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Filesystems often to do compute intensive operation on some metadata. If this operation is repeated many times, it can be very expensive. It would be much nicer if the operation could be performed once before a buffer goes to disk. This adds triggers to jbd2 buffer heads. Just before writing a metadata buffer to the journal, jbd2 will optionally call a commit trigger associated with the buffer. If the journal is aborted, an abort trigger will be called on any dirty buffers as they are dropped from pending transactions. ocfs2 will use this feature. Initially I tried to come up with a more generic trigger that could be used for non-buffer-related events like transaction completion. It doesn't tie nicely, because the information a buffer trigger needs (specific to a journal_head) isn't the same as what a transaction trigger needs (specific to a tranaction_t or perhaps journal_t). So I implemented a buffer set, with the understanding that journal/transaction wide triggers should be implemented separately. There is only one trigger set allowed per buffer. I can't think of any reason to attach more than one set. Contrast this with a journal or transaction in which multiple places may want to watch the entire transaction separately. The trigger sets are considered static allocation from the jbd2 perspective. ocfs2 will just have one trigger set per block type, setting the same set on every bh of the same type. Signed-off-by: Joel Becker <joel.becker@oracle.com> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: <linux-ext4@vger.kernel.org> Signed-off-by: Mark Fasheh <mfasheh@suse.com>
101 lines
2.5 KiB
C
101 lines
2.5 KiB
C
/*
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* include/linux/journal-head.h
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*
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* buffer_head fields for JBD
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*
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* 27 May 2001 Andrew Morton
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* Created - pulled out of fs.h
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*/
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#ifndef JOURNAL_HEAD_H_INCLUDED
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#define JOURNAL_HEAD_H_INCLUDED
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typedef unsigned int tid_t; /* Unique transaction ID */
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typedef struct transaction_s transaction_t; /* Compound transaction type */
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struct buffer_head;
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struct journal_head {
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/*
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* Points back to our buffer_head. [jbd_lock_bh_journal_head()]
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*/
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struct buffer_head *b_bh;
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/*
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* Reference count - see description in journal.c
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* [jbd_lock_bh_journal_head()]
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*/
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int b_jcount;
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/*
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* Journalling list for this buffer [jbd_lock_bh_state()]
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*/
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unsigned b_jlist;
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/*
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* This flag signals the buffer has been modified by
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* the currently running transaction
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* [jbd_lock_bh_state()]
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*/
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unsigned b_modified;
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/*
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* Copy of the buffer data frozen for writing to the log.
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* [jbd_lock_bh_state()]
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*/
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char *b_frozen_data;
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/*
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* Pointer to a saved copy of the buffer containing no uncommitted
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* deallocation references, so that allocations can avoid overwriting
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* uncommitted deletes. [jbd_lock_bh_state()]
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*/
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char *b_committed_data;
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/*
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* Pointer to the compound transaction which owns this buffer's
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* metadata: either the running transaction or the committing
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* transaction (if there is one). Only applies to buffers on a
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* transaction's data or metadata journaling list.
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* [j_list_lock] [jbd_lock_bh_state()]
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*/
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transaction_t *b_transaction;
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/*
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* Pointer to the running compound transaction which is currently
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* modifying the buffer's metadata, if there was already a transaction
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* committing it when the new transaction touched it.
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* [t_list_lock] [jbd_lock_bh_state()]
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*/
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transaction_t *b_next_transaction;
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/*
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* Doubly-linked list of buffers on a transaction's data, metadata or
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* forget queue. [t_list_lock] [jbd_lock_bh_state()]
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*/
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struct journal_head *b_tnext, *b_tprev;
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/*
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* Pointer to the compound transaction against which this buffer
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* is checkpointed. Only dirty buffers can be checkpointed.
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* [j_list_lock]
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*/
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transaction_t *b_cp_transaction;
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/*
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* Doubly-linked list of buffers still remaining to be flushed
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* before an old transaction can be checkpointed.
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* [j_list_lock]
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*/
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struct journal_head *b_cpnext, *b_cpprev;
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/* Trigger type */
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struct jbd2_buffer_trigger_type *b_triggers;
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/* Trigger type for the committing transaction's frozen data */
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struct jbd2_buffer_trigger_type *b_frozen_triggers;
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};
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#endif /* JOURNAL_HEAD_H_INCLUDED */
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