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    SubjectRe: [PATCH 33/49] ext4: Add the journal checksum feature
    Hi,

    On Thu, 2008-01-24 at 13:24 -0800, Mingming Cao wrote:
    > -static int journal_write_commit_record(journal_t *journal,
    > - transaction_t *commit_transaction)
    > +static int journal_submit_commit_record(journal_t *journal,
    > + transaction_t *commit_transaction,
    > + struct buffer_head **cbh,
    > + __u32 crc32_sum)
    > {
    > struct journal_head *descriptor;
    > + struct commit_header *tmp;
    > struct buffer_head *bh;
    > - int i, ret;
    > + int ret;
    > int barrier_done = 0;
    >
    > if (is_journal_aborted(journal))
    > @@ -117,21 +122,33 @@ static int journal_write_commit_record(j
    >
    > bh = jh2bh(descriptor);
    >
    > - /* AKPM: buglet - add `i' to tmp! */
    > - for (i = 0; i < bh->b_size; i += 512) {
    > - journal_header_t *tmp = (journal_header_t*)bh->b_data;
    > - tmp->h_magic = cpu_to_be32(JBD2_MAGIC_NUMBER);
    > - tmp->h_blocktype = cpu_to_be32(JBD2_COMMIT_BLOCK);
    > - tmp->h_sequence = cpu_to_be32(commit_transaction->t_tid);
    > + tmp = (struct commit_header *)bh->b_data;
    > + tmp->h_magic = cpu_to_be32(JBD2_MAGIC_NUMBER);
    > + tmp->h_blocktype = cpu_to_be32(JBD2_COMMIT_BLOCK);
    > + tmp->h_sequence = cpu_to_be32(commit_transaction->t_tid);
    > +
    > + if (JBD2_HAS_COMPAT_FEATURE(journal,
    > + JBD2_FEATURE_COMPAT_CHECKSUM)) {
    > + tmp->h_chksum_type = JBD2_CRC32_CHKSUM;
    > + tmp->h_chksum_size = JBD2_CRC32_CHKSUM_SIZE;
    > + tmp->h_chksum[0] = cpu_to_be32(crc32_sum);
    > }
    >
    > - JBUFFER_TRACE(descriptor, "write commit block");
    > + JBUFFER_TRACE(descriptor, "submit commit block");
    > + lock_buffer(bh);
    > +
    get_bh() is missing here.
    bh refcount is decremented in journal_wait_on_commit_record(), but it is
    not incremented in journal_submit_commit_record().
    Thanks to Johann Lombardi for pointing this out.

    Comments.

    > set_buffer_dirty(bh);
    > - if (journal->j_flags & JBD2_BARRIER) {
    > + set_buffer_uptodate(bh);
    > + bh->b_end_io = journal_end_buffer_io_sync;
    > +
    > + if (journal->j_flags & JBD2_BARRIER &&
    > + !JBD2_HAS_COMPAT_FEATURE(journal,
    > + JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
    > set_buffer_ordered(bh);
    > barrier_done = 1;
    > }
    > - ret = sync_dirty_buffer(bh);
    > + ret = submit_bh(WRITE, bh);
    > +
    > /* is it possible for another commit to fail at roughly
    > * the same time as this one? If so, we don't want to
    > * trust the barrier flag in the super, but instead want
    > @@ -152,14 +169,72 @@ static int journal_write_commit_record(j
    > clear_buffer_ordered(bh);
    > set_buffer_uptodate(bh);
    > set_buffer_dirty(bh);
    > - ret = sync_dirty_buffer(bh);
    > + ret = submit_bh(WRITE, bh);
    > }
    > - put_bh(bh); /* One for getblk() */
    > - jbd2_journal_put_journal_head(descriptor);
    > + *cbh = bh;
    > + return ret;
    > +}
    > +
    > +/*
    > + * This function along with journal_submit_commit_record
    > + * allows to write the commit record asynchronously.
    > + */
    > +static int journal_wait_on_commit_record(struct buffer_head *bh)
    > +{
    > + int ret = 0;
    > +
    > + clear_buffer_dirty(bh);
    > + wait_on_buffer(bh);
    > +
    > + if (unlikely(!buffer_uptodate(bh)))
    > + ret = -EIO;
    > + put_bh(bh); /* One for getblk() */
    > + jbd2_journal_put_journal_head(bh2jh(bh));
    >
    > - return (ret == -EIO);
    > + return ret;
    > }
    >
    -Girish



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