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From:   Zhang Yi <yi.zhang@huaweicloud.com>
To:     linux-ext4@vger.kernel.org
Cc:     tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.cz,
        yi.zhang@huawei.com, yi.zhang@huaweicloud.com, yukuai3@huawei.com
Subject: [RFC PATCH 1/2] jbd2: cycled record log on clean journal logging area
Date:   Thu, 19 Jan 2023 11:45:59 +0800
Message-Id: <20230119034600.3431194-2-yi.zhang@huaweicloud.com>
In-Reply-To: <20230119034600.3431194-1-yi.zhang@huaweicloud.com>
References: <20230119034600.3431194-1-yi.zhang@huaweicloud.com>
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From: Zhang Yi <yi.zhang@huawei.com>

For a newly mounted file system, the journal committing thread always
record log from the beginning of the journal area, no matter whether the
journal is clean or it has just been recovered. It is disadvantageous to
analysis corrupted file system image and locate the file system
inconsistency bugs. When we get a corrupted file system image and want
to find out what has happened, besides lookup the system log, one
effective may is to backtrack the journal log. But we may not always run
e2fsck before each mount and the default fsck -a mode also cannot always
find all inconsistencies, so it could left over some inconsistencies
into the next mount until we detect it. Finally, the transactions in the
journal may probably discontinuous and some relatively new transactions
has been covered, it becomes hard to analyse. So if we could records
transactions continuously between each mounts, we could acquire more
useful info from the journal.

 |Previous mount checkpointed/recovered logs|Current mount logs         |
 |{------}{---}{--------} ... {------}| ... |{======}{========}...000000|

This patch save the head blocknr in the superblock after flushing the
journal or unmounting the file system, let the next mount could continue
to record new transaction behind it. This change is backward compatible
because the old kernel does not care about the head blocknr of the
journal. It is also fine if we mount a clean old image without valid
head blocknr, we fail back to set it to s_first just like before.
Finally, for the case of mount an unclean file system, we could also get
the journal head easily after scanning the journal, it will continue to
record new transaction after the recovered transactions.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/jbd2/journal.c    | 18 ++++++++++++++++--
 fs/jbd2/recovery.c   | 22 +++++++++++++++++-----
 include/linux/jbd2.h |  9 +++++++--
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 2696f43e7239..41f0f5625e7c 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1557,8 +1557,21 @@ static int journal_reset(journal_t *journal)
 	journal->j_first = first;
 	journal->j_last = last;
 
-	journal->j_head = journal->j_first;
-	journal->j_tail = journal->j_first;
+	if (journal->j_flags & JBD2_CYCLE_RECORD) {
+		/*
+		 * Disable the cycled recording mode if the journal head block
+		 * number is not correct.
+		 */
+		if (journal->j_head < first || journal->j_head >= last) {
+			printk(KERN_WARNING "JBD2: Incorrect Journal head block %lu, "
+			       "disable journal_cycle_record\n",
+			       journal->j_head);
+			journal->j_head = journal->j_first;
+		}
+	} else {
+		journal->j_head = journal->j_first;
+	}
+	journal->j_tail = journal->j_head;
 	journal->j_free = journal->j_last - journal->j_first;
 
 	journal->j_tail_sequence = journal->j_transaction_sequence;
@@ -1730,6 +1743,7 @@ static void jbd2_mark_journal_empty(journal_t *journal, blk_opf_t write_flags)
 
 	sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
 	sb->s_start    = cpu_to_be32(0);
+	sb->s_head     = cpu_to_be32(journal->j_head);
 	if (jbd2_has_feature_fast_commit(journal)) {
 		/*
 		 * When journal is clean, no need to commit fast commit flag and
diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
index 8286a9ec122f..6f6bcb75fffe 100644
--- a/fs/jbd2/recovery.c
+++ b/fs/jbd2/recovery.c
@@ -29,6 +29,7 @@ struct recovery_info
 {
 	tid_t		start_transaction;
 	tid_t		end_transaction;
+	unsigned long	head_block;
 
 	int		nr_replays;
 	int		nr_revokes;
@@ -301,11 +302,11 @@ int jbd2_journal_recover(journal_t *journal)
 	 * is always zero if, and only if, the journal was cleanly
 	 * unmounted.
 	 */
-
 	if (!sb->s_start) {
-		jbd2_debug(1, "No recovery required, last transaction %d\n",
-			  be32_to_cpu(sb->s_sequence));
+		jbd2_debug(1, "No recovery required, last transaction %d, head block %u\n",
+			  be32_to_cpu(sb->s_sequence), be32_to_cpu(sb->s_head));
 		journal->j_transaction_sequence = be32_to_cpu(sb->s_sequence) + 1;
+		journal->j_head = be32_to_cpu(sb->s_head);
 		return 0;
 	}
 
@@ -324,6 +325,9 @@ int jbd2_journal_recover(journal_t *journal)
 	/* 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->j_head = info.head_block;
+	jbd2_debug(1, "JBD2: last transaction %d, head block %u\n",
+		  journal->j_transaction_sequence, journal->j_head);
 
 	jbd2_journal_clear_revoke(journal);
 	err2 = sync_blockdev(journal->j_fs_dev);
@@ -364,6 +368,7 @@ int jbd2_journal_skip_recovery(journal_t *journal)
 	if (err) {
 		printk(KERN_ERR "JBD2: error %d scanning journal\n", err);
 		++journal->j_transaction_sequence;
+		journal->j_head = journal->j_first;
 	} else {
 #ifdef CONFIG_JBD2_DEBUG
 		int dropped = info.end_transaction - 
@@ -373,6 +378,7 @@ int jbd2_journal_skip_recovery(journal_t *journal)
 			  dropped, (dropped == 1) ? "" : "s");
 #endif
 		journal->j_transaction_sequence = ++info.end_transaction;
+		journal->j_head = info.head_block;
 	}
 
 	journal->j_tail = 0;
@@ -462,7 +468,7 @@ 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;
+	unsigned long		next_log_block, head_block;
 	int			err, success = 0;
 	journal_superblock_t *	sb;
 	journal_header_t *	tmp;
@@ -485,6 +491,7 @@ static int do_one_pass(journal_t *journal,
 	sb = journal->j_superblock;
 	next_commit_ID = be32_to_cpu(sb->s_sequence);
 	next_log_block = be32_to_cpu(sb->s_start);
+	head_block = next_log_block;
 
 	first_commit_ID = next_commit_ID;
 	if (pass == PASS_SCAN)
@@ -809,6 +816,7 @@ static int do_one_pass(journal_t *journal,
 				if (commit_time < last_trans_commit_time)
 					goto ignore_crc_mismatch;
 				info->end_transaction = next_commit_ID;
+				info->head_block = head_block;
 
 				if (!jbd2_has_feature_async_commit(journal)) {
 					journal->j_failed_commit =
@@ -817,8 +825,10 @@ static int do_one_pass(journal_t *journal,
 					break;
 				}
 			}
-			if (pass == PASS_SCAN)
+			if (pass == PASS_SCAN) {
 				last_trans_commit_time = commit_time;
+				head_block = next_log_block;
+			}
 			brelse(bh);
 			next_commit_ID++;
 			continue;
@@ -868,6 +878,8 @@ static int do_one_pass(journal_t *journal,
 	if (pass == PASS_SCAN) {
 		if (!info->end_transaction)
 			info->end_transaction = next_commit_ID;
+		if (!info->head_block)
+			info->head_block = head_block;
 	} else {
 		/* It's really bad news if different passes end up at
 		 * different places (but possible due to IO errors). */
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 2170e0cc279d..d5843ebfa6ed 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -265,8 +265,10 @@ typedef struct journal_superblock_s
 	__u8	s_padding2[3];
 /* 0x0054 */
 	__be32	s_num_fc_blks;		/* Number of fast commit blocks */
-/* 0x0058 */
-	__u32	s_padding[41];
+	__be32	s_head;			/* blocknr of head of log, only uptodate
+					 * while the filesystem is clean */
+/* 0x005C */
+	__u32	s_padding[40];
 	__be32	s_checksum;		/* crc32c(superblock) */
 
 /* 0x0100 */
@@ -1392,6 +1394,9 @@ JBD2_FEATURE_INCOMPAT_FUNCS(fast_commit,	FAST_COMMIT)
 #define JBD2_ABORT_ON_SYNCDATA_ERR	0x040	/* Abort the journal on file
 						 * data write error in ordered
 						 * mode */
+#define JBD2_CYCLE_RECORD		0x080	/* Journal cycled record log on
+						 * clean and empty filesystem
+						 * logging area */
 #define JBD2_FAST_COMMIT_ONGOING	0x100	/* Fast commit is ongoing */
 #define JBD2_FULL_COMMIT_ONGOING	0x200	/* Full commit is ongoing */
 #define JBD2_JOURNAL_FLUSH_DISCARD	0x0001
-- 
2.31.1