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/*

 * 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/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;

                int drop_count = 0;

                int cleanup_ret, retry = 0;

                transaction = next_transaction;

                next_transaction = transaction->t_cpnext;

                jh = transaction->t_checkpoint_list;

                last_jh = jh->b_cpprev;

                next_jh = jh;

                do {

                        jh = next_jh;

                        next_jh = jh->b_cpnext;

                        retry = __flush_buffer(journal, jh, bhs, &batch_count,

                                                &drop_count);

                } while (jh != last_jh && !retry);

                if (batch_count) {

                        __flush_batch(bhs, &batch_count);

                        goto repeat;

                }

                if (retry)

                        goto repeat;

                /*

                 * 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);

                goto repeat;    /* __cleanup may have dropped lock */

        } while (transaction != last_transaction);

done:

        spin_unlock(&journal_datalist_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. */

        /* j_checkpoint_transactions needs locking */

        spin_lock(&journal_datalist_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_datalist_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)

                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;

        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 journal_datalist_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;

                                ret += __try_to_free_cp_buf(jh);

                        } 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 journal_datalist_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! */

        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");

}

void journal_remove_checkpoint(struct journal_head *jh)

{

        spin_lock(&journal_datalist_lock);

        __journal_remove_checkpoint(jh);

        spin_unlock(&journal_datalist_lock);

}

/*

 * 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 journal_datalist_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_jdirty(jh2bh(jh)));

        J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

        assert_spin_locked(&journal_datalist_lock);

        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;

}

void journal_insert_checkpoint(struct journal_head *jh,

                               transaction_t *transaction)

{

        spin_lock(&journal_datalist_lock);

        __journal_insert_checkpoint(jh, transaction);

        spin_unlock(&journal_datalist_lock);

}

/*

 * 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 journal_datalist_lock held.

 */

void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)

{

        assert_spin_locked(&journal_datalist_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_ilist == NULL);

        J_ASSERT (transaction->t_buffers == NULL);

        J_ASSERT (transaction->t_sync_datalist == NULL);

        J_ASSERT (transaction->t_async_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 (list_empty(&transaction->t_jcb));

        J_ASSERT (transaction->t_journal->j_committing_transaction !=

                                        transaction);

        jbd_debug (1, "Dropping transaction %d, all done\n",

                   transaction->t_tid);

        kfree (transaction);

}