linux-ext4 - [PATCH v2 1/3] lib/ext2fs: record and show journal head block

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Date:   Fri, 17 Mar 2023 17:17:14 +0800
From:   Zhang Yi <yi.zhang@...weicloud.com>
To:     linux-ext4@...r.kernel.org
Cc:     tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz,
        yi.zhang@...wei.com, yi.zhang@...weicloud.com, yukuai3@...wei.com
Subject: [PATCH v2 1/3] lib/ext2fs: record and show journal head block

From: Zhang Yi <yi.zhang@...wei.com>

Add a new parameter into on-disk journal head block to record the head
block number of a clean journal image. This is used to support jbd2's
'JBD2_CYCLE_RECORD' option in kernel, which will be continue to record
new journal transactions between each mount, instead of always
recording from the first block. Note that the s_head is only uptodate
while the image is clean, we still need to walk through to find the head
block if the journal is not empty.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
 lib/e2p/ljs.c           | 3 +++
 lib/ext2fs/kernel-jbd.h | 6 ++++--
 lib/ext2fs/mkjournal.c  | 1 +
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/e2p/ljs.c b/lib/e2p/ljs.c
index 59728198..769f635a 100644
--- a/lib/e2p/ljs.c
+++ b/lib/e2p/ljs.c
@@ -108,6 +108,9 @@ void e2p_list_journal_super(FILE *f, char *journal_sb_buf,
 		"Journal start:            %u\n",
 		(unsigned int)ntohl(jsb->s_sequence),
 		(unsigned int)ntohl(jsb->s_start));
+	if (ntohl(jsb->s_start) == 0)
+		fprintf(f, "Journal head:             %u\n",
+			(unsigned int)ntohl(jsb->s_head));
 	if (nr_users != 1)
 		fprintf(f, "Journal number of users:  %u\n", nr_users);
 	if (jsb->s_feature_compat & e2p_be32(JBD2_FEATURE_COMPAT_CHECKSUM))
diff --git a/lib/ext2fs/kernel-jbd.h b/lib/ext2fs/kernel-jbd.h
index e5695006..1a7857c0 100644
--- a/lib/ext2fs/kernel-jbd.h
+++ b/lib/ext2fs/kernel-jbd.h
@@ -221,8 +221,10 @@ typedef struct journal_superblock_s
 	__u8	s_padding2[3];
 /* 0x0054 */
 	__be32	s_num_fc_blks;		/* Number of fast commit blocks */
-/* 0x0058 */
-	__be32	s_padding[41];
+	__be32	s_head;			/* blocknr of head of log, only uptodate
+					 * while the filesystem is clean */
+/* 0x005C */
+	__be32	s_padding[40];
 	__be32	s_checksum;		/* crc32c(superblock) */
 
 /* 0x0100 */
diff --git a/lib/ext2fs/mkjournal.c b/lib/ext2fs/mkjournal.c
index 54772dd5..24245bb7 100644
--- a/lib/ext2fs/mkjournal.c
+++ b/lib/ext2fs/mkjournal.c
@@ -79,6 +79,7 @@ errcode_t ext2fs_create_journal_superblock2(ext2_filsys fs,
 		jsb->s_nr_users = 0;
 		jsb->s_first = htonl(ext2fs_journal_sb_start(fs->blocksize) + 1);
 	}
+	jsb->s_head = jsb->s_first;
 
 	*ret_jsb = (char *) jsb;
 	return 0;
-- 
2.31.1