revoke.c

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/*
 * linux/fs/jbd/revoke.c
 *
 * Written by Stephen C. Tweedie <[email protected]>, 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.
 *
 * We cache revoke status of a buffer in the current transaction in b_states
 * bits.  As the name says, revokevalid flag indicates that the cached revoke
 * status of a buffer is valid and we can rely on the cached status.
 *
 * 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.
 *
 * Locking rules:
 * We keep two hash tables of revoke records. One hashtable belongs to the
 * running transaction (is pointed to by journal->j_revoke), the other one
 * belongs to the committing transaction. Accesses to the second hash table
 * happen only from the kjournald and no other thread touches this table.  Also
 * journal_switch_revoke_table() which switches which hashtable belongs to the
 * running and which to the committing transaction is called only from
 * kjournald. Therefore we need no locks when accessing the hashtable belonging
 * to the committing transaction.
 *
 * All users operating on the hash table belonging to the running transaction
 * have a handle to the transaction. Therefore they are safe from kjournald
 * switching hash tables under them. For operations on the lists of entries in
 * the hash table j_revoke_lock is used.
 *
 * Finally, also replay code uses the hash tables but at this moment no one else
 * can touch them (filesystem isn't mounted yet) and hence no locking is
 * needed.
 */

#ifndef __KERNEL__
#include "jfs_user.h"
#else
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/bio.h>
#endif
#include <linux/log2.h>

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

static int insert_revoke_hash(journal_t *journal, unsigned int 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)];
    spin_lock(&journal->j_revoke_lock);
    list_add(&record->hash, hash_list);
    spin_unlock(&journal->j_revoke_lock);
    return 0;

oom:
    if (!journal_oom_retry)
        return -ENOMEM;
    jbd_debug(1, "ENOMEM in %s, retrying\n", __func__);
    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 int blocknr)
{
    struct list_head *hash_list;
    struct jbd_revoke_record_s *record;

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

    spin_lock(&journal->j_revoke_lock);
    record = (struct jbd_revoke_record_s *) hash_list->next;
    while (&(record->hash) != hash_list) {
        if (record->blocknr == blocknr) {
            spin_unlock(&journal->j_revoke_lock);
            return record;
        }
        record = (struct jbd_revoke_record_s *) record->hash.next;
    }
    spin_unlock(&journal->j_revoke_lock);
    return NULL;
}

void journal_destroy_revoke_caches(void)
{
    if (revoke_record_cache) {
        kmem_cache_destroy(revoke_record_cache);
        revoke_record_cache = NULL;
    }
    if (revoke_table_cache) {
        kmem_cache_destroy(revoke_table_cache);
        revoke_table_cache = NULL;
    }
}

int __init journal_init_revoke_caches(void)
{
    J_ASSERT(!revoke_record_cache);
    J_ASSERT(!revoke_table_cache);

    revoke_record_cache = kmem_cache_create("revoke_record",
                       sizeof(struct jbd_revoke_record_s),
                       0,
                       SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY,
                       NULL);
    if (!revoke_record_cache)
        goto record_cache_failure;

    revoke_table_cache = kmem_cache_create("revoke_table",
                       sizeof(struct jbd_revoke_table_s),
                       0, SLAB_TEMPORARY, NULL);
    if (!revoke_table_cache)
        goto table_cache_failure;

    return 0;

table_cache_failure:
    journal_destroy_revoke_caches();
record_cache_failure:
    return -ENOMEM;
}

static struct jbd_revoke_table_s *journal_init_revoke_table(int hash_size)
{
    int shift = 0;
    int tmp = hash_size;
    struct jbd_revoke_table_s *table;

    table = kmem_cache_alloc(revoke_table_cache, GFP_KERNEL);
    if (!table)
        goto out;

    while((tmp >>= 1UL) != 0UL)
        shift++;

    table->hash_size = hash_size;
    table->hash_shift = shift;
    table->hash_table =
        kmalloc(hash_size * sizeof(struct list_head), GFP_KERNEL);
    if (!table->hash_table) {
        kmem_cache_free(revoke_table_cache, table);
        table = NULL;
        goto out;
    }

    for (tmp = 0; tmp < hash_size; tmp++)
        INIT_LIST_HEAD(&table->hash_table[tmp]);

out:
    return table;
}

static void journal_destroy_revoke_table(struct jbd_revoke_table_s *table)
{
    int i;
    struct list_head *hash_list;

    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);
}

/* Initialise the revoke table for a given journal to a given size. */
int journal_init_revoke(journal_t *journal, int hash_size)
{
    J_ASSERT(journal->j_revoke_table[0] == NULL);
    J_ASSERT(is_power_of_2(hash_size));

    journal->j_revoke_table[0] = journal_init_revoke_table(hash_size);
    if (!journal->j_revoke_table[0])
        goto fail0;

    journal->j_revoke_table[1] = journal_init_revoke_table(hash_size);
    if (!journal->j_revoke_table[1])
        goto fail1;

    journal->j_revoke = journal->j_revoke_table[1];

    spin_lock_init(&journal->j_revoke_lock);

    return 0;

fail1:
    journal_destroy_revoke_table(journal->j_revoke_table[0]);
fail0:
    return -ENOMEM;
}

/* Destroy a journal's revoke table.  The table must already be empty! */
void journal_destroy_revoke(journal_t *journal)
{
    journal->j_revoke = NULL;
    if (journal->j_revoke_table[0])
        journal_destroy_revoke_table(journal->j_revoke_table[0]);
    if (journal->j_revoke_table[1])
        journal_destroy_revoke_table(journal->j_revoke_table[1]);
}


#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 int blocknr,
           struct buffer_head *bh_in)
{
    struct buffer_head *bh = NULL;
    journal_t *journal;
    struct block_device *bdev;
    int err;

    might_sleep();
    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;
    }

    bdev = journal->j_fs_dev;
    bh = bh_in;

    if (!bh) {
        bh = __find_get_block(bdev, 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 = __find_get_block(bdev, blocknr, journal->j_blocksize);
        if (bh2) {
            /* ... and it has RevokeValid status... */
            if (bh2 != bh && buffer_revokevalid(bh2))
                /* ...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, buffer_revoked(bh2));
            put_bh(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) {
        if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
                 "inconsistent data on disk")) {
            if (!bh_in)
                brelse(bh);
            return -EIO;
        }
        set_buffer_revoked(bh);
        set_buffer_revokevalid(bh);
        if (bh_in) {
            BUFFER_TRACE(bh_in, "call journal_forget");
            journal_forget(handle, bh_in);
        } else {
            BUFFER_TRACE(bh, "call brelse");
            __brelse(bh);
        }
    }

    jbd_debug(2, "insert revoke for block %u, bh_in=%p\n", blocknr, bh_in);
    err = insert_revoke_hash(journal, blocknr,
                handle->h_transaction->t_tid);
    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 buffer_revoked() 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.
 */
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_set_buffer_revokevalid(bh)) {
        need_cancel = test_clear_buffer_revoked(bh);
    } else {
        need_cancel = 1;
        clear_buffer_revoked(bh);
    }

    if (need_cancel) {
        record = find_revoke_record(journal, bh->b_blocknr);
        if (record) {
            jbd_debug(4, "cancelled existing revoke on "
                  "blocknr %llu\n", (unsigned long long)bh->b_blocknr);
            spin_lock(&journal->j_revoke_lock);
            list_del(&record->hash);
            spin_unlock(&journal->j_revoke_lock);
            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) {
        struct buffer_head *bh2;
        bh2 = __find_get_block(bh->b_bdev, bh->b_blocknr, bh->b_size);
        if (bh2) {
            if (bh2 != bh)
                clear_buffer_revoked(bh2);
            __brelse(bh2);
        }
    }
    return did_revoke;
}

/*
 * journal_clear_revoked_flags clears revoked flag of buffers in
 * revoke table to reflect there is no revoked buffer in the next
 * transaction which is going to be started.
 */
void journal_clear_buffer_revoked_flags(journal_t *journal)
{
    struct jbd_revoke_table_s *revoke = journal->j_revoke;
    int i = 0;

    for (i = 0; i < revoke->hash_size; i++) {
        struct list_head *hash_list;
        struct list_head *list_entry;
        hash_list = &revoke->hash_table[i];

        list_for_each(list_entry, hash_list) {
            struct jbd_revoke_record_s *record;
            struct buffer_head *bh;
            record = (struct jbd_revoke_record_s *)list_entry;
            bh = __find_get_block(journal->j_fs_dev,
                          record->blocknr,
                          journal->j_blocksize);
            if (bh) {
                clear_buffer_revoked(bh);
                __brelse(bh);
            }
        }
    }
}

/* journal_switch_revoke table select j_revoke for next transaction
 * we do not want to suspend any processing until all revokes are
 * written -bzzz
 */
void journal_switch_revoke_table(journal_t *journal)
{
    int i;

    if (journal->j_revoke == journal->j_revoke_table[0])
        journal->j_revoke = journal->j_revoke_table[1];
    else
        journal->j_revoke = journal->j_revoke_table[0];

    for (i = 0; i < journal->j_revoke->hash_size; i++)
        INIT_LIST_HEAD(&journal->j_revoke->hash_table[i]);
}

/*
 * Write revoke records to the journal for all entries in the current
 * revoke hash, deleting the entries as we go.
 */
void journal_write_revoke_records(journal_t *journal,
                  transaction_t *transaction, int write_op)
{
    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;

    /* select revoke table for committing transaction */
    revoke = journal->j_revoke == journal->j_revoke_table[0] ?
        journal->j_revoke_table[1] : journal->j_revoke_table[0];

    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, write_op);
            count++;
            list_del(&record->hash);
            kmem_cache_free(revoke_record_cache, record);
        }
    }
    if (descriptor)
        flush_descriptor(journal, descriptor, offset, write_op);
    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,
                    int write_op)
{
    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, write_op);
            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     = cpu_to_be32(JFS_MAGIC_NUMBER);
        header->h_blocktype = cpu_to_be32(JFS_REVOKE_BLOCK);
        header->h_sequence  = cpu_to_be32(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;
    }

    * ((__be32 *)(&jh2bh(descriptor)->b_data[offset])) =
        cpu_to_be32(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, int write_op)
{
    journal_revoke_header_t *header;
    struct buffer_head *bh = jh2bh(descriptor);

    if (is_journal_aborted(journal)) {
        put_bh(bh);
        return;
    }

    header = (journal_revoke_header_t *) jh2bh(descriptor)->b_data;
    header->r_count = cpu_to_be32(offset);
    set_buffer_jwrite(bh);
    BUFFER_TRACE(bh, "write");
    set_buffer_dirty(bh);
    write_dirty_buffer(bh, write_op);
}
#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 int blocknr,
               tid_t sequence)
{
    struct jbd_revoke_record_s *record;

    record = find_revoke_record(journal, blocknr);
    if (record) {
        /* If we have multiple occurrences, 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 int 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);
        }
    }
}