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Date: Tue, 11 Mar 2008 15:35:50 +0100
From: Jan Kara <jack@...e.cz>
To: Duane Griffin <duaneg@...da.com>
Cc: linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
Theodore Tso <tytso@....edu>, sct@...hat.com,
akpm@...ux-foundation.org, adilger@...sterfs.com
Subject: Re: [RFC, PATCH 4/6] jbd: refactor nested journal log recovery loop into separate functions
> The do_one_pass function iterates through the jbd log operating on blocks
> depending on the pass. During the replay pass descriptor blocks are processed
> by an inner loop which replays them. The nesting makes the code difficult to
> follow or to modify. Splitting the inner loop and replay code into separate
> functions simplifies matters.
>
> The refactored code no longer unnecessarily reads revoked data blocks, so
> potential read errors from such blocks will cause differing behaviour. Aside
> from that there should be no functional effect.
Hmm, if I read your patch correctly, previously we aborted journal
replay when we found a block with unknown block magic but now we
continue replaying. Why have you done such change? And similarly when
some error happened when parsing revoke records block...
Honza
>
> Signed-off-by: Duane Griffin <duaneg@...da.com>
> ---
>
> Note the TODO before the block read in the outer loop below. We could possibly
> attempt to continue after a failed read as we do when replaying descriptor
> blocks. However if it was a descriptor block we'd likely bomb out on the next
> iteration anyway, so I'm not sure it would be worth it. Thoughts?
>
> fs/jbd/recovery.c | 243 ++++++++++++++++++++++++++++-------------------------
> 1 files changed, 127 insertions(+), 116 deletions(-)
>
> diff --git a/fs/jbd/recovery.c b/fs/jbd/recovery.c
> index 2b8edf4..e2ac78f 100644
> --- a/fs/jbd/recovery.c
> +++ b/fs/jbd/recovery.c
> @@ -307,6 +307,101 @@ int journal_skip_recovery(journal_t *journal)
> return err;
> }
>
> +static int replay_data_block(
> + journal_t *journal, struct buffer_head *obh, char *data,
> + int flags, unsigned long blocknr)
> +{
> + struct buffer_head *nbh;
> +
> + /* Find a buffer for the new data being restored */
> + nbh = __getblk(journal->j_fs_dev, blocknr, journal->j_blocksize);
> + if (nbh == NULL)
> + return -ENOMEM;
> +
> + lock_buffer(nbh);
> + memcpy(nbh->b_data, obh->b_data, journal->j_blocksize);
> + if (flags & JFS_FLAG_ESCAPE)
> + *((__be32 *)data) = cpu_to_be32(JFS_MAGIC_NUMBER);
> +
> + BUFFER_TRACE(nbh, "marking dirty");
> + set_buffer_uptodate(nbh);
> + mark_buffer_dirty(nbh);
> + BUFFER_TRACE(nbh, "marking uptodate");
> + /* ll_rw_block(WRITE, 1, &nbh); */
> + unlock_buffer(nbh);
> + brelse(nbh);
> +
> + return 0;
> +}
> +
> +/* Replay a descriptor block: write all of the data blocks. */
> +static int replay_descriptor_block(
> + journal_t *journal, char *data,
> + unsigned int next_commit_ID,
> + unsigned long *next_log_block,
> + struct recovery_info *info)
> +{
> + int err;
> + int success = 0;
> + char *tagp;
> + unsigned long io_block;
> + struct buffer_head *obh;
> + unsigned long next = *next_log_block;
> +
> + tagp = &data[sizeof(journal_header_t)];
> + while ((tagp - data + sizeof(journal_block_tag_t)) <=
> + journal->j_blocksize) {
> + unsigned long blocknr;
> + journal_block_tag_t *tag = (journal_block_tag_t *) tagp;
> + int flags = be32_to_cpu(tag->t_flags);
> +
> + io_block = next++;
> + wrap(journal, next);
> + blocknr = be32_to_cpu(tag->t_blocknr);
> +
> + /* If the block has been revoked, then we're all done here. */
> + if (journal_test_revoke(journal, blocknr, next_commit_ID)) {
> + ++info->nr_revoke_hits;
> + goto skip_write;
> + }
> +
> + err = jread(&obh, journal, io_block);
> + if (err) {
> +
> + /* Recover what we can, but
> + * report failure at the end. */
> + success = err;
> + printk(KERN_ERR "JBD: IO error %d recovering "
> + "block %ld in log\n", err, io_block);
> + continue;
> + }
> + J_ASSERT(obh != NULL);
> +
> + err = replay_data_block(journal, obh, data, flags, blocknr);
> + if (err) {
> + brelse(obh);
> + printk(KERN_ERR "JBD: Out of memory during recovery\n");
> + success = err;
> + goto failed;
> + }
> +
> + ++info->nr_replays;
> + brelse(obh);
> +
> +skip_write:
> + tagp += sizeof(journal_block_tag_t);
> + if (!(flags & JFS_FLAG_SAME_UUID))
> + tagp += 16;
> +
> + if (flags & JFS_FLAG_LAST_TAG)
> + break;
> + }
> +
> + *next_log_block = next;
> +failed:
> + return success;
> +}
> +
> static int do_one_pass(journal_t *journal,
> struct recovery_info *info, enum passtype pass)
> {
> @@ -316,8 +411,6 @@ static int do_one_pass(journal_t *journal,
> journal_superblock_t * sb;
> journal_header_t * tmp;
> struct buffer_head * bh;
> - unsigned int sequence;
> - int blocktype;
>
> /* Precompute the maximum metadata descriptors in a descriptor block */
> int MAX_BLOCKS_PER_DESC;
> @@ -348,11 +441,8 @@ static int do_one_pass(journal_t *journal,
> */
>
> while (1) {
> - int flags;
> - char * tagp;
> - journal_block_tag_t * tag;
> - struct buffer_head * obh;
> - struct buffer_head * nbh;
> + int blocktype;
> + unsigned int sequence;
>
> cond_resched();
>
> @@ -371,10 +461,13 @@ static int do_one_pass(journal_t *journal,
> * either the next descriptor block or the final commit
> * record. */
>
> + /* TODO: Should we continue on error? */
> jbd_debug(3, "JBD: checking block %ld\n", next_log_block);
> err = jread(&bh, journal, next_log_block);
> - if (err)
> + if (err) {
> + success = err;
> goto failed;
> + }
>
> next_log_block++;
> wrap(journal, next_log_block);
> @@ -406,137 +499,57 @@ static int do_one_pass(journal_t *journal,
> * all of the sequence number checks. What are we going
> * to do with it? That depends on the pass... */
>
> - switch(blocktype) {
> + switch (blocktype) {
> case JFS_DESCRIPTOR_BLOCK:
> /* If it is a valid descriptor block, replay it
> * in pass REPLAY; otherwise, just skip over the
> * blocks it describes. */
> - if (pass != PASS_REPLAY) {
> + if (pass == PASS_REPLAY) {
> + err = replay_descriptor_block(
> + journal,
> + bh->b_data,
> + next_commit_ID,
> + &next_log_block,
> + info);
> + } else {
> next_log_block +=
> count_tags(bh, journal->j_blocksize);
> wrap(journal, next_log_block);
> - brelse(bh);
> - continue;
> }
> -
> - /* A descriptor block: we can now write all of
> - * the data blocks. Yay, useful work is finally
> - * getting done here! */
> -
> - tagp = &bh->b_data[sizeof(journal_header_t)];
> - while ((tagp - bh->b_data +sizeof(journal_block_tag_t))
> - <= journal->j_blocksize) {
> - unsigned long io_block;
> -
> - tag = (journal_block_tag_t *) tagp;
> - flags = be32_to_cpu(tag->t_flags);
> -
> - io_block = next_log_block++;
> - wrap(journal, next_log_block);
> - err = jread(&obh, journal, io_block);
> - if (err) {
> - /* Recover what we can, but
> - * report failure at the end. */
> - success = err;
> - printk (KERN_ERR
> - "JBD: IO error %d recovering "
> - "block %ld in log\n",
> - err, io_block);
> - } else {
> - unsigned long blocknr;
> -
> - J_ASSERT(obh != NULL);
> - blocknr = be32_to_cpu(tag->t_blocknr);
> -
> - /* If the block has been
> - * revoked, then we're all done
> - * here. */
> - if (journal_test_revoke
> - (journal, blocknr,
> - next_commit_ID)) {
> - brelse(obh);
> - ++info->nr_revoke_hits;
> - goto skip_write;
> - }
> -
> - /* Find a buffer for the new
> - * data being restored */
> - nbh = __getblk(journal->j_fs_dev,
> - blocknr,
> - journal->j_blocksize);
> - if (nbh == NULL) {
> - printk(KERN_ERR
> - "JBD: Out of memory "
> - "during recovery.\n");
> - err = -ENOMEM;
> - brelse(bh);
> - brelse(obh);
> - goto failed;
> - }
> -
> - lock_buffer(nbh);
> - memcpy(nbh->b_data, obh->b_data,
> - journal->j_blocksize);
> - if (flags & JFS_FLAG_ESCAPE) {
> - *((__be32 *)bh->b_data) =
> - cpu_to_be32(JFS_MAGIC_NUMBER);
> - }
> -
> - BUFFER_TRACE(nbh, "marking dirty");
> - set_buffer_uptodate(nbh);
> - mark_buffer_dirty(nbh);
> - BUFFER_TRACE(nbh, "marking uptodate");
> - ++info->nr_replays;
> - /* ll_rw_block(WRITE, 1, &nbh); */
> - unlock_buffer(nbh);
> - brelse(obh);
> - brelse(nbh);
> - }
> -
> - skip_write:
> - tagp += sizeof(journal_block_tag_t);
> - if (!(flags & JFS_FLAG_SAME_UUID))
> - tagp += 16;
> -
> - if (flags & JFS_FLAG_LAST_TAG)
> - break;
> - }
> -
> - brelse(bh);
> - continue;
> + break;
>
> case JFS_COMMIT_BLOCK:
> /* Found an expected commit block: not much to
> * do other than move on to the next sequence
> * number. */
> - brelse(bh);
> next_commit_ID++;
> - continue;
> + break;
>
> case JFS_REVOKE_BLOCK:
> /* If we aren't in the REVOKE pass, then we can
> * just skip over this block. */
> - if (pass != PASS_REVOKE) {
> - brelse(bh);
> - continue;
> + if (pass == PASS_REVOKE) {
> + err = scan_revoke_records(
> + journal, bh, next_commit_ID, info);
> }
> -
> - err = scan_revoke_records(journal, bh,
> - next_commit_ID, info);
> - brelse(bh);
> - if (err)
> - goto failed;
> - continue;
> + break;
>
> default:
> jbd_debug(3, "Unrecognised magic %d, end of scan.\n",
> blocktype);
> - brelse(bh);
> - goto done;
> + break;
> }
> +
> + brelse(bh);
> +
> + /* Immediately fail on OOM; on other errors try to recover
> + * as much as we can, but report the failure at the end. */
> + if (err)
> + success = err;
> + if (err == -ENOMEM)
> + goto failed;
> }
>
> - done:
> /*
> * We broke out of the log scan loop: either we came to the
> * known end of the log or we found an unexpected block in the
> @@ -558,10 +571,8 @@ static int do_one_pass(journal_t *journal,
> }
> }
>
> - return success;
> -
> failed:
> - return err;
> + return success;
> }
>
>
> --
> 1.5.3.7
>
> --
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--
Jan Kara <jack@...e.cz>
SuSE CR Labs
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