[PATCH 2/2] nilfs2: sync super blocks in turns

[Jiro SEKIBA <jir-hfpbi5WX9J54Eiagz67IpQ@public.gmane.org>]

This will sync super blocks in turns instead of syncing duplicate
super blocks at the time.  This will help searching valid super root when
super block is written into disk before log is written, which is happen when
barrier-less block devices are unmounted uncleanly.
In the stiation, old super block likely points valid log.

Signed-off-by: Jiro SEKIBA <jir-hfpbi5WX9J54Eiagz67IpQ@public.gmane.org>
---
 fs/nilfs2/nilfs.h   |    1 +
 fs/nilfs2/segment.c |    8 +++++---
 fs/nilfs2/super.c   |   44 +++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/fs/nilfs2/nilfs.h b/fs/nilfs2/nilfs.h
index c8edffd..b8fd4d1 100644
--- a/fs/nilfs2/nilfs.h
+++ b/fs/nilfs2/nilfs.h
@@ -271,6 +271,7 @@ nilfs_read_super_block(struct super_block *, u64, int, struct buffer_head **);
 extern int nilfs_store_magic_and_option(struct super_block *,
 					struct nilfs_super_block *, char *);
 extern int nilfs_prepare_super(struct nilfs_sb_info *);
+extern int nilfs_update_super(struct nilfs_sb_info *);
 extern int nilfs_commit_super(struct nilfs_sb_info *, int);
 extern int nilfs_attach_checkpoint(struct nilfs_sb_info *, __u64);
 extern void nilfs_detach_checkpoint(struct nilfs_sb_info *);
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 72f779f..4801331 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2491,9 +2491,11 @@ static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
 		    nilfs_discontinued(nilfs)) {
 			down_write(&nilfs->ns_sem);
 			err = nilfs_prepare_super(sbi);
-			if (likely(!err))
-				err = nilfs_commit_super(
-					sbi, nilfs_altsb_need_update(nilfs));
+			if (likely(!err)) {
+				err = nilfs_update_super(sbi);
+				if (likely(!err))
+					err = nilfs_commit_super(sbi, 0);
+			}
 			up_write(&nilfs->ns_sem);
 		}
 	}
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 312b34a..9d0edfb 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -227,6 +227,8 @@ static int nilfs_sync_super(struct nilfs_sb_info *sbi, int dupsb)
 		printk(KERN_ERR
 		       "NILFS: unable to write superblock (err=%d)\n", err);
 		if (err == -EIO && nilfs->ns_sbh[1]) {
+			memcpy(nilfs->ns_sbp[1], nilfs->ns_sbp[0],
+			       nilfs->ns_sbsize);
 			nilfs_fall_back_super_block(nilfs);
 			goto retry;
 		}
@@ -246,6 +248,13 @@ static int nilfs_sync_super(struct nilfs_sb_info *sbi, int dupsb)
 				set_buffer_dirty(nilfs->ns_sbh[1]);
 				if (!sync_dirty_buffer(nilfs->ns_sbh[1]))
 					sbp = nilfs->ns_sbp[1];
+			} else {
+				int flip_bits = (nilfs->ns_cno & 0x0FL);
+				/* flip super block 9 to 7 ratio */
+				if (flip_bits == 0x08 || flip_bits == 0x0F) {
+					nilfs_swap_super_block(nilfs);
+					sbp = nilfs->ns_sbp[1];
+				}
 			}
 		}
 		if (sbp) {
@@ -275,7 +284,7 @@ int nilfs_prepare_super(struct nilfs_sb_info *sbi)
 	return 0;
 }
 
-int nilfs_commit_super(struct nilfs_sb_info *sbi, int dupsb)
+int nilfs_update_super(struct nilfs_sb_info *sbi)
 {
 	struct the_nilfs *nilfs = sbi->s_nilfs;
 	struct nilfs_super_block **sbp = nilfs->ns_sbp;
@@ -303,9 +312,31 @@ int nilfs_commit_super(struct nilfs_sb_info *sbi, int dupsb)
 	sbp[0]->s_sum = cpu_to_le32(crc32_le(nilfs->ns_crc_seed,
 					     (unsigned char *)sbp[0],
 					     nilfs->ns_sbsize));
+	return 0;
+}
+
+int nilfs_commit_super(struct nilfs_sb_info *sbi, int dupsb)
+{
+	struct the_nilfs *nilfs = sbi->s_nilfs;
+	struct nilfs_super_block **sbp = nilfs->ns_sbp;
+
+	/* nilfs->sem must be locked by the caller. */
 	if (dupsb && sbp[1]) {
-		memcpy(sbp[1], sbp[0], nilfs->ns_sbsize);
-		nilfs->ns_sbwtime[1] = t;
+		nilfs->ns_sbwtime[1] = nilfs->ns_sbwtime[0];
+		/* copy super block except s_last_cno, s_last_pseg,
+		   s_last_seq, s_free_blocks_count.
+		  Those are asymmetric members */
+		const int ctimeoff =
+			offsetof(struct nilfs_super_block, s_ctime);
+		memcpy(sbp[1], sbp[0],
+		       offsetof(struct nilfs_super_block, s_last_cno));
+		memcpy((unsigned char *)sbp[1] + ctimeoff,
+		       (unsigned char *)sbp[0] + ctimeoff,
+		       nilfs->ns_sbsize - ctimeoff);
+		sbp[1]->s_sum = 0;
+		sbp[1]->s_sum = cpu_to_le32(crc32_le(nilfs->ns_crc_seed,
+					    (unsigned char *)sbp[1],
+					    nilfs->ns_sbsize));
 	}
 	clear_nilfs_sb_dirty(nilfs);
 	return nilfs_sync_super(sbi, dupsb);
@@ -352,8 +383,11 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
 		err = nilfs_construct_segment(sb);
 
 	down_write(&nilfs->ns_sem);
-	if (nilfs_sb_dirty(nilfs) && likely(!nilfs_prepare_super(sbi)))
-		nilfs_commit_super(sbi, 1);
+	if (nilfs_sb_dirty(nilfs) && likely(!nilfs_prepare_super(sbi))) {
+		err = nilfs_update_super(sbi);
+		if (likely(!err))
+			nilfs_commit_super(sbi, 0);
+	}
 	up_write(&nilfs->ns_sem);
 
 	return err;
-- 
1.5.6.5

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