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/*

 * linux/fs/revoke.c

 *

 * Written by Stephen C. Tweedie <sct@redhat.com>, 2000

 *

 * Copyright 2000 Red Hat corp --- 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.

 *

 * Journal revoke routines for the generic filesystem journaling code;

 * part of the ext2fs journaling system.

 *

 * Revoke is the mechanism used to prevent old log records for deleted

 * metadata from being replayed on top of newer data using the same

 * blocks.  The revoke mechanism is used in two separate places:

 *

 * + Commit: during commit we write the entire list of the current

 *   transaction's revoked blocks to the journal

 *

 * + Recovery: during recovery we record the transaction ID of all

 *   revoked blocks.  If there are multiple revoke records in the log

 *   for a single block, only the last one counts, and if there is a log

 *   entry for a block beyond the last revoke, then that log entry still

 *   gets replayed.

 *

 * We can get interactions between revokes and new log data within a

 * single transaction:

 *

 * Block is revoked and then journaled:

 *   The desired end result is the journaling of the new block, so we

 *   cancel the revoke before the transaction commits.

 *

 * Block is journaled and then revoked:

 *   The revoke must take precedence over the write of the block, so we

 *   need either to cancel the journal entry or to write the revoke

 *   later in the log than the log block.  In this case, we choose the

 *   latter: journaling a block cancels any revoke record for that block

 *   in the current transaction, so any revoke for that block in the

 *   transaction must have happened after the block was journaled and so

 *   the revoke must take precedence.

 *

 * Block is revoked and then written as data:

 *   The data write is allowed to succeed, but the revoke is _not_

 *   cancelled.  We still need to prevent old log records from

 *   overwriting the new data.  We don't even need to clear the revoke

 *   bit here.

 *

 * Revoke information on buffers is a tri-state value:

 *

 * RevokeValid clear:   no cached revoke status, need to look it up

 * RevokeValid set, Revoked clear:

 *                      buffer has not been revoked, and cancel_revoke

 *                      need do nothing.

 * RevokeValid set, Revoked set:

 *                      buffer has been revoked.

 */

#ifndef __KERNEL__

#include "jfs_user.h"

#else

#include <linux/sched.h>

#include <linux/fs.h>

#include <linux/jbd.h>

#include <linux/errno.h>

#include <linux/slab.h>

#include <linux/locks.h>

#include <linux/list.h>

#include <linux/smp_lock.h>

#include <linux/init.h>

#endif

static kmem_cache_t *revoke_record_cache;

static kmem_cache_t *revoke_table_cache;

/* Each revoke record represents one single revoked block.  During

   journal replay, this involves recording the transaction ID of the

   last transaction to revoke this block. */

struct jbd_revoke_record_s

{

        struct list_head  hash;

        tid_t             sequence;     /* Used for recovery only */

        unsigned long     blocknr;

};

/* The revoke table is just a simple hash table of revoke records. */

struct jbd_revoke_table_s

{

        /* It is conceivable that we might want a larger hash table

         * for recovery.  Must be a power of two. */

        int               hash_size;

        int               hash_shift;

        struct list_head *hash_table;

};

#ifdef __KERNEL__

static void write_one_revoke_record(journal_t *, transaction_t *,

                                    struct journal_head **, int *,

                                    struct jbd_revoke_record_s *);

static void flush_descriptor(journal_t *, struct journal_head *, int);

#endif

/* Utility functions to maintain the revoke table */

/* Borrowed from buffer.c: this is a tried and tested block hash function */

static inline int hash(journal_t *journal, unsigned long block)

{

        struct jbd_revoke_table_s *table = journal->j_revoke;

        int hash_shift = table->hash_shift;

        return ((block << (hash_shift - 6)) ^

                (block >> 13) ^

                (block << (hash_shift - 12))) & (table->hash_size - 1);

}

int insert_revoke_hash(journal_t *journal, unsigned long blocknr, tid_t seq)

{

        struct list_head *hash_list;

        struct jbd_revoke_record_s *record;

repeat:

        record = kmem_cache_alloc(revoke_record_cache, GFP_NOFS);

        if (!record)

                goto oom;

        record->sequence = seq;

        record->blocknr = blocknr;

        hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];

        list_add(&record->hash, hash_list);

        return 0;

oom:

        if (!journal_oom_retry)

                return -ENOMEM;

        jbd_debug(1, "ENOMEM in %s, retrying.\n", __FUNCTION__);

        yield();

        goto repeat;

}

/* Find a revoke record in the journal's hash table. */

static struct jbd_revoke_record_s *find_revoke_record(journal_t *journal,

                                                      unsigned long blocknr)

{

        struct list_head *hash_list;

        struct jbd_revoke_record_s *record;

        hash_list = &journal->j_revoke->hash_table[hash(journal, blocknr)];

        record = (struct jbd_revoke_record_s *) hash_list->next;

        while (&(record->hash) != hash_list) {

                if (record->blocknr == blocknr)

                        return record;

                record = (struct jbd_revoke_record_s *) record->hash.next;

        }

        return NULL;

}

int __init journal_init_revoke_caches(void)

{

        revoke_record_cache = kmem_cache_create("revoke_record",

                                           sizeof(struct jbd_revoke_record_s),

                                           0, SLAB_HWCACHE_ALIGN, NULL, NULL);

        if (revoke_record_cache == 0)

                return -ENOMEM;

        revoke_table_cache = kmem_cache_create("revoke_table",

                                           sizeof(struct jbd_revoke_table_s),

                                           0, 0, NULL, NULL);

        if (revoke_table_cache == 0) {

                kmem_cache_destroy(revoke_record_cache);

                revoke_record_cache = NULL;

                return -ENOMEM;

        }

        return 0;

}

void journal_destroy_revoke_caches(void)

{

        kmem_cache_destroy(revoke_record_cache);

        revoke_record_cache = 0;

        kmem_cache_destroy(revoke_table_cache);

        revoke_table_cache = 0;

}

/* Initialise the revoke table for a given journal to a given size. */

int journal_init_revoke(journal_t *journal, int hash_size)

{

        int shift, tmp;

        J_ASSERT (journal->j_revoke == NULL);

        journal->j_revoke = kmem_cache_alloc(revoke_table_cache, GFP_KERNEL);

        if (!journal->j_revoke)

                return -ENOMEM;

        /* Check that the hash_size is a power of two */

        J_ASSERT ((hash_size & (hash_size-1)) == 0);

        journal->j_revoke->hash_size = hash_size;

        shift = 0;

        tmp = hash_size;

        while((tmp >>= 1UL) != 0UL)

                shift++;

        journal->j_revoke->hash_shift = shift;

        journal->j_revoke->hash_table =

                kmalloc(hash_size * sizeof(struct list_head), GFP_KERNEL);

        if (!journal->j_revoke->hash_table) {

                kmem_cache_free(revoke_table_cache, journal->j_revoke);

                journal->j_revoke = NULL;

                return -ENOMEM;

        }

        for (tmp = 0; tmp < hash_size; tmp++)

                INIT_LIST_HEAD(&journal->j_revoke->hash_table[tmp]);

        return 0;

}

/* Destoy a journal's revoke table.  The table must already be empty! */

void journal_destroy_revoke(journal_t *journal)

{

        struct jbd_revoke_table_s *table;

        struct list_head *hash_list;

        int i;

        table = journal->j_revoke;

        if (!table)

                return;

        for (i=0; i<table->hash_size; i++) {

                hash_list = &table->hash_table[i];

                J_ASSERT (list_empty(hash_list));

        }

        kfree(table->hash_table);

        kmem_cache_free(revoke_table_cache, table);

        journal->j_revoke = NULL;

}

#ifdef __KERNEL__

/*

 * journal_revoke: revoke a given buffer_head from the journal.  This

 * prevents the block from being replayed during recovery if we take a

 * crash after this current transaction commits.  Any subsequent

 * metadata writes of the buffer in this transaction cancel the

 * revoke.

 *

 * Note that this call may block --- it is up to the caller to make

 * sure that there are no further calls to journal_write_metadata

 * before the revoke is complete.  In ext3, this implies calling the

 * revoke before clearing the block bitmap when we are deleting

 * metadata.

 *

 * Revoke performs a journal_forget on any buffer_head passed in as a

 * parameter, but does _not_ forget the buffer_head if the bh was only

 * found implicitly.

 *

 * bh_in may not be a journalled buffer - it may have come off

 * the hash tables without an attached journal_head.

 *

 * If bh_in is non-zero, journal_revoke() will decrement its b_count

 * by one.

 */

int journal_revoke(handle_t *handle, unsigned long blocknr,

                   struct buffer_head *bh_in)

{

        struct buffer_head *bh = NULL;

        journal_t *journal;

        kdev_t dev;

        int err;

        if (bh_in)

                BUFFER_TRACE(bh_in, "enter");

        journal = handle->h_transaction->t_journal;

        if (!journal_set_features(journal, 0, 0, JFS_FEATURE_INCOMPAT_REVOKE)){

                J_ASSERT (!"Cannot set revoke feature!");

                return -EINVAL;

        }

        dev = journal->j_fs_dev;

        bh = bh_in;

        if (!bh) {

                bh = get_hash_table(dev, blocknr, journal->j_blocksize);

                if (bh)

                        BUFFER_TRACE(bh, "found on hash");

        }

#ifdef JBD_EXPENSIVE_CHECKING

        else {

                struct buffer_head *bh2;

                /* If there is a different buffer_head lying around in

                 * memory anywhere... */

                bh2 = get_hash_table(dev, blocknr, journal->j_blocksize);

                if (bh2) {

                        /* ... and it has RevokeValid status... */

                        if ((bh2 != bh) &&

                            test_bit(BH_RevokeValid, &bh2->b_state))

                                /* ...then it better be revoked too,

                                 * since it's illegal to create a revoke

                                 * record against a buffer_head which is

                                 * not marked revoked --- that would

                                 * risk missing a subsequent revoke

                                 * cancel. */

                                J_ASSERT_BH(bh2, test_bit(BH_Revoked, &

                                                          bh2->b_state));

                        __brelse(bh2);

                }

        }

#endif

        /* We really ought not ever to revoke twice in a row without

           first having the revoke cancelled: it's illegal to free a

           block twice without allocating it in between! */

        if (bh) {

                J_ASSERT_BH(bh, !test_bit(BH_Revoked, &bh->b_state));

                set_bit(BH_Revoked, &bh->b_state);

                set_bit(BH_RevokeValid, &bh->b_state);

                if (bh_in) {

                        BUFFER_TRACE(bh_in, "call journal_forget");

                        journal_forget(handle, bh_in);

                } else {

                        BUFFER_TRACE(bh, "call brelse");

                        __brelse(bh);

                }

        }

        lock_journal(journal);

        jbd_debug(2, "insert revoke for block %lu, bh_in=%p\n", blocknr, bh_in);

        err = insert_revoke_hash(journal, blocknr,

                                handle->h_transaction->t_tid);

        unlock_journal(journal);

        BUFFER_TRACE(bh_in, "exit");

        return err;

}

/*

 * Cancel an outstanding revoke.  For use only internally by the

 * journaling code (called from journal_get_write_access).

 *

 * We trust the BH_Revoked bit on the buffer if the buffer is already

 * being journaled: if there is no revoke pending on the buffer, then we

 * don't do anything here.

 *

 * This would break if it were possible for a buffer to be revoked and

 * discarded, and then reallocated within the same transaction.  In such

 * a case we would have lost the revoked bit, but when we arrived here

 * the second time we would still have a pending revoke to cancel.  So,

 * do not trust the Revoked bit on buffers unless RevokeValid is also

 * set.

 *

 * The caller must have the journal locked.

 */

int journal_cancel_revoke(handle_t *handle, struct journal_head *jh)

{

        struct jbd_revoke_record_s *record;

        journal_t *journal = handle->h_transaction->t_journal;

        int need_cancel;

        int did_revoke = 0;      /* akpm: debug */

        struct buffer_head *bh = jh2bh(jh);

        jbd_debug(4, "journal_head %p, cancelling revoke\n", jh);

        /* Is the existing Revoke bit valid?  If so, we trust it, and

         * only perform the full cancel if the revoke bit is set.  If

         * not, we can't trust the revoke bit, and we need to do the

         * full search for a revoke record. */

        if (test_and_set_bit(BH_RevokeValid, &bh->b_state))

                need_cancel = (test_and_clear_bit(BH_Revoked, &bh->b_state));

        else {

                need_cancel = 1;

                clear_bit(BH_Revoked, &bh->b_state);

        }

        if (need_cancel) {

                record = find_revoke_record(journal, bh->b_blocknr);

                if (record) {

                        jbd_debug(4, "cancelled existing revoke on "

                                  "blocknr %lu\n", bh->b_blocknr);

                        list_del(&record->hash);

                        kmem_cache_free(revoke_record_cache, record);

                        did_revoke = 1;

                }

        }

#ifdef JBD_EXPENSIVE_CHECKING

        /* There better not be one left behind by now! */

        record = find_revoke_record(journal, bh->b_blocknr);

        J_ASSERT_JH(jh, record == NULL);

#endif

        /* Finally, have we just cleared revoke on an unhashed

         * buffer_head?  If so, we'd better make sure we clear the

         * revoked status on any hashed alias too, otherwise the revoke

         * state machine will get very upset later on. */

        if (need_cancel && !bh->b_pprev) {

                struct buffer_head *bh2;

                bh2 = get_hash_table(bh->b_dev, bh->b_blocknr, bh->b_size);

                if (bh2) {

                        clear_bit(BH_Revoked, &bh2->b_state);

                        __brelse(bh2);

                }

        }

        return did_revoke;

}

/*

 * Write revoke records to the journal for all entries in the current

 * revoke hash, deleting the entries as we go.

 *

 * Called with the journal lock held.

 */

void journal_write_revoke_records(journal_t *journal,

                                  transaction_t *transaction)

{

        struct journal_head *descriptor;

        struct jbd_revoke_record_s *record;

        struct jbd_revoke_table_s *revoke;

        struct list_head *hash_list;

        int i, offset, count;

        descriptor = NULL;

        offset = 0;

        count = 0;

        revoke = journal->j_revoke;

        for (i = 0; i < revoke->hash_size; i++) {

                hash_list = &revoke->hash_table[i];

                while (!list_empty(hash_list)) {

                        record = (struct jbd_revoke_record_s *)

                                hash_list->next;

                        write_one_revoke_record(journal, transaction,

                                                &descriptor, &offset,

                                                record);

                        count++;

                        list_del(&record->hash);

                        kmem_cache_free(revoke_record_cache, record);

                }

        }

        if (descriptor)

                flush_descriptor(journal, descriptor, offset);

        jbd_debug(1, "Wrote %d revoke records\n", count);

}

/*

 * Write out one revoke record.  We need to create a new descriptor

 * block if the old one is full or if we have not already created one.

 */

static void write_one_revoke_record(journal_t *journal,

                                    transaction_t *transaction,

                                    struct journal_head **descriptorp,

                                    int *offsetp,

                                    struct jbd_revoke_record_s *record)

{

        struct journal_head *descriptor;

        int offset;

        journal_header_t *header;

        /* If we are already aborting, this all becomes a noop.  We

           still need to go round the loop in

           journal_write_revoke_records in order to free all of the

           revoke records: only the IO to the journal is omitted. */

        if (is_journal_aborted(journal))

                return;

        descriptor = *descriptorp;

        offset = *offsetp;

        /* Make sure we have a descriptor with space left for the record */

        if (descriptor) {

                if (offset == journal->j_blocksize) {

                        flush_descriptor(journal, descriptor, offset);

                        descriptor = NULL;

                }

        }

        if (!descriptor) {

                descriptor = journal_get_descriptor_buffer(journal);

                if (!descriptor)

                        return;

                header = (journal_header_t *) &jh2bh(descriptor)->b_data[0];

                header->h_magic     = htonl(JFS_MAGIC_NUMBER);

                header->h_blocktype = htonl(JFS_REVOKE_BLOCK);

                header->h_sequence  = htonl(transaction->t_tid);

                /* Record it so that we can wait for IO completion later */

                JBUFFER_TRACE(descriptor, "file as BJ_LogCtl");

                journal_file_buffer(descriptor, transaction, BJ_LogCtl);

                offset = sizeof(journal_revoke_header_t);

                *descriptorp = descriptor;

        }

        * ((unsigned int *)(&jh2bh(descriptor)->b_data[offset])) =

                htonl(record->blocknr);

        offset += 4;

        *offsetp = offset;

}

/*

 * Flush a revoke descriptor out to the journal.  If we are aborting,

 * this is a noop; otherwise we are generating a buffer which needs to

 * be waited for during commit, so it has to go onto the appropriate

 * journal buffer list.

 */

static void flush_descriptor(journal_t *journal,

                             struct journal_head *descriptor,

                             int offset)

{

        journal_revoke_header_t *header;

        if (is_journal_aborted(journal)) {

                JBUFFER_TRACE(descriptor, "brelse");

                unlock_buffer(jh2bh(descriptor));

                __brelse(jh2bh(descriptor));

                return;

        }

        header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;

        header->r_count = htonl(offset);

        set_bit(BH_JWrite, &jh2bh(descriptor)->b_state);

        {

                struct buffer_head *bh = jh2bh(descriptor);

                BUFFER_TRACE(bh, "write");

                clear_bit(BH_Dirty, &bh->b_state);

                bh->b_end_io = journal_end_buffer_io_sync;

                submit_bh(WRITE, bh);

        }

}

#endif

/*

 * Revoke support for recovery.

 *

 * Recovery needs to be able to:

 *

 *  record all revoke records, including the tid of the latest instance

 *  of each revoke in the journal

 *

 *  check whether a given block in a given transaction should be replayed

 *  (ie. has not been revoked by a revoke record in that or a subsequent

 *  transaction)

 *

 *  empty the revoke table after recovery.

 */

/*

 * First, setting revoke records.  We create a new revoke record for

 * every block ever revoked in the log as we scan it for recovery, and

 * we update the existing records if we find multiple revokes for a

 * single block.

 */

int journal_set_revoke(journal_t *journal,

                       unsigned long blocknr,

                       tid_t sequence)

{

        struct jbd_revoke_record_s *record;

        record = find_revoke_record(journal, blocknr);

        if (record) {

                /* If we have multiple occurences, only record the

                 * latest sequence number in the hashed record */

                if (tid_gt(sequence, record->sequence))

                        record->sequence = sequence;

                return 0;

        }

        return insert_revoke_hash(journal, blocknr, sequence);

}

/*

 * Test revoke records.  For a given block referenced in the log, has

 * that block been revoked?  A revoke record with a given transaction

 * sequence number revokes all blocks in that transaction and earlier

 * ones, but later transactions still need replayed.

 */

int journal_test_revoke(journal_t *journal,

                        unsigned long blocknr,

                        tid_t sequence)

{

        struct jbd_revoke_record_s *record;

        record = find_revoke_record(journal, blocknr);

        if (!record)

                return 0;

        if (tid_gt(sequence, record->sequence))

                return 0;

        return 1;

}

/*

 * Finally, once recovery is over, we need to clear the revoke table so

 * that it can be reused by the running filesystem.

 */

void journal_clear_revoke(journal_t *journal)

{

        int i;

        struct list_head *hash_list;

        struct jbd_revoke_record_s *record;

        struct jbd_revoke_table_s *revoke;

        revoke = journal->j_revoke;

        for (i = 0; i < revoke->hash_size; i++) {

                hash_list = &revoke->hash_table[i];

                while (!list_empty(hash_list)) {

                        record = (struct jbd_revoke_record_s*) hash_list->next;

                        list_del(&record->hash);

                        kmem_cache_free(revoke_record_cache, record);

                }

        }

}