reiserfs: properly honor read-only devices

The reiserfs journal behaves inconsistently when determining whether to
allow a mount of a read-only device.

This is due to the use of the continue_replay variable to short circuit
the journal scanning.  If it's set, it's assumed that there are
transactions to replay, but there may not be.  If it's unset, it's assumed
that there aren't any, and that may not be the case either.

I've observed two failure cases:
1) Where a clean file system on a read-only device refuses to mount
2) Where a clean file system on a read-only device passes the
   optimization and then tries writing the journal header to update
   the latest mount id.

The former is easily observable by using a freshly created file system on
a read-only loopback device.

This patch moves the check into journal_read_transaction, where it can
bail out before it's about to replay a transaction.  That way it can go
through and skip transactions where appropriate, yet still refuse to mount
a file system with outstanding transactions.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/reiserfs/journal.c

@@ -2217,6 +2217,15 @@ static int journal_read_transaction(struct super_block *sb,
 		brelse(d_bh);
 		return 1;
 	}
+
+	if (bdev_read_only(sb->s_bdev)) {
+		reiserfs_warning(sb, "clm-2076",
+				 "device is readonly, unable to replay log");
+		brelse(c_bh);
+		brelse(d_bh);
+		return -EROFS;
+	}
+
 	trans_id = get_desc_trans_id(desc);
 	/* now we know we've got a good transaction, and it was inside the valid time ranges */
 	log_blocks = kmalloc(get_desc_trans_len(desc) *
@@ -2459,12 +2468,6 @@ static int journal_read(struct super_block *sb)
 		goto start_log_replay;
 	}
 
-	if (continue_replay && bdev_read_only(sb->s_bdev)) {
-		reiserfs_warning(sb, "clm-2076",
-				 "device is readonly, unable to replay log");
-		return -1;
-	}
-
 	/* ok, there are transactions that need to be replayed.  start with the first log block, find
 	 ** all the valid transactions, and pick out the oldest.
 	 */