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recovery.c

/*
 * linux/fs/recovery.c
 * 
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1999
 *
 * Copyright 1999-2000 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.
 *
 * Journal recovery routines for the generic filesystem journaling code;
 * part of the ext2fs journaling system.  
 */

#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>
#endif

/*
 * Maintain information about the progress of the recovery job, so that
 * the different passes can carry information between them. 
 */
struct recovery_info 
{
      tid_t       start_transaction;      
      tid_t       end_transaction;
      
      int         nr_replays;
      int         nr_revokes;
      int         nr_revoke_hits;
};

enum passtype {PASS_SCAN, PASS_REVOKE, PASS_REPLAY};
static int do_one_pass(journal_t *journal,
                        struct recovery_info *info, enum passtype pass);
static int scan_revoke_records(journal_t *, struct buffer_head *,
                        tid_t, struct recovery_info *);

#ifdef __KERNEL__

/* Release readahead buffers after use */
void journal_brelse_array(struct buffer_head *b[], int n)
{
      while (--n >= 0)
            brelse (b[n]);
}


/*
 * When reading from the journal, we are going through the block device
 * layer directly and so there is no readahead being done for us.  We
 * need to implement any readahead ourselves if we want it to happen at
 * all.  Recovery is basically one long sequential read, so make sure we
 * do the IO in reasonably large chunks.
 *
 * This is not so critical that we need to be enormously clever about
 * the readahead size, though.  128K is a purely arbitrary, good-enough
 * fixed value.
 */

#define MAXBUF 8
static int do_readahead(journal_t *journal, unsigned int start)
{
      int err;
      unsigned int max, nbufs, next;
      unsigned long blocknr;
      struct buffer_head *bh;
      
      struct buffer_head * bufs[MAXBUF];
      
      /* Do up to 128K of readahead */
      max = start + (128 * 1024 / journal->j_blocksize);
      if (max > journal->j_maxlen)
            max = journal->j_maxlen;

      /* Do the readahead itself.  We'll submit MAXBUF buffer_heads at
       * a time to the block device IO layer. */
      
      nbufs = 0;
      
      for (next = start; next < max; next++) {
            err = journal_bmap(journal, next, &blocknr);

            if (err) {
                  printk (KERN_ERR "JBD: bad block at offset %u\n",
                        next);
                  goto failed;
            }

            bh = getblk(journal->j_dev, blocknr, journal->j_blocksize);
            if (!bh) {
                  err = -ENOMEM;
                  goto failed;
            }

            if (!buffer_uptodate(bh) && !buffer_locked(bh)) {
                  bufs[nbufs++] = bh;
                  if (nbufs == MAXBUF) {
                        ll_rw_block(READ, nbufs, bufs);
                        journal_brelse_array(bufs, nbufs);
                        nbufs = 0;
                  }
            } else
                  brelse(bh);
      }

      if (nbufs)
            ll_rw_block(READ, nbufs, bufs);
      err = 0;

failed:     
      if (nbufs) 
            journal_brelse_array(bufs, nbufs);
      return err;
}

#endif /* __KERNEL__ */


/*
 * Read a block from the journal
 */

static int jread(struct buffer_head **bhp, journal_t *journal, 
             unsigned int offset)
{
      int err;
      unsigned long blocknr;
      struct buffer_head *bh;

      *bhp = NULL;

      J_ASSERT (offset < journal->j_maxlen);
      
      err = journal_bmap(journal, offset, &blocknr);

      if (err) {
            printk (KERN_ERR "JBD: bad block at offset %u\n",
                  offset);
            return err;
      }

      bh = getblk(journal->j_dev, blocknr, journal->j_blocksize);
      if (!bh)
            return -ENOMEM;

      if (!buffer_uptodate(bh)) {
            /* If this is a brand new buffer, start readahead.
                   Otherwise, we assume we are already reading it.  */
            if (!buffer_req(bh))
                  do_readahead(journal, offset);
            wait_on_buffer(bh);
      }

      if (!buffer_uptodate(bh)) {
            printk (KERN_ERR "JBD: Failed to read block at offset %u\n",
                  offset);
            brelse(bh);
            return -EIO;
      }

      *bhp = bh;
      return 0;
}


/*
 * Count the number of in-use tags in a journal descriptor block.
 */

static int count_tags(struct buffer_head *bh, int size)
{
      char *                  tagp;
      journal_block_tag_t *   tag;
      int               nr = 0;

      tagp = &bh->b_data[sizeof(journal_header_t)];

      while ((tagp - bh->b_data + sizeof(journal_block_tag_t)) <= size) {
            tag = (journal_block_tag_t *) tagp;

            nr++;
            tagp += sizeof(journal_block_tag_t);
            if (!(tag->t_flags & htonl(JFS_FLAG_SAME_UUID)))
                  tagp += 16;

            if (tag->t_flags & htonl(JFS_FLAG_LAST_TAG))
                  break;
      }

      return nr;
}


/* Make sure we wrap around the log correctly! */
#define wrap(journal, var)                                  \
do {                                                  \
      if (var >= (journal)->j_last)                         \
            var -= ((journal)->j_last - (journal)->j_first);      \
} while (0)

/*
 * journal_recover
 *
 * The primary function for recovering the log contents when mounting a
 * journaled device.  
 * 
 * Recovery is done in three passes.  In the first pass, we look for the
 * end of the log.  In the second, we assemble the list of revoke
 * blocks.  In the third and final pass, we replay any un-revoked blocks
 * in the log.  
 */

int journal_recover(journal_t *journal)
{
      int               err;
      journal_superblock_t *  sb;

      struct recovery_info    info;
      
      memset(&info, 0, sizeof(info));
      sb = journal->j_superblock;
      
      /* 
       * The journal superblock's s_start field (the current log head)
       * is always zero if, and only if, the journal was cleanly
       * unmounted.  
       */

      if (!sb->s_start) {
            jbd_debug(1, "No recovery required, last transaction %d\n",
                    ntohl(sb->s_sequence));
            journal->j_transaction_sequence = ntohl(sb->s_sequence) + 1;
            return 0;
      }
      

      err = do_one_pass(journal, &info, PASS_SCAN);
      if (!err)
            err = do_one_pass(journal, &info, PASS_REVOKE);
      if (!err)
            err = do_one_pass(journal, &info, PASS_REPLAY);

      jbd_debug(0, "JBD: recovery, exit status %d, "
              "recovered transactions %u to %u\n",
              err, info.start_transaction, info.end_transaction);
      jbd_debug(0, "JBD: Replayed %d and revoked %d/%d blocks\n", 
              info.nr_replays, info.nr_revoke_hits, info.nr_revokes);

      /* Restart the log at the next transaction ID, thus invalidating
       * any existing commit records in the log. */
      journal->j_transaction_sequence = ++info.end_transaction;
            
      journal_clear_revoke(journal);
      fsync_no_super(journal->j_fs_dev);
      return err;
}

/*
 * journal_skip_recovery
 *
 * Locate any valid recovery information from the journal and set up the
 * journal structures in memory to ignore it (presumably because the
 * caller has evidence that it is out of date).  
 *
 * We perform one pass over the journal to allow us to tell the user how
 * much recovery information is being erased, and to let us initialise
 * the journal transaction sequence numbers to the next unused ID. 
 */

int journal_skip_recovery(journal_t *journal)
{
      int               err;
      journal_superblock_t *  sb;

      struct recovery_info    info;
      
      memset (&info, 0, sizeof(info));
      sb = journal->j_superblock;
      
      err = do_one_pass(journal, &info, PASS_SCAN);

      if (err) {
            printk(KERN_ERR "JBD: error %d scanning journal\n", err);
            ++journal->j_transaction_sequence;
      } else {
#ifdef CONFIG_JBD_DEBUG
            int dropped = info.end_transaction - ntohl(sb->s_sequence);
#endif
            
            jbd_debug(0, 
                    "JBD: ignoring %d transaction%s from the journal.\n",
                    dropped, (dropped == 1) ? "" : "s");
            journal->j_transaction_sequence = ++info.end_transaction;
      }

      journal->j_tail = 0;
      
      return err;
}

static int do_one_pass(journal_t *journal,
                  struct recovery_info *info, enum passtype pass)
{
      
      unsigned int            first_commit_ID, next_commit_ID;
      unsigned long           next_log_block;
      int               err, success = 0;
      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;
      MAX_BLOCKS_PER_DESC = ((journal->j_blocksize-sizeof(journal_header_t))
                         / sizeof(journal_block_tag_t));

      /* 
       * First thing is to establish what we expect to find in the log
       * (in terms of transaction IDs), and where (in terms of log
       * block offsets): query the superblock.  
       */

      sb = journal->j_superblock;
      next_commit_ID = ntohl(sb->s_sequence);
      next_log_block = ntohl(sb->s_start);

      first_commit_ID = next_commit_ID;
      if (pass == PASS_SCAN)
            info->start_transaction = first_commit_ID;

      jbd_debug(1, "Starting recovery pass %d\n", pass);

      /*
       * Now we walk through the log, transaction by transaction,
       * making sure that each transaction has a commit block in the
       * expected place.  Each complete transaction gets replayed back
       * into the main filesystem. 
       */

      while (1) {
            int               flags;
            char *                  tagp;
            journal_block_tag_t *   tag;
            struct buffer_head *    obh;
            struct buffer_head *    nbh;
            
            /* If we already know where to stop the log traversal,
             * check right now that we haven't gone past the end of
             * the log. */
            
            if (pass != PASS_SCAN)
                  if (tid_geq(next_commit_ID, info->end_transaction))
                        break;

            jbd_debug(2, "Scanning for sequence ID %u at %lu/%lu\n",
                    next_commit_ID, next_log_block, journal->j_last);

            /* Skip over each chunk of the transaction looking
             * either the next descriptor block or the final commit
             * record. */
            
            jbd_debug(3, "JBD: checking block %ld\n", next_log_block);
            err = jread(&bh, journal, next_log_block);
            if (err)
                  goto failed;

            next_log_block++;
            wrap(journal, next_log_block);
            
            /* What kind of buffer is it? 
             * 
             * If it is a descriptor block, check that it has the
             * expected sequence number.  Otherwise, we're all done
             * here. */

            tmp = (journal_header_t *)bh->b_data;
            
            if (tmp->h_magic != htonl(JFS_MAGIC_NUMBER)) {
                  brelse(bh);
                  break;
            }

            blocktype = ntohl(tmp->h_blocktype);
            sequence = ntohl(tmp->h_sequence);
            jbd_debug(3, "Found magic %d, sequence %d\n", 
                    blocktype, sequence);
            
            if (sequence != next_commit_ID) {
                  brelse(bh);
                  break;
            }
            
            /* OK, we have a valid descriptor block which matches
             * all of the sequence number checks.  What are we going
             * to do with it?  That depends on the pass... */

            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) {
                        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 = ntohl(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 = ntohl(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;
                              }

                              memcpy(nbh->b_data, obh->b_data,
                                          journal->j_blocksize);
                              if (flags & JFS_FLAG_ESCAPE) {
                                    *((unsigned int *)bh->b_data) =
                                          htonl(JFS_MAGIC_NUMBER);
                              }

                              BUFFER_TRACE(nbh, "marking dirty");
                              mark_buffer_dirty(nbh);
                              BUFFER_TRACE(nbh, "marking uptodate");
                              mark_buffer_uptodate(nbh, 1);
                              ++info->nr_replays;
                              /* ll_rw_block(WRITE, 1, &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;

            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;

            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;
                  }

                  err = scan_revoke_records(journal, bh,
                                      next_commit_ID, info);
                  brelse(bh);
                  if (err)
                        goto failed;
                  continue;

            default:
                  jbd_debug(3, "Unrecognised magic %d, end of scan.\n",
                          blocktype);
                  goto done;
            }
      }

 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
       * log.  If the latter happened, then we know that the "current"
       * transaction marks the end of the valid log.
       */
      
      if (pass == PASS_SCAN)
            info->end_transaction = next_commit_ID;
      else {
            /* It's really bad news if different passes end up at
             * different places (but possible due to IO errors). */
            if (info->end_transaction != next_commit_ID) {
                  printk (KERN_ERR "JBD: recovery pass %d ended at "
                        "transaction %u, expected %u\n",
                        pass, next_commit_ID, info->end_transaction);
                  if (!success)
                        success = -EIO;
            }
      }

      return success;

 failed:
      return err;
}


/* Scan a revoke record, marking all blocks mentioned as revoked. */

static int scan_revoke_records(journal_t *journal, struct buffer_head *bh, 
                         tid_t sequence, struct recovery_info *info)
{
      journal_revoke_header_t *header;
      int offset, max;

      header = (journal_revoke_header_t *) bh->b_data;
      offset = sizeof(journal_revoke_header_t);
      max = ntohl(header->r_count);
      
      while (offset < max) {
            unsigned long blocknr;
            int err;
            
            blocknr = ntohl(* ((unsigned int *) (bh->b_data+offset)));
            offset += 4;
            err = journal_set_revoke(journal, blocknr, sequence);
            if (err)
                  return err;
            ++info->nr_revokes;
      }
      return 0;
}

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