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ext4_journal: fix mistreating an empty journal as a bad one.

--- a/lwext4/ext4_journal.c

+++ b/lwext4/ext4_journal.c

@@ -74,6 +74,9 @@

 	/**@brief  Used as internal argument.*/

 	uint32_t this_trans_id;

+	/**@brief  No of transactions went through.*/

+	uint32_t trans_cnt;

+

 	/**@brief  RB-Tree storing revoke entries.*/

 	RB_HEAD(jbd_revoke, revoke_entry) revoke_root;

 };

@@ -1025,6 +1028,10 @@

 	/* We start iterating valid blocks in the whole journal.*/

 	start_trans_id = this_trans_id = jbd_get32(sb, sequence);

 	start_block = this_block = jbd_get32(sb, start);

+	if (action == ACTION_SCAN)

+		info->trans_cnt = 0;

+	else if (!info->trans_cnt)

+		log_end = true;

 	ext4_dbg(DEBUG_JBD, "Start of journal at trans id: %" PRIu32 "\n",

 			    start_trans_id);

@@ -1112,6 +1119,7 @@

 			 * we may now proceed to the next transaction.

 			 */

 			this_trans_id++;

+			info->trans_cnt++;

 			break;

 		case JBD_REVOKE_BLOCK:

 			if (!jbd_verify_meta_csum(jbd_fs, header)) {

@@ -1217,6 +1225,7 @@

 	uint32_t features_incompatible =

 			ext4_get32(&jbd_fs->inode_ref.fs->sb,

 				   features_incompatible);

+	struct ext4_block block = EXT4_BLOCK_ZERO();

 	features_incompatible |= EXT4_FINCOM_RECOVER;

 	ext4_set32(&jbd_fs->inode_ref.fs->sb,

 			features_incompatible,

@@ -1233,6 +1242,21 @@

 	journal->alloc_trans_id = 1;

 	journal->block_size = jbd_get32(&jbd_fs->sb, blocksize);

+

+	r = jbd_block_get_noread(jbd_fs,

+			 &block,

+			 journal->start);

+	if (r != EOK) {

+		memset(journal, 0, sizeof(struct jbd_journal));

+		return r;

+	}

+	memset(block.data, 0, journal->block_size);

+	ext4_bcache_set_dirty(block.buf);

+	r = jbd_block_set(jbd_fs, &block);

+	if (r != EOK) {

+		memset(journal, 0, sizeof(struct jbd_journal));

+		return r;

+	}

 	TAILQ_INIT(&journal->trans_queue);

 	TAILQ_INIT(&journal->cp_queue);