checkpoint.c

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/*
 * linux/fs/checkpoint.c
 * 
 * Written by Stephen C. Tweedie <[e-mail]>, 1999
 *
 * Copyright 1999 Red Hat Software --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Checkpoint routines for the generic filesystem journaling code.  
 * Part of the ext2fs journaling system.  
 *
 * Checkpointing is the process of ensuring that a section of the log is
 * committed fully to disk, so that that portion of the log can be
 * reused.
 */

#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/locks.h>

extern spinlock_t journal_datalist_lock;

/*
 * Unlink a buffer from a transaction. 
 *
 * Called with journal_datalist_lock held.
 */

static inline void __buffer_unlink(struct journal_head *jh)
{
	transaction_t *transaction;

	transaction = jh->b_cp_transaction;
	jh->b_cp_transaction = NULL;

	jh->b_cpnext->b_cpprev = jh->b_cpprev;
	jh->b_cpprev->b_cpnext = jh->b_cpnext;
	if (transaction->t_checkpoint_list == jh)
		transaction->t_checkpoint_list = jh->b_cpnext;
	if (transaction->t_checkpoint_list == jh)
		transaction->t_checkpoint_list = NULL;
}

/*
 * Try to release a checkpointed buffer from its transaction.
 * Returns 1 if we released it.
 * Requires journal_datalist_lock
 */
static int __try_to_free_cp_buf(struct journal_head *jh)
{
	int ret = 0;
	struct buffer_head *bh = jh2bh(jh);

	if (jh->b_jlist == BJ_None && !buffer_locked(bh) && !buffer_dirty(bh)) {
		JBUFFER_TRACE(jh, "remove from checkpoint list");
		__journal_remove_checkpoint(jh);
		__journal_remove_journal_head(bh);
		BUFFER_TRACE(bh, "release");
		/* BUF_LOCKED -> BUF_CLEAN (fwiw) */
		refile_buffer(bh);
		__brelse(bh);
		ret = 1;
	}
	return ret;
}

/*
 * log_wait_for_space: wait until there is space in the journal.
 *
 * Called with the journal already locked, but it will be unlocked if we have
 * to wait for a checkpoint to free up some space in the log.
 */

void log_wait_for_space(journal_t *journal, int nblocks)
{
	while (log_space_left(journal) < nblocks) {
		if (journal->j_flags & JFS_ABORT)
			return;
		unlock_journal(journal);
		down(&journal->j_checkpoint_sem);
		lock_journal(journal);
		
		/* Test again, another process may have checkpointed
		 * while we were waiting for the checkpoint lock */
		if (log_space_left(journal) < nblocks) {
			log_do_checkpoint(journal, nblocks);
		}
		up(&journal->j_checkpoint_sem);
	}
}

/*
 * Clean up a transaction's checkpoint list.  
 *
 * We wait for any pending IO to complete and make sure any clean
 * buffers are removed from the transaction. 
 *
 * Return 1 if we performed any actions which might have destroyed the
 * checkpoint.  (journal_remove_checkpoint() deletes the transaction when
 * the last checkpoint buffer is cleansed)
 *
 * Called with the journal locked.
 * Called with journal_datalist_lock held.
 */
static int __cleanup_transaction(journal_t *journal, transaction_t *transaction)
{
	struct journal_head *jh, *next_jh, *last_jh;
	struct buffer_head *bh;
	int ret = 0;

	assert_spin_locked(&journal_datalist_lock);
	jh = transaction->t_checkpoint_list;
	if (!jh)
		return 0;

	last_jh = jh->b_cpprev;
	next_jh = jh;
	do {
		jh = next_jh;
		bh = jh2bh(jh);
		if (buffer_locked(bh)) {
			atomic_inc(&bh->b_count);
			spin_unlock(&journal_datalist_lock);
			unlock_journal(journal);
			wait_on_buffer(bh);
			/* the journal_head may have gone by now */
			BUFFER_TRACE(bh, "brelse");
			__brelse(bh);
			goto out_return_1;
		}
		
		if (jh->b_transaction != NULL) {
			transaction_t *transaction = jh->b_transaction;
			tid_t tid = transaction->t_tid;

			spin_unlock(&journal_datalist_lock);
			log_start_commit(journal, transaction);
			unlock_journal(journal);
			log_wait_commit(journal, tid);
			goto out_return_1;
		}

		/*
		 * We used to test for (jh->b_list != BUF_CLEAN) here.
		 * But unmap_underlying_metadata() can place buffer onto
		 * BUF_CLEAN. Since refile_buffer() no longer takes buffers
		 * off checkpoint lists, we cope with it here
		 */
		/*
		 * AKPM: I think the buffer_jdirty test is redundant - it
		 * shouldn't have NULL b_transaction?
		 */
		next_jh = jh->b_cpnext;
		if (!buffer_dirty(bh) && !buffer_jdirty(bh)) {
			BUFFER_TRACE(bh, "remove from checkpoint");
			__journal_remove_checkpoint(jh);
			__journal_remove_journal_head(bh);
			refile_buffer(bh);
			__brelse(bh);
			ret = 1;
		}
		
		jh = next_jh;
	} while (jh != last_jh);

	return ret;
out_return_1:
	lock_journal(journal);
	spin_lock(&journal_datalist_lock);
	return 1;
}

#define NR_BATCH	64

static void __flush_batch(struct buffer_head **bhs, int *batch_count)
{
	int i;

	spin_unlock(&journal_datalist_lock);
	ll_rw_block(WRITE, *batch_count, bhs);
	run_task_queue(&tq_disk);
	spin_lock(&journal_datalist_lock);
	for (i = 0; i < *batch_count; i++) {
		struct buffer_head *bh = bhs[i];
		clear_bit(BH_JWrite, &bh->b_state);
		BUFFER_TRACE(bh, "brelse");
		__brelse(bh);
	}
	*batch_count = 0;
}

/*
 * Try to flush one buffer from the checkpoint list to disk.
 *
 * Return 1 if something happened which requires us to abort the current
 * scan of the checkpoint list.  
 *
 * Called with journal_datalist_lock held.
 */
static int __flush_buffer(journal_t *journal, struct journal_head *jh,
			struct buffer_head **bhs, int *batch_count,
			int *drop_count)
{
	struct buffer_head *bh = jh2bh(jh);
	int ret = 0;

	if (buffer_dirty(bh) && !buffer_locked(bh) && jh->b_jlist == BJ_None) {
		J_ASSERT_JH(jh, jh->b_transaction == NULL);
		
		/*
		 * Important: we are about to write the buffer, and
		 * possibly block, while still holding the journal lock.
		 * We cannot afford to let the transaction logic start
		 * messing around with this buffer before we write it to
		 * disk, as that would break recoverability.  
		 */
		BUFFER_TRACE(bh, "queue");
		atomic_inc(&bh->b_count);
		J_ASSERT_BH(bh, !test_bit(BH_JWrite, &bh->b_state));
		set_bit(BH_JWrite, &bh->b_state);
		bhs[*batch_count] = bh;
		(*batch_count)++;
		if (*batch_count == NR_BATCH) {
			__flush_batch(bhs, batch_count);
			ret = 1;
		}
	} else {
		int last_buffer = 0;
		if (jh->b_cpnext == jh) {
			/* We may be about to drop the transaction.  Tell the
			 * caller that the lists have changed.
			 */
			last_buffer = 1;
		}
		if (__try_to_free_cp_buf(jh)) {
			(*drop_count)++;
			ret = last_buffer;
		}
	}
	return ret;
}

	
/*
 * Perform an actual checkpoint.  We don't write out only enough to
 * satisfy the current blocked requests: rather we submit a reasonably
 * sized chunk of the outstanding data to disk at once for
 * efficiency.  log_wait_for_space() will retry if we didn't free enough.
 * 
 * However, we _do_ take into account the amount requested so that once
 * the IO has been queued, we can return as soon as enough of it has
 * completed to disk.  
 *
 * The journal should be locked before calling this function.
 */

/* @@@ `nblocks' is unused.  Should it be used? */
int log_do_checkpoint (journal_t *journal, int nblocks)
{
	transaction_t *transaction, *last_transaction, *next_transaction;
	int result;
	int target;
	int batch_count = 0;
	struct buffer_head *bhs[NR_BATCH];

	jbd_debug(1, "Start checkpoint\n");

	/* 
	 * First thing: if there are any transactions in the log which
	 * don't need checkpointing, just eliminate them from the
	 * journal straight away.  
	 */
	result = cleanup_journal_tail(journal);
	jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
	if (result <= 0)
		return result;

	/*
	 * OK, we need to start writing disk blocks.  Try to free up a
	 * quarter of the log in a single checkpoint if we can.
	 */
	/*
	 * AKPM: check this code.  I had a feeling a while back that it
	 * degenerates into a busy loop at unmount time.
	 */
	target = (journal->j_last - journal->j_first) / 4;

	spin_lock(&journal_datalist_lock);
repeat:
	transaction = journal->j_checkpoint_transactions;
	if (transaction == NULL)
		goto done;
	last_transaction = transaction->t_cpprev;
	next_transaction = transaction;

	do {
		struct journal_head *jh, *last_jh, *next_jh;