introduces the snapshot-merge mapping function and updates __origin_write() so that it doesn't allocate exceptions on any snapshots that are being merged. If a write request to a merging snapshot device is to be dispatched directly to the origin (because the chunk is not remapped or was already merged), snapshot_merge_map() must make exceptions in other snapshots so calls do_origin(). Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: rework writing to originMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | | | | | | To track the completion of exceptions relating to the same location on the device, the current code selects one exception as primary_pe, links the other exceptions to it and uses reference counting to wait until all the reallocations are complete. It is considered too complicated to extend this code to handle the new snapshot-merge target, where sets of non-overlapping chunks would also need to become linked. Instead, a simpler (but less efficient) approach is taken. Bios are linked to one exception. When it completes, bios are simply retried, and if other related exceptions are still outstanding, they'll get queued again to wait for another one. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: add merge targetMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | | | The snapshot-merge target allows a snapshot to be merged back into the snapshot's origin device. One anticipated use of snapshot merging is the rollback of filesystems to back out problematic system upgrades. This patch adds snapshot-merge target management to both dm_snapshot_init() and dm_snapshot_exit(). As an initial place-holder, snapshot-merge is identical to the snapshot target. Documentation is provided. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: create function for chunk_is_tracked waitMike Snitzer2009-12-10
| | | | | | | | | | | | Move the __chunk_is_tracked() loop into a separate function as we will also need to call it from the write path in the rare case of conflicting writes to the same chunk. Originally introduced in commit a8d41b59f3f5a7ac19452ef442a7fc1b5fa17366 ("dm snapshot: fix race during exception creation"). Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: make bio optional in __origin_writeMikulas Patocka2009-12-10
| | | | | | | | | | | | To support the merging of snapshots back into their origin we need to trigger exceptions in other snapshots not being merged without any incoming bio on the origin device. The bio parameter to __origin_write() becomes optional and the sector needs supplying separately. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: allow live exception store handover between tablesMike Snitzer2009-12-10
| | | | | | | | | | | | | | | | | | | | | | | | | Permit in-use snapshot exception data to be 'handed over' from one snapshot instance to another. This is a pre-requisite for patches that allow the changes made in a snapshot device to be merged back into its origin device and also allows device resizing. The basic call sequence is: dmsetup load new_snapshot (referencing the existing in-use cow device) - the ctr code detects that the cow is already in use and allows the two snapshot target instances to be linked together dmsetup suspend original_snapshot dmsetup resume new_snapshot - the new_snapshot becomes live, and if anything now tries to access the original one it will receive -EIO dmsetup remove original_snapshot (There can only be two snapshot targets referencing the same cow device simultaneously.) Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: track suspended state in targetMike Snitzer2009-12-10
| | | | | | | | | | | | | Keep track of whether or not the device is suspended within the snapshot target module, the same as we do in dm-raid1. We will use this later to enforce the correct sequence of ioctls to transfer the in-core exceptions from a snapshot target instance in one table to a replacement one capable of merging them back into the origin. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: move cow ref from exception store to snap coreMike Snitzer2009-12-10
| | | | | | | | | | | | | | Store the reference to the snapshot cow device in the core snapshot code instead of each exception store. It can be accessed through the new function dm_snap_cow(). Exception stores should each now maintain a reference to their parent snapshot struct. This is cleaner and makes part of the forthcoming snapshot merge code simpler. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Reviewed-by: Jonathan Brassow <jbrassow@redhat.com> Cc: Mikulas Patocka <mpatocka@redhat.com>
* dm snapshot: add allocated metadata to snapshot statusMike Snitzer2009-12-10
| | | | | | | | | | | | Add number of sectors used by metadata to the end of the snapshot's status line. Renamed dm_exception_store_type's 'fraction_full' to 'usage'. Renamed arguments to be clearer about what is being returned. Also added 'metadata_sectors'. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: rename exception functionsJon Brassow2009-12-10
| | | | | | | | | Rename exception functions. Preparing to pull them out of dm-snap.c for broader use. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: rename exception_table to dm_exception_tableJon Brassow2009-12-10
| | | | | | | | Rename exception_table for broader use outside dm-snap.c Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: rename dm_snap_exception to dm_exceptionJon Brassow2009-12-10
| | | | | | | | | | | The exception structure is not necessarily just a snapshot element (especially after we pull it out of dm-snap.c). Renaming appropriately. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: consolidate insert exception functionsJon Brassow2009-12-10
| | | | | | | | | | Consolidate the insert_*exception functions. 'insert_completed_exception' already contains all the logic to handle 'insert_exception' (via check for a hash_shift of 0), so remove redundant function. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: abstract minimum_chunk_size fnMikulas Patocka2009-12-10
| | | | | | | | | | | The origin needs to find minimum chunksize of all snapshots. This logic is moved to a separate function because it will be used at another place in the snapshot merge patches. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Reviewed-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: cope with chunk size larger than originMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | | Under some special conditions the snapshot hash_size is calculated as zero. This patch instead sets a minimum value of 64, the same as for the pending exception table. rounddown_pow_of_two(0) is an undefined operation (it expands to shift by -1). init_exception_table with an argument of 0 would fail with -ENOMEM. The way to trigger the problem is to create a snapshot with a chunk size that is larger than the origin device. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: only take lock for statustype info not tableMikulas Patocka2009-12-10
| | | | | | | | | | | | | | | Take snapshot lock only for STATUSTYPE_INFO, not STATUSTYPE_TABLE. Commit 4c6fff445d7aa753957856278d4d93bcad6e2c14 (dm-snapshot-lock-snapshot-while-supplying-status.patch) introduced this use of the lock, but userspace applications using libdevmapper have been found to request STATUSTYPE_TABLE while the device is suspended and the lock is already held, leading to deadlock. Since the lock is not necessary in this case, don't try to take it. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: use unsigned integer chunk sizeMikulas Patocka2009-10-16
| | | | | | | | | | | | | | Use unsigned integer chunk size. Maximum chunk size is 512kB, there won't ever be need to use 4GB chunk size, so the number can be 32-bit. This fixes compiler failure on 32-bit systems with large block devices. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Reviewed-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: lock snapshot while supplying statusMikulas Patocka2009-10-16
| | | | | | | | | | This patch locks the snapshot when returning status. It fixes a race when it could return an invalid number of free chunks if someone was simultaneously modifying it. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: require non zero chunk size by end of ctrMikulas Patocka2009-10-16
| | | | | | | | | | | | If we are creating snapshot with memory-stored exception store, fail if the user didn't specify chunk size. Zero chunk size would probably crash a lot of places in the rest of snapshot code. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Reviewed-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: free exception store on init failureJonathan Brassow2009-10-16
| | | | | | | | | | | | While initializing the snapshot module, if we fail to register the snapshot target then we must back-out the exception store module initialization. Cc: stable@kernel.org Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Reviewed-by: Mikulas Patocka <mpatocka@redhat.com> Reviewed-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: sort by chunk size to fix raceMikulas Patocka2009-10-16
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Avoid a race causing corruption when snapshots of the same origin have different chunk sizes by sorting the internal list of snapshots by chunk size, largest first. https://bugzilla.redhat.com/show_bug.cgi?id=182659 For example, let's have two snapshots with different chunk sizes. The first snapshot (1) has small chunk size and the second snapshot (2) has large chunk size. Let's have chunks A, B, C in these snapshots: snapshot1: ====A==== ====B==== snapshot2: ==========C========== (Chunk size is a power of 2. Chunks are aligned.) A write to the origin at a position within A and C comes along. It triggers reallocation of A, then reallocation of C and links them together using A as the 'primary' exception. Then another write to the origin comes along at a position within B and C. It creates pending exception for B. C already has a reallocation in progress and it already has a primary exception (A), so nothing is done to it: B and C are not linked. If the reallocation of B finishes before the reallocation of C, because there is no link with the pending exception for C it does not know to wait for it and, the second write is dispatched to the origin and causes data corruption in the chunk C in snapshot2. To avoid this situation, we maintain snapshots sorted in descending order of chunk size. This leads to a guaranteed ordering on the links between the pending exceptions and avoids the problem explained above - both A and B now get linked to C. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: implement iterate devicesMike Snitzer2009-09-04
| | | | | | | | | | | | | | | | | | Implement the .iterate_devices for the origin and snapshot targets. dm-snapshot's lack of .iterate_devices resulted in the inability to properly establish queue_limits for both targets. With 4K sector drives: an unfortunate side-effect of not establishing proper limits in either targets' DM device was that IO to the devices would fail even though both had been created without error. Commit af4874e03ed82f050d5872d8c39ce64bf16b5c38 ("dm target:s introduce iterate devices fn") in 2.6.31-rc1 should have implemented .iterate_devices for dm-snap.c's origin and snapshot targets. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: support barriersMikulas Patocka2009-06-22
| | | | | | | | | | Flush support for dm-snapshot target. This patch just forwards the flush request to either the origin or the snapshot device. (It doesn't flush exception store metadata.) Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* block: move bio list helpers into bio.hChristoph Hellwig2009-04-15
| | | | | | | | | It's used by DM and MD and generally useful, so move the bio list helpers into bio.h. Signed-off-by: Christoph Hellwig <hch@lst.de> Acked-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
* dm snapshot: move status to exception storeJonathan Brassow2009-04-02
| | | | | | | | | | | Let the exception store types print out their status through the new API, rather than having the snapshot code do it. Adjust the buffer position to allow for the preceding DMEMIT in the arguments to type->status(). Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: move ctr parsing to exception storeJonathan Brassow2009-04-02
| | | | | | | | First step of having the exception stores parse their own arguments - generalizing the interface. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: use DMEMIT macro for statusJonathan Brassow2009-04-02
| | | | | | | | Use DMEMIT in place of snprintf. This makes it easier later when other modules are helping to populate our status output. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: remove dm_snap headerJonathan Brassow2009-04-02
| | | | | | | | Move some of the last bits from dm-snap.h into dm-snap.c where they belong and remove dm-snap.h. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: remove dm_snap header useJonathan Brassow2009-04-02
| | | | | | | Move useful functions out of dm-snap.h and stop using dm-snap.h. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm exception store: move cow pointerJonathan Brassow2009-04-02
| | | | | | | Move COW device from snapshot to exception store. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm exception store: move chunk_fieldsJonathan Brassow2009-04-02
| | | | | | | Move chunk fields from snapshot to exception store. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm exception store: move dm_target pointerJonathan Brassow2009-04-02
| | | | | | | Move target pointer from snapshot to exception store. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm exception store: introduce registryJonathan Brassow2009-04-02
| | | | | | | Move exception stores into a registry. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm exception store: separate type from instanceJonathan Brassow2009-04-02
| | | | | | | Introduce struct dm_exception_store_type. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: avoid having two exceptions for the same chunkMikulas Patocka2009-04-02
| | | | | | | | | | | | | | | | | | | | | | We need to check if the exception was completed after dropping the lock. After regaining the lock, __find_pending_exception checks if the exception was already placed into &s->pending hash. But we don't check if the exception was already completed and placed into &s->complete hash. If the process waiting in alloc_pending_exception was delayed at this point because of a scheduling latency and the exception was meanwhile completed, we'd miss that and allocate another pending exception for already completed chunk. It would lead to a situation where two records for the same chunk exist and potential data corruption because multiple snapshot I/Os to the affected chunk could be redirected to different locations in the snapshot. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: avoid dropping lock in __find_pending_exceptionMikulas Patocka2009-04-02
| | | | | | | | | It is uncommon and bug-prone to drop a lock in a function that is called with the lock held, so this is moved to the caller. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: refactor __find_pending_exceptionMikulas Patocka2009-04-02
| | | | | | | | | Move looking-up of a pending exception from __find_pending_exception to another function. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: extend exception store functionsJonathan Brassow2009-01-05
| | | | | | | | | Supply dm_add_exception as a callback to the read_metadata function. Add a status function ready for a later patch and name the functions consistently. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: split out exception store implementationsAlasdair G Kergon2009-01-05
| | | | | | | | Move the existing snapshot exception store implementations out into separate files. Later patches will place these behind a new interface in preparation for alternative implementations. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm snapshot: separate out exception store interfaceJonathan Brassow2009-01-05
| | | | | | | | | | | | | Pull structures that bridge the gap between snapshot and exception store out of dm-snap.h and put them in a new .h file - dm-exception-store.h. This file will define the API for new exception stores. Ultimately, dm-snap.h is unnecessary, since only dm-snap.c should be using it. Signed-off-by: Jonathan Brassow <jbrassow@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm: consolidate target deregistration error handlingMikulas Patocka2009-01-05
| | | | | | | | | | | | | | | | | | | | Change dm_unregister_target to return void and use BUG() for error reporting. dm_unregister_target can only fail because of programming bug in the target driver. It can't fail because of user's behavior or disk errors. This patch changes unregister_target to return void and use BUG if someone tries to unregister non-registered target or unregister target that is in use. This patch removes code duplication (testing of error codes in all dm targets) and reports bugs in just one place, in dm_unregister_target. In some target drivers, these return codes were ignored, which could lead to a situation where bugs could be missed. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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