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path: root/fs/btrfs/raid56.c
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2014-12-03Btrfs, raid56: fix use-after-free problem in the final device replace ↵Miao Xie
procedure on raid56 The commit c404e0dc (Btrfs: fix use-after-free in the finishing procedure of the device replace) fixed a use-after-free problem which happened when removing the source device at the end of device replace, but at that time, btrfs didn't support device replace on raid56, so we didn't fix the problem on the raid56 profile. Currently, we implemented device replace for raid56, so we need kick that problem out before we enable that function for raid56. The fix method is very simple, we just increase the bio per-cpu counter before we submit a raid56 io, and decrease the counter when the raid56 io ends. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, replace: write raid56 parity into the replace target deviceMiao Xie
This function reused the code of parity scrub, and we just write the right parity or corrected parity into the target device before the parity scrub end. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, replace: write dirty pages into the replace target deviceMiao Xie
The implementation is simple: - In order to avoid changing the code logic of btrfs_map_bio and RAID56, we add the stripes of the replace target devices at the end of the stripe array in btrfs bio, and we sort those target device stripes in the array. And we keep the number of the target device stripes in the btrfs bio. - Except write operation on RAID56, all the other operation don't take the target device stripes into account. - When we do write operation, we read the data from the common devices and calculate the parity. Then write the dirty data and new parity out, at this time, we will find the relative replace target stripes and wirte the relative data into it. Note: The function that copying old data on the source device to the target device was implemented in the past, it is similar to the other RAID type. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, raid56: support parity scrub on raid56Miao Xie
The implementation is: - Read and check all the data with checksum in the same stripe. All the data which has checksum is COW data, and we are sure that it is not changed though we don't lock the stripe. because the space of that data just can be reclaimed after the current transction is committed, and then the fs can use it to store the other data, but when doing scrub, we hold the current transaction, that is that data can not be recovered, it is safe that read and check it out of the stripe lock. - Lock the stripe - Read out all the data without checksum and parity The data without checksum and the parity may be changed if we don't lock the stripe, so we need read it in the stripe lock context. - Check the parity - Re-calculate the new parity and write back it if the old parity is not right - Unlock the stripe If we can not read out the data or the data we read is corrupted, we will try to repair it. If the repair fails. we will mark the horizontal sub-stripe(pages on the same horizontal) as corrupted sub-stripe, and we will skip the parity check and repair of that horizontal sub-stripe. And in order to skip the horizontal sub-stripe that has no data, we introduce a bitmap. If there is some data on the horizontal sub-stripe, we will the relative bit to 1, and when we check and repair the parity, we will skip those horizontal sub-stripes that the relative bits is 0. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, raid56: use a variant to record the operation typeMiao Xie
We will introduce new operation type later, if we still use integer variant as bool variant to record the operation type, we would add new variant and increase the size of raid bio structure. It is not good, by this patch, we define different number for different operation, and we can just use a variant to record the operation type. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, scrub: repair the common data on RAID5/6 if it is corruptedMiao Xie
This patch implement the RAID5/6 common data repair function, the implementation is similar to the scrub on the other RAID such as RAID1, the differentia is that we don't read the data from the mirror, we use the data repair function of RAID5/6. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-12-03Btrfs, raid56: don't change bbio and raid_mapMiao Xie
Because we will reuse bbio and raid_map during the scrub later, it is better that we don't change any variant of bbio and don't free it at the end of IO request. So we introduced similar variants into the raid bio, and don't access those bbio's variants any more. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
2014-09-17btrfs: use DIV_ROUND_UP instead of open-coded variantsDavid Sterba
The form (value + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT is equivalent to (value + PAGE_CACHE_SIZE - 1) / PAGE_CACHE_SIZE The rest is a simple subsitution, no difference in the generated assembly code. Signed-off-by: David Sterba <dsterba@suse.cz> Signed-off-by: Chris Mason <clm@fb.com>
2014-08-24Btrfs: fix task hang under heavy compressed writeLiu Bo
This has been reported and discussed for a long time, and this hang occurs in both 3.15 and 3.16. Btrfs now migrates to use kernel workqueue, but it introduces this hang problem. Btrfs has a kind of work queued as an ordered way, which means that its ordered_func() must be processed in the way of FIFO, so it usually looks like -- normal_work_helper(arg) work = container_of(arg, struct btrfs_work, normal_work); work->func() <---- (we name it work X) for ordered_work in wq->ordered_list ordered_work->ordered_func() ordered_work->ordered_free() The hang is a rare case, first when we find free space, we get an uncached block group, then we go to read its free space cache inode for free space information, so it will file a readahead request btrfs_readpages() for page that is not in page cache __do_readpage() submit_extent_page() btrfs_submit_bio_hook() btrfs_bio_wq_end_io() submit_bio() end_workqueue_bio() <--(ret by the 1st endio) queue a work(named work Y) for the 2nd also the real endio() So the hang occurs when work Y's work_struct and work X's work_struct happens to share the same address. A bit more explanation, A,B,C -- struct btrfs_work arg -- struct work_struct kthread: worker_thread() pick up a work_struct from @worklist process_one_work(arg) worker->current_work = arg; <-- arg is A->normal_work worker->current_func(arg) normal_work_helper(arg) A = container_of(arg, struct btrfs_work, normal_work); A->func() A->ordered_func() A->ordered_free() <-- A gets freed B->ordered_func() submit_compressed_extents() find_free_extent() load_free_space_inode() ... <-- (the above readhead stack) end_workqueue_bio() btrfs_queue_work(work C) B->ordered_free() As if work A has a high priority in wq->ordered_list and there are more ordered works queued after it, such as B->ordered_func(), its memory could have been freed before normal_work_helper() returns, which means that kernel workqueue code worker_thread() still has worker->current_work pointer to be work A->normal_work's, ie. arg's address. Meanwhile, work C is allocated after work A is freed, work C->normal_work and work A->normal_work are likely to share the same address(I confirmed this with ftrace output, so I'm not just guessing, it's rare though). When another kthread picks up work C->normal_work to process, and finds our kthread is processing it(see find_worker_executing_work()), it'll think work C as a collision and skip then, which ends up nobody processing work C. So the situation is that our kthread is waiting forever on work C. Besides, there're other cases that can lead to deadlock, but the real problem is that all btrfs workqueue shares one work->func, -- normal_work_helper, so this makes each workqueue to have its own helper function, but only a wraper pf normal_work_helper. With this patch, I no long hit the above hang. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-06-28Btrfs: fix crash when mounting raid5 btrfs with missing disksLiu Bo
The reproducer is $ mkfs.btrfs D1 D2 D3 -mraid5 $ mkfs.ext4 D2 && mkfs.ext4 D3 $ mount D1 /btrfs -odegraded ------------------- [ 87.672992] ------------[ cut here ]------------ [ 87.673845] kernel BUG at fs/btrfs/raid56.c:1828! ... [ 87.673845] RIP: 0010:[<ffffffff813efc7e>] [<ffffffff813efc7e>] __raid_recover_end_io+0x4ae/0x4d0 ... [ 87.673845] Call Trace: [ 87.673845] [<ffffffff8116bbc6>] ? mempool_free+0x36/0xa0 [ 87.673845] [<ffffffff813f0255>] raid_recover_end_io+0x75/0xa0 [ 87.673845] [<ffffffff81447c5b>] bio_endio+0x5b/0xa0 [ 87.673845] [<ffffffff81447cb2>] bio_endio_nodec+0x12/0x20 [ 87.673845] [<ffffffff81374621>] end_workqueue_fn+0x41/0x50 [ 87.673845] [<ffffffff813ad2aa>] normal_work_helper+0xca/0x2c0 [ 87.673845] [<ffffffff8108ba2b>] process_one_work+0x1eb/0x530 [ 87.673845] [<ffffffff8108b9c9>] ? process_one_work+0x189/0x530 [ 87.673845] [<ffffffff8108c15b>] worker_thread+0x11b/0x4f0 [ 87.673845] [<ffffffff8108c040>] ? rescuer_thread+0x290/0x290 [ 87.673845] [<ffffffff810939c4>] kthread+0xe4/0x100 [ 87.673845] [<ffffffff810938e0>] ? kthread_create_on_node+0x220/0x220 [ 87.673845] [<ffffffff817e7c7c>] ret_from_fork+0x7c/0xb0 [ 87.673845] [<ffffffff810938e0>] ? kthread_create_on_node+0x220/0x220 ------------------- It's because that we miscalculate @rbio->bbio->error so that it doesn't reach maximum of tolerable errors while it should have. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Tested-by: Satoru Takeuchi<takeuchi_satoru@jp.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-04-04Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs Pull btrfs changes from Chris Mason: "This is a pretty long stream of bug fixes and performance fixes. Qu Wenruo has replaced the btrfs async threads with regular kernel workqueues. We'll keep an eye out for performance differences, but it's nice to be using more generic code for this. We still have some corruption fixes and other patches coming in for the merge window, but this batch is tested and ready to go" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs: (108 commits) Btrfs: fix a crash of clone with inline extents's split btrfs: fix uninit variable warning Btrfs: take into account total references when doing backref lookup Btrfs: part 2, fix incremental send's decision to delay a dir move/rename Btrfs: fix incremental send's decision to delay a dir move/rename Btrfs: remove unnecessary inode generation lookup in send Btrfs: fix race when updating existing ref head btrfs: Add trace for btrfs_workqueue alloc/destroy Btrfs: less fs tree lock contention when using autodefrag Btrfs: return EPERM when deleting a default subvolume Btrfs: add missing kfree in btrfs_destroy_workqueue Btrfs: cache extent states in defrag code path Btrfs: fix deadlock with nested trans handles Btrfs: fix possible empty list access when flushing the delalloc inodes Btrfs: split the global ordered extents mutex Btrfs: don't flush all delalloc inodes when we doesn't get s_umount lock Btrfs: reclaim delalloc metadata more aggressively Btrfs: remove unnecessary lock in may_commit_transaction() Btrfs: remove the unnecessary flush when preparing the pages Btrfs: just do dirty page flush for the inode with compression before direct IO ...
2014-03-10btrfs: Cleanup the "_struct" suffix in btrfs_workequeueQu Wenruo
Since the "_struct" suffix is mainly used for distinguish the differnt btrfs_work between the original and the newly created one, there is no need using the suffix since all btrfs_workers are changed into btrfs_workqueue. Also this patch fixed some codes whose code style is changed due to the too long "_struct" suffix. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Replace fs_info->rmw_workers workqueue with btrfs_workqueue.Qu Wenruo
Replace the fs_info->rmw_workers with the newly created btrfs_workqueue. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2013-11-23block: Abstract out bvec iteratorKent Overstreet
Immutable biovecs are going to require an explicit iterator. To implement immutable bvecs, a later patch is going to add a bi_bvec_done member to this struct; for now, this patch effectively just renames things. Signed-off-by: Kent Overstreet <kmo@daterainc.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: "Ed L. Cashin" <ecashin@coraid.com> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Lars Ellenberg <drbd-dev@lists.linbit.com> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Yehuda Sadeh <yehuda@inktank.com> Cc: Sage Weil <sage@inktank.com> Cc: Alex Elder <elder@inktank.com> Cc: ceph-devel@vger.kernel.org Cc: Joshua Morris <josh.h.morris@us.ibm.com> Cc: Philip Kelleher <pjk1939@linux.vnet.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Neil Brown <neilb@suse.de> Cc: Alasdair Kergon <agk@redhat.com> Cc: Mike Snitzer <snitzer@redhat.com> Cc: dm-devel@redhat.com Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: linux390@de.ibm.com Cc: Boaz Harrosh <bharrosh@panasas.com> Cc: Benny Halevy <bhalevy@tonian.com> Cc: "James E.J. Bottomley" <JBottomley@parallels.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Chris Mason <chris.mason@fusionio.com> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Cc: Jaegeuk Kim <jaegeuk.kim@samsung.com> Cc: Steven Whitehouse <swhiteho@redhat.com> Cc: Dave Kleikamp <shaggy@kernel.org> Cc: Joern Engel <joern@logfs.org> Cc: Prasad Joshi <prasadjoshi.linux@gmail.com> Cc: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp> Cc: Mark Fasheh <mfasheh@suse.com> Cc: Joel Becker <jlbec@evilplan.org> Cc: Ben Myers <bpm@sgi.com> Cc: xfs@oss.sgi.com Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Len Brown <len.brown@intel.com> Cc: Pavel Machek <pavel@ucw.cz> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Cc: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com> Cc: Ben Hutchings <ben@decadent.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Guo Chao <yan@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Cc: Asai Thambi S P <asamymuthupa@micron.com> Cc: Selvan Mani <smani@micron.com> Cc: Sam Bradshaw <sbradshaw@micron.com> Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn> Cc: "Roger Pau Monné" <roger.pau@citrix.com> Cc: Jan Beulich <jbeulich@suse.com> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com> Cc: Ian Campbell <Ian.Campbell@citrix.com> Cc: Sebastian Ott <sebott@linux.vnet.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Jiang Liu <jiang.liu@huawei.com> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Jerome Marchand <jmarchand@redhat.com> Cc: Joe Perches <joe@perches.com> Cc: Peng Tao <tao.peng@emc.com> Cc: Andy Adamson <andros@netapp.com> Cc: fanchaoting <fanchaoting@cn.fujitsu.com> Cc: Jie Liu <jeff.liu@oracle.com> Cc: Sunil Mushran <sunil.mushran@gmail.com> Cc: "Martin K. Petersen" <martin.petersen@oracle.com> Cc: Namjae Jeon <namjae.jeon@samsung.com> Cc: Pankaj Kumar <pankaj.km@samsung.com> Cc: Dan Magenheimer <dan.magenheimer@oracle.com> Cc: Mel Gorman <mgorman@suse.de>6
2013-11-11btrfs: remove fs/btrfs/compat.hZach Brown
fs/btrfs/compat.h only contained trivial macro wrappers of drop_nlink() and inc_nlink(). This doesn't belong in mainline. Signed-off-by: Zach Brown <zab@redhat.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-09-01Btrfs, raid56: fix memory leak when allocating pages for p/q stripes failedMiao Xie
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-09-01btrfs/raid56: fix and cleanup some error pathsDan Carpenter
The alloc_rbio() frees "raid_map" and "bbio" on error, so there is a potential double free bug in raid56_parity_write(). The raid56_parity_write() and raid56_parity_recover() functions should still free "raid_map" and "bbio" on error if other errors occur though, so I have added some more calls to kfree(). Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-05-17Btrfs: use a btrfs bioset instead of abusing bio internalsChris Mason
Btrfs has been pointer tagging bi_private and using bi_bdev to store the stripe index and mirror number of failed IOs. As bios bubble back up through the call chain, we use these to decide if and how to retry our IOs. They are also used to count IO failures on a per device basis. Recently a bio tracepoint was added lead to crashes because we were abusing bi_bdev. This commit adds a btrfs bioset, and creates explicit fields for the mirror number and stripe index. The plan is to extend this structure for all of the fields currently in struct btrfs_bio, which will mean one less kmalloc in our IO path. Signed-off-by: Chris Mason <chris.mason@fusionio.com> Reported-by: Tejun Heo <tj@kernel.org>
2013-05-06btrfs: make static code static & remove dead codeEric Sandeen
Big patch, but all it does is add statics to functions which are in fact static, then remove the associated dead-code fallout. removed functions: btrfs_iref_to_path() __btrfs_lookup_delayed_deletion_item() __btrfs_search_delayed_insertion_item() __btrfs_search_delayed_deletion_item() find_eb_for_page() btrfs_find_block_group() range_straddles_pages() extent_range_uptodate() btrfs_file_extent_length() btrfs_scrub_cancel_devid() btrfs_start_transaction_lflush() btrfs_print_tree() is left because it is used for debugging. btrfs_start_transaction_lflush() and btrfs_reada_detach() are left for symmetry. ulist.c functions are left, another patch will take care of those. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
2013-03-03btrfs/raid56: Add missing #include <linux/vmalloc.h>Geert Uytterhoeven
tilegx_defconfig: fs/btrfs/raid56.c: In function 'btrfs_alloc_stripe_hash_table': fs/btrfs/raid56.c:206:3: error: implicit declaration of function 'vzalloc' [-Werror=implicit-function-declaration] fs/btrfs/raid56.c:206:9: warning: assignment makes pointer from integer without a cast [enabled by default] fs/btrfs/raid56.c:226:4: error: implicit declaration of function 'vfree' [-Werror=implicit-function-declaration] Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-03-01btrfs: try harder to allocate raid56 stripe cacheDavid Sterba
The stripe hash table is large, starting with allocation order 4 and can go as high as order 7 in case lock debugging is turned on and structure padding happens. Observed mount failure: mount: page allocation failure: order:7, mode:0x200050 Pid: 8234, comm: mount Tainted: G W 3.8.0-default+ #267 Call Trace: [<ffffffff81114353>] warn_alloc_failed+0xf3/0x140 [<ffffffff811171d2>] ? __alloc_pages_direct_compact+0x92/0x250 [<ffffffff81117ac3>] __alloc_pages_nodemask+0x733/0x9d0 [<ffffffff81152878>] ? cache_alloc_refill+0x3f8/0x840 [<ffffffff811528bc>] cache_alloc_refill+0x43c/0x840 [<ffffffff811302eb>] ? is_kernel_percpu_address+0x4b/0x90 [<ffffffffa00a00ac>] ? btrfs_alloc_stripe_hash_table+0x5c/0x130 [btrfs] [<ffffffff811531d7>] kmem_cache_alloc_trace+0x247/0x270 [<ffffffffa00a00ac>] btrfs_alloc_stripe_hash_table+0x5c/0x130 [btrfs] [<ffffffffa003133f>] open_ctree+0xb2f/0x1f90 [btrfs] [<ffffffff81397289>] ? string+0x49/0xe0 [<ffffffff813987b3>] ? vsnprintf+0x443/0x5d0 [<ffffffffa0007cb6>] btrfs_mount+0x526/0x600 [btrfs] [<ffffffff8115127c>] ? cache_alloc_debugcheck_after+0x4c/0x200 [<ffffffff81162b90>] mount_fs+0x20/0xe0 [<ffffffff8117db26>] vfs_kern_mount+0x76/0x120 [<ffffffff811801b6>] do_mount+0x386/0x980 [<ffffffff8112a5cb>] ? strndup_user+0x5b/0x80 [<ffffffff81180840>] sys_mount+0x90/0xe0 [<ffffffff81962e99>] system_call_fastpath+0x16/0x1b Signed-off-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
2013-02-01Btrfs: add a plugging callback to raid56 writesChris Mason
Buffered writes and DIRECT_IO writes will often break up big contiguous changes to the file into sub-stripe writes. This adds a plugging callback to gather those smaller writes full stripe writes. Example on flash: fio job to do 64K writes in batches of 3 (which makes a full stripe): With plugging: 450MB/s Without plugging: 220MB/s Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-02-01Btrfs: Add a stripe cache to raid56Chris Mason
The stripe cache allows us to avoid extra read/modify/write cycles by caching the pages we read off the disk. Pages are cached when: * They are read in during a read/modify/write cycle * They are written during a read/modify/write cycle * They are involved in a parity rebuild Pages are not cached if we're doing a full stripe write. We're assuming that a full stripe write won't be followed by another partial stripe write any time soon. This provides a substantial boost in performance for workloads that synchronously modify adjacent offsets in the file, and for the parity rebuild use case in general. The size of the stripe cache isn't tunable (yet) and is set at 1024 entries. Example on flash: dd if=/dev/zero of=/mnt/xxx bs=4K oflag=direct Without the stripe cache -- 2.1MB/s With the stripe cache 21MB/s Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-02-01Btrfs: RAID5 and RAID6David Woodhouse
This builds on David Woodhouse's original Btrfs raid5/6 implementation. The code has changed quite a bit, blame Chris Mason for any bugs. Read/modify/write is done after the higher levels of the filesystem have prepared a given bio. This means the higher layers are not responsible for building full stripes, and they don't need to query for the topology of the extents that may get allocated during delayed allocation runs. It also means different files can easily share the same stripe. But, it does expose us to incorrect parity if we crash or lose power while doing a read/modify/write cycle. This will be addressed in a later commit. Scrub is unable to repair crc errors on raid5/6 chunks. Discard does not work on raid5/6 (yet) The stripe size is fixed at 64KiB per disk. This will be tunable in a later commit. Signed-off-by: Chris Mason <chris.mason@fusionio.com>