Linux-2.6.12-rc2

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / jbd / checkpoint.c

/*
 * linux/fs/checkpoint.c
 * 
 * Written by Stephen C. Tweedie <sct@redhat.com>, 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/time.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>

/*
 * Unlink a buffer from a transaction. 
 *
 * Called with j_list_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 j_list_lock
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
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);
                jbd_unlock_bh_state(bh);
                journal_remove_journal_head(bh);
                BUFFER_TRACE(bh, "release");
                __brelse(bh);
                ret = 1;
        } else {
                jbd_unlock_bh_state(bh);
        }
        return ret;
}

/*
 * __log_wait_for_space: wait until there is space in the journal.
 *
 * Called under j-state_lock *only*.  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;
        assert_spin_locked(&journal->j_state_lock);

        nblocks = jbd_space_needed(journal);
        while (__log_space_left(journal) < nblocks) {
                if (journal->j_flags & JFS_ABORT)
                        return;
                spin_unlock(&journal->j_state_lock);
                down(&journal->j_checkpoint_sem);

                /*
                 * Test again, another process may have checkpointed while we
                 * were waiting for the checkpoint lock
                 */
                spin_lock(&journal->j_state_lock);
                nblocks = jbd_space_needed(journal);
                if (__log_space_left(journal) < nblocks) {
                        spin_unlock(&journal->j_state_lock);
                        log_do_checkpoint(journal);
                        spin_lock(&journal->j_state_lock);
                }
                up(&journal->j_checkpoint_sem);
        }
}

/*
 * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
 * The caller must restart a list walk.  Wait for someone else to run
 * jbd_unlock_bh_state().
 */
static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
{
        get_bh(bh);
        spin_unlock(&journal->j_list_lock);
        jbd_lock_bh_state(bh);
        jbd_unlock_bh_state(bh);
        put_bh(bh);
}

/*
 * 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 j_list_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->j_list_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->j_list_lock);
                        wait_on_buffer(bh);
                        /* the journal_head may have gone by now */
                        BUFFER_TRACE(bh, "brelse");
                        __brelse(bh);
                        goto out_return_1;
                }

                /*
                 * This is foul
                 */
                if (!jbd_trylock_bh_state(bh)) {
                        jbd_sync_bh(journal, bh);
                        goto out_return_1;
                }

                if (jh->b_transaction != NULL) {
                        transaction_t *t = jh->b_transaction;
                        tid_t tid = t->t_tid;

                        spin_unlock(&journal->j_list_lock);
                        jbd_unlock_bh_state(bh);
                        log_start_commit(journal, tid);
                        log_wait_commit(journal, tid);
                        goto out_return_1;
                }

                /*
                 * AKPM: I think the buffer_jbddirty test is redundant - it
                 * shouldn't have NULL b_transaction?
                 */
                next_jh = jh->b_cpnext;
                if (!buffer_dirty(bh) && !buffer_jbddirty(bh)) {
                        BUFFER_TRACE(bh, "remove from checkpoint");
                        __journal_remove_checkpoint(jh);
                        jbd_unlock_bh_state(bh);
                        journal_remove_journal_head(bh);
                        __brelse(bh);
                        ret = 1;
                } else {
                        jbd_unlock_bh_state(bh);
                }
                jh = next_jh;
        } while (jh != last_jh);

        return ret;
out_return_1:
        spin_lock(&journal->j_list_lock);
        return 1;
}

#define NR_BATCH        64

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

        spin_unlock(&journal->j_list_lock);
        ll_rw_block(WRITE, *batch_count, bhs);
        spin_lock(&journal->j_list_lock);
        for (i = 0; i < *batch_count; i++) {
                struct buffer_head *bh = bhs[i];
                clear_buffer_jwrite(bh);
                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 j_list_lock held.
 * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
 */
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");
                get_bh(bh);
                J_ASSERT_BH(bh, !buffer_jwrite(bh));
                set_buffer_jwrite(bh);
                bhs[*batch_count] = bh;
                jbd_unlock_bh_state(bh);
                (*batch_count)++;
                if (*batch_count == NR_BATCH) {
                        __flush_batch(journal, 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.
 */
int log_do_checkpoint(journal_t *journal)
{
        int result;
        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.
         */
        spin_lock(&journal->j_list_lock);
        while (journal->j_checkpoint_transactions) {
                transaction_t *transaction;
                struct journal_head *jh, *last_jh, *next_jh;
                int drop_count = 0;
                int cleanup_ret, retry = 0;
                tid_t this_tid;

                transaction = journal->j_checkpoint_transactions;
                this_tid = transaction->t_tid;
                jh = transaction->t_checkpoint_list;
                last_jh = jh->b_cpprev;
                next_jh = jh;
                do {
                        struct buffer_head *bh;

                        jh = next_jh;
                        next_jh = jh->b_cpnext;
                        bh = jh2bh(jh);
                        if (!jbd_trylock_bh_state(bh)) {
                                jbd_sync_bh(journal, bh);
                                spin_lock(&journal->j_list_lock);
                                retry = 1;
                                break;
                        }
                        retry = __flush_buffer(journal, jh, bhs, &batch_count, &drop_count);
                        if (cond_resched_lock(&journal->j_list_lock)) {
                                retry = 1;
                                break;
                        }
                } while (jh != last_jh && !retry);

                if (batch_count)
                        __flush_batch(journal, bhs, &batch_count);

                /*
                 * If someone cleaned up this transaction while we slept, we're
                 * done
                 */
                if (journal->j_checkpoint_transactions != transaction)
                        break;
                if (retry)
                        continue;
                /*
                 * Maybe it's a new transaction, but it fell at the same
                 * address
                 */
                if (transaction->t_tid != this_tid)
                        continue;
                /*
                 * We have walked the whole transaction list without
                 * finding anything to write to disk.  We had better be
                 * able to make some progress or we are in trouble. 
                 */
                cleanup_ret = __cleanup_transaction(journal, transaction);
                J_ASSERT(drop_count != 0 || cleanup_ret != 0);
                if (journal->j_checkpoint_transactions != transaction)
                        break;
        }
        spin_unlock(&journal->j_list_lock);
        result = cleanup_journal_tail(journal);
        if (result < 0)
                return result;

        return 0;
}

/*
 * Check the list of checkpoint transactions for the journal to see if
 * we have already got rid of any since the last update of the log tail
 * in the journal superblock.  If so, we can instantly roll the
 * superblock forward to remove those transactions from the log.
 * 
 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 * 
 * Called with the journal lock held.
 *
 * This is the only part of the journaling code which really needs to be
 * aware of transaction aborts.  Checkpointing involves writing to the
 * main filesystem area rather than to the journal, so it can proceed
 * even in abort state, but we must not update the journal superblock if
 * we have an abort error outstanding.
 */

int cleanup_journal_tail(journal_t *journal)
{
        transaction_t * transaction;
        tid_t           first_tid;
        unsigned long   blocknr, freed;

        /* OK, work out the oldest transaction remaining in the log, and
         * the log block it starts at. 
         * 
         * If the log is now empty, we need to work out which is the
         * next transaction ID we will write, and where it will
         * start. */

        spin_lock(&journal->j_state_lock);
        spin_lock(&journal->j_list_lock);
        transaction = journal->j_checkpoint_transactions;
        if (transaction) {
                first_tid = transaction->t_tid;
                blocknr = transaction->t_log_start;
        } else if ((transaction = journal->j_committing_transaction) != NULL) {
                first_tid = transaction->t_tid;
                blocknr = transaction->t_log_start;
        } else if ((transaction = journal->j_running_transaction) != NULL) {
                first_tid = transaction->t_tid;
                blocknr = journal->j_head;
        } else {
                first_tid = journal->j_transaction_sequence;
                blocknr = journal->j_head;
        }
        spin_unlock(&journal->j_list_lock);
        J_ASSERT(blocknr != 0);

        /* If the oldest pinned transaction is at the tail of the log
           already then there's not much we can do right now. */
        if (journal->j_tail_sequence == first_tid) {
                spin_unlock(&journal->j_state_lock);
                return 1;
        }

        /* OK, update the superblock to recover the freed space.
         * Physical blocks come first: have we wrapped beyond the end of
         * the log?  */
        freed = blocknr - journal->j_tail;
        if (blocknr < journal->j_tail)
                freed = freed + journal->j_last - journal->j_first;

        jbd_debug(1,
                  "Cleaning journal tail from %d to %d (offset %lu), "
                  "freeing %lu\n",
                  journal->j_tail_sequence, first_tid, blocknr, freed);

        journal->j_free += freed;
        journal->j_tail_sequence = first_tid;
        journal->j_tail = blocknr;
        spin_unlock(&journal->j_state_lock);
        if (!(journal->j_flags & JFS_ABORT))
                journal_update_superblock(journal, 1);
        return 0;
}


/* Checkpoint list management */

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of bufers reaped (for debug)
 */

int __journal_clean_checkpoint_list(journal_t *journal)
{
        transaction_t *transaction, *last_transaction, *next_transaction;
        int ret = 0;

        transaction = journal->j_checkpoint_transactions;
        if (transaction == 0)
                goto out;

        last_transaction = transaction->t_cpprev;
        next_transaction = transaction;
        do {
                struct journal_head *jh;

                transaction = next_transaction;
                next_transaction = transaction->t_cpnext;
                jh = transaction->t_checkpoint_list;
                if (jh) {
                        struct journal_head *last_jh = jh->b_cpprev;
                        struct journal_head *next_jh = jh;

                        do {
                                jh = next_jh;
                                next_jh = jh->b_cpnext;
                                /* Use trylock because of the ranknig */
                                if (jbd_trylock_bh_state(jh2bh(jh)))
                                        ret += __try_to_free_cp_buf(jh);
                                /*
                                 * This function only frees up some memory
                                 * if possible so we dont have an obligation
                                 * to finish processing. Bail out if preemption
                                 * requested:
                                 */
                                if (need_resched())
                                        goto out;
                        } while (jh != last_jh);
                }
        } while (transaction != last_transaction);
out:
        return ret;
}

/* 
 * journal_remove_checkpoint: called after a buffer has been committed
 * to disk (either by being write-back flushed to disk, or being
 * committed to the log).
 *
 * We cannot safely clean a transaction out of the log until all of the
 * buffer updates committed in that transaction have safely been stored
 * elsewhere on disk.  To achieve this, all of the buffers in a
 * transaction need to be maintained on the transaction's checkpoint
 * list until they have been rewritten, at which point this function is
 * called to remove the buffer from the existing transaction's
 * checkpoint list.  
 *
 * This function is called with the journal locked.
 * This function is called with j_list_lock held.
 */

void __journal_remove_checkpoint(struct journal_head *jh)
{
        transaction_t *transaction;
        journal_t *journal;

        JBUFFER_TRACE(jh, "entry");

        if ((transaction = jh->b_cp_transaction) == NULL) {
                JBUFFER_TRACE(jh, "not on transaction");
                goto out;
        }
        journal = transaction->t_journal;

        __buffer_unlink(jh);

        if (transaction->t_checkpoint_list != NULL)
                goto out;
        JBUFFER_TRACE(jh, "transaction has no more buffers");

        /*
         * There is one special case to worry about: if we have just pulled the
         * buffer off a committing transaction's forget list, then even if the
         * checkpoint list is empty, the transaction obviously cannot be
         * dropped!
         *
         * The locking here around j_committing_transaction is a bit sleazy.
         * See the comment at the end of journal_commit_transaction().
         */
        if (transaction == journal->j_committing_transaction) {
                JBUFFER_TRACE(jh, "belongs to committing transaction");
                goto out;
        }

        /* OK, that was the last buffer for the transaction: we can now
           safely remove this transaction from the log */

        __journal_drop_transaction(journal, transaction);

        /* Just in case anybody was waiting for more transactions to be
           checkpointed... */
        wake_up(&journal->j_wait_logspace);
out:
        JBUFFER_TRACE(jh, "exit");
}

/*
 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 * list so that we know when it is safe to clean the transaction out of
 * the log.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */
void __journal_insert_checkpoint(struct journal_head *jh, 
                               transaction_t *transaction)
{
        JBUFFER_TRACE(jh, "entry");
        J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
        J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

        jh->b_cp_transaction = transaction;

        if (!transaction->t_checkpoint_list) {
                jh->b_cpnext = jh->b_cpprev = jh;
        } else {
                jh->b_cpnext = transaction->t_checkpoint_list;
                jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
                jh->b_cpprev->b_cpnext = jh;
                jh->b_cpnext->b_cpprev = jh;
        }
        transaction->t_checkpoint_list = jh;
}

/*
 * We've finished with this transaction structure: adios...
 * 
 * The transaction must have no links except for the checkpoint by this
 * point.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */

void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
        assert_spin_locked(&journal->j_list_lock);
        if (transaction->t_cpnext) {
                transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
                transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
                if (journal->j_checkpoint_transactions == transaction)
                        journal->j_checkpoint_transactions =
                                transaction->t_cpnext;
                if (journal->j_checkpoint_transactions == transaction)
                        journal->j_checkpoint_transactions = NULL;
        }

        J_ASSERT(transaction->t_state == T_FINISHED);
        J_ASSERT(transaction->t_buffers == NULL);
        J_ASSERT(transaction->t_sync_datalist == NULL);
        J_ASSERT(transaction->t_forget == NULL);
        J_ASSERT(transaction->t_iobuf_list == NULL);
        J_ASSERT(transaction->t_shadow_list == NULL);
        J_ASSERT(transaction->t_log_list == NULL);
        J_ASSERT(transaction->t_checkpoint_list == NULL);
        J_ASSERT(transaction->t_updates == 0);
        J_ASSERT(journal->j_committing_transaction != transaction);
        J_ASSERT(journal->j_running_transaction != transaction);

        jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
        kfree(transaction);
}