@@ -10,27 +10,27 @@ Details
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The journalling layer is easy to use. You need to first of all create a
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journal_t data structure. There are two calls to do this dependent on
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how you decide to allocate the physical media on which the journal
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- resides. The :c:func: ` jbd2_journal_init_inode ` call is for journals stored in
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- filesystem inodes, or the :c:func: ` jbd2_journal_init_dev ` call can be used
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+ resides. The jbd2_journal_init_inode() call is for journals stored in
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+ filesystem inodes, or the jbd2_journal_init_dev() call can be used
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for journal stored on a raw device (in a continuous range of blocks). A
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journal_t is a typedef for a struct pointer, so when you are finally
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- finished make sure you call :c:func: ` jbd2_journal_destroy ` on it to free up
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+ finished make sure you call jbd2_journal_destroy() on it to free up
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any used kernel memory.
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Once you have got your journal_t object you need to 'mount' or load the
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journal file. The journalling layer expects the space for the journal
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was already allocated and initialized properly by the userspace tools.
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- When loading the journal you must call :c:func: ` jbd2_journal_load ` to process
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+ When loading the journal you must call jbd2_journal_load() to process
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journal contents. If the client file system detects the journal contents
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does not need to be processed (or even need not have valid contents), it
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- may call :c:func: ` jbd2_journal_wipe ` to clear the journal contents before
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- calling :c:func: ` jbd2_journal_load ` .
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+ may call jbd2_journal_wipe() to clear the journal contents before
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+ calling jbd2_journal_load() .
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Note that jbd2_journal_wipe(..,0) calls
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- :c:func: ` jbd2_journal_skip_recovery ` for you if it detects any outstanding
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- transactions in the journal and similarly :c:func: ` jbd2_journal_load ` will
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- call :c:func: ` jbd2_journal_recover ` if necessary. I would advise reading
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- :c:func: ` ext4_load_journal ` in fs/ext4/super.c for examples on this stage.
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+ jbd2_journal_skip_recovery() for you if it detects any outstanding
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+ transactions in the journal and similarly jbd2_journal_load() will
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+ call jbd2_journal_recover() if necessary. I would advise reading
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+ ext4_load_journal() in fs/ext4/super.c for examples on this stage.
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Now you can go ahead and start modifying the underlying filesystem.
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Almost.
@@ -39,57 +39,57 @@ You still need to actually journal your filesystem changes, this is done
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by wrapping them into transactions. Additionally you also need to wrap
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the modification of each of the buffers with calls to the journal layer,
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so it knows what the modifications you are actually making are. To do
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- this use :c:func: ` jbd2_journal_start ` which returns a transaction handle.
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+ this use jbd2_journal_start() which returns a transaction handle.
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- :c:func: ` jbd2_journal_start ` and its counterpart :c:func: ` jbd2_journal_stop ` ,
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+ jbd2_journal_start() and its counterpart jbd2_journal_stop() ,
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which indicates the end of a transaction are nestable calls, so you can
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reenter a transaction if necessary, but remember you must call
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- :c:func: ` jbd2_journal_stop ` the same number of times as
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- :c:func: ` jbd2_journal_start ` before the transaction is completed (or more
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+ jbd2_journal_stop() the same number of times as
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+ jbd2_journal_start() before the transaction is completed (or more
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accurately leaves the update phase). Ext4/VFS makes use of this feature to
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simplify handling of inode dirtying, quota support, etc.
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Inside each transaction you need to wrap the modifications to the
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individual buffers (blocks). Before you start to modify a buffer you
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- need to call :c:func: ` jbd2_journal_get_create_access() ` /
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- :c:func: ` jbd2_journal_get_write_access() ` /
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- :c:func: ` jbd2_journal_get_undo_access() ` as appropriate, this allows the
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+ need to call jbd2_journal_get_create_access() /
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+ jbd2_journal_get_write_access() /
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+ jbd2_journal_get_undo_access() as appropriate, this allows the
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journalling layer to copy the unmodified
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data if it needs to. After all the buffer may be part of a previously
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uncommitted transaction. At this point you are at last ready to modify a
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buffer, and once you are have done so you need to call
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- :c:func: ` jbd2_journal_dirty_metadata ` . Or if you've asked for access to a
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+ jbd2_journal_dirty_metadata() . Or if you've asked for access to a
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buffer you now know is now longer required to be pushed back on the
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- device you can call :c:func: ` jbd2_journal_forget ` in much the same way as you
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- might have used :c:func: ` bforget ` in the past.
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+ device you can call jbd2_journal_forget() in much the same way as you
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+ might have used bforget() in the past.
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- A :c:func: ` jbd2_journal_flush ` may be called at any time to commit and
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+ A jbd2_journal_flush() may be called at any time to commit and
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checkpoint all your transactions.
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- Then at umount time , in your :c:func: ` put_super ` you can then call
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- :c:func: ` jbd2_journal_destroy ` to clean up your in-core journal object.
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+ Then at umount time , in your put_super() you can then call
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+ jbd2_journal_destroy() to clean up your in-core journal object.
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Unfortunately there a couple of ways the journal layer can cause a
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deadlock. The first thing to note is that each task can only have a
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single outstanding transaction at any one time, remember nothing commits
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- until the outermost :c:func: ` jbd2_journal_stop ` . This means you must complete
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+ until the outermost jbd2_journal_stop() . This means you must complete
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the transaction at the end of each file/inode/address etc. operation you
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perform, so that the journalling system isn't re-entered on another
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journal. Since transactions can't be nested/batched across differing
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journals, and another filesystem other than yours (say ext4) may be
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modified in a later syscall.
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- The second case to bear in mind is that :c:func: ` jbd2_journal_start ` can block
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+ The second case to bear in mind is that jbd2_journal_start() can block
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if there isn't enough space in the journal for your transaction (based
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on the passed nblocks param) - when it blocks it merely(!) needs to wait
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for transactions to complete and be committed from other tasks, so
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- essentially we are waiting for :c:func: ` jbd2_journal_stop ` . So to avoid
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- deadlocks you must treat :c:func: ` jbd2_journal_start ` /
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- :c:func: ` jbd2_journal_stop ` as if they were semaphores and include them in
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+ essentially we are waiting for jbd2_journal_stop() . So to avoid
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+ deadlocks you must treat jbd2_journal_start() /
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+ jbd2_journal_stop() as if they were semaphores and include them in
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your semaphore ordering rules to prevent
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- deadlocks. Note that :c:func: ` jbd2_journal_extend ` has similar blocking
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- behaviour to :c:func: ` jbd2_journal_start ` so you can deadlock here just as
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- easily as on :c:func: ` jbd2_journal_start ` .
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+ deadlocks. Note that jbd2_journal_extend() has similar blocking
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+ behaviour to jbd2_journal_start() so you can deadlock here just as
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+ easily as on jbd2_journal_start() .
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Try to reserve the right number of blocks the first time. ;-). This will
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be the maximum number of blocks you are going to touch in this
@@ -116,8 +116,8 @@ called after each transaction commit. You can also use
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that need processing when the transaction commits.
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JBD2 also provides a way to block all transaction updates via
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- :c:func: ` jbd2_journal_lock_updates() ` /
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- :c:func: ` jbd2_journal_unlock_updates() ` . Ext4 uses this when it wants a
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+ jbd2_journal_lock_updates() /
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+ jbd2_journal_unlock_updates(). Ext4 uses this when it wants a
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window with a clean and stable fs for a moment. E.g.
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