[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.

This patch introduces nilfs_write_log_cursor to advance log cursor
one of super blocks.  To update super block information other than
log cursor, caller of nilfs_commit_super must set the information on both
super blocks.

Signed-off-by: Jiro SEKIBA <jir-hfpbi5WX9J54Eiagz67IpQ@public.gmane.org>
---
 fs/nilfs2/nilfs.h     |    1 +
 fs/nilfs2/segment.c   |   11 +-----
 fs/nilfs2/super.c     |   88 +++++++++++++++++++++++++++++++++----------------
 fs/nilfs2/the_nilfs.c |    2 +-
 fs/nilfs2/the_nilfs.h |   23 ++++++++----
 5 files changed, 78 insertions(+), 47 deletions(-)

diff --git a/fs/nilfs2/nilfs.h b/fs/nilfs2/nilfs.h
index 9805d35..581561b 100644
--- a/fs/nilfs2/nilfs.h
+++ b/fs/nilfs2/nilfs.h
@@ -270,6 +270,7 @@ extern struct nilfs_super_block *
 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_write_log_cursor(struct nilfs_sb_info *);
 extern struct nilfs_super_block **nilfs_prepare_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);
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index d42e5ee..ca81f3a 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2488,15 +2488,8 @@ static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
 		if (mode != SC_FLUSH_DAT)
 			atomic_set(&nilfs->ns_ndirtyblks, 0);
 		if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) &&
-		    nilfs_discontinued(nilfs)) {
-			down_write(&nilfs->ns_sem);
-			if (likely(nilfs_prepare_super(sbi)))
-				err = nilfs_commit_super(
-					sbi, nilfs_altsb_need_update(nilfs));
-			else
-				err = -EIO;
-			up_write(&nilfs->ns_sem);
-		}
+		    nilfs_discontinued(nilfs))
+			err = nilfs_write_log_cursor(sbi);
 	}
 
 	nilfs_segctor_notify(sci, mode, err);
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index a452e90..14099ae 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -102,7 +102,8 @@ void nilfs_error(struct super_block *sb, const char *function,
 			nilfs->ns_mount_state |= NILFS_ERROR_FS;
 			sbp = nilfs_prepare_super(sbi);
 			if (likely(sbp)) {
-				sbp[0]->s_state |= cpu_to_le16(NILFS_ERROR_FS);
+				nilfs_super_set_state(sbp,
+				sbp[0]->s_state | cpu_to_le16(NILFS_ERROR_FS));
 				nilfs_commit_super(sbi, 1);
 			}
 		}
@@ -229,6 +230,8 @@ 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;
 		}
@@ -248,6 +251,13 @@ 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) {
@@ -281,38 +291,60 @@ 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;
-	sector_t nfreeblocks;
 	time_t t;
-	int err;
-
-	/* nilfs->ns_sem must be locked by the caller. */
-	err = nilfs_count_free_blocks(nilfs, &nfreeblocks);
-	if (unlikely(err)) {
-		printk(KERN_ERR "NILFS: failed to count free blocks\n");
-		return err;
-	}
-	spin_lock(&nilfs->ns_last_segment_lock);
-	sbp[0]->s_last_seq = cpu_to_le64(nilfs->ns_last_seq);
-	sbp[0]->s_last_pseg = cpu_to_le64(nilfs->ns_last_pseg);
-	sbp[0]->s_last_cno = cpu_to_le64(nilfs->ns_last_cno);
-	spin_unlock(&nilfs->ns_last_segment_lock);
 
 	t = get_seconds();
 	nilfs->ns_sbwtime[0] = t;
-	sbp[0]->s_free_blocks_count = cpu_to_le64(nfreeblocks);
 	sbp[0]->s_wtime = cpu_to_le64(t);
 	sbp[0]->s_sum = 0;
 	sbp[0]->s_sum = cpu_to_le32(crc32_le(nilfs->ns_crc_seed,
 					     (unsigned char *)sbp[0],
 					     nilfs->ns_sbsize));
 	if (dupsb && sbp[1]) {
-		memcpy(sbp[1], sbp[0], nilfs->ns_sbsize);
 		nilfs->ns_sbwtime[1] = t;
+		sbp[1]->s_wtime = sbp[0]->s_wtime;
+		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);
 }
 
+int nilfs_write_log_cursor(struct nilfs_sb_info *sbi)
+{
+	struct the_nilfs *nilfs = sbi->s_nilfs;
+	struct nilfs_super_block **sbp;
+	sector_t nfreeblocks;
+	int err;
+
+	down_write(&nilfs->ns_sem);
+	sbp = nilfs_prepare_super(sbi);
+	if (unlikely(!sbp))  {
+		err = -EIO;
+		goto out;
+	}
+
+	err = nilfs_count_free_blocks(nilfs, &nfreeblocks);
+	if (unlikely(err)) {
+		printk(KERN_ERR "NILFS: failed to count free blocks\n");
+		goto out;
+	}
+	spin_lock(&nilfs->ns_last_segment_lock);
+	sbp[0]->s_last_seq = cpu_to_le64(nilfs->ns_last_seq);
+	sbp[0]->s_last_pseg = cpu_to_le64(nilfs->ns_last_pseg);
+	sbp[0]->s_last_cno = cpu_to_le64(nilfs->ns_last_cno);
+	spin_unlock(&nilfs->ns_last_segment_lock);
+
+	sbp[0]->s_free_blocks_count = cpu_to_le64(nfreeblocks);
+
+	err = nilfs_commit_super(sbi, 0);
+out:
+	up_write(&nilfs->ns_sem);
+	return err;
+}
+
 static void nilfs_put_super(struct super_block *sb)
 {
 	struct nilfs_sb_info *sbi = NILFS_SB(sb);
@@ -327,7 +359,8 @@ static void nilfs_put_super(struct super_block *sb)
 		down_write(&nilfs->ns_sem);
 		sbp = nilfs_prepare_super(sbi);
 		if (likely(sbp)) {
-			sbp[0]->s_state = cpu_to_le16(nilfs->ns_mount_state);
+			nilfs_super_set_state(sbp,
+				cpu_to_le16(nilfs->ns_mount_state));
 			nilfs_commit_super(sbi, 1);
 		}
 		up_write(&nilfs->ns_sem);
@@ -356,11 +389,8 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
 	if (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);
-	up_write(&nilfs->ns_sem);
-
+	if (nilfs_sb_dirty(nilfs))
+		nilfs_write_log_cursor(sbi);
 	return err;
 }
 
@@ -675,13 +705,13 @@ static int nilfs_setup_super(struct nilfs_sb_info *sbi)
 #endif
 	}
 	if (!max_mnt_count)
-		sbp[0]->s_max_mnt_count = cpu_to_le16(NILFS_DFL_MAX_MNT_COUNT);
-
-	sbp[0]->s_mnt_count = cpu_to_le16(mnt_count + 1);
-	sbp[0]->s_state =
-		cpu_to_le16(le16_to_cpu(sbp[0]->s_state) & ~NILFS_VALID_FS);
+		nilfs_super_set_max_mnt_count(sbp,
+				cpu_to_le16(NILFS_DFL_MAX_MNT_COUNT));
 
-	sbp[0]->s_mtime = cpu_to_le64(get_seconds());
+	nilfs_super_set_mnt_count(sbp, cpu_to_le16(mnt_count + 1));
+	nilfs_super_set_state(sbp,
+		cpu_to_le16(le16_to_cpu(sbp[0]->s_state) & ~NILFS_VALID_FS));
+	nilfs_super_set_mtime(sbp, cpu_to_le64(get_seconds()));
 	return nilfs_commit_super(sbi, 1);
 }
 
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index e8f2f1f..923faa7 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -329,7 +329,7 @@ int load_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
 	sbp = nilfs_prepare_super(sbi);
 	if (likely(sbp)) {
 		nilfs->ns_mount_state |= NILFS_VALID_FS;
-		sbp[0]->s_state = cpu_to_le16(nilfs->ns_mount_state);
+		nilfs_super_set_state(sbp, cpu_to_le16(nilfs->ns_mount_state));
 		err = nilfs_commit_super(sbi, 1);
 	} else
 		err = -EIO;
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 1ab9745..1bc8994 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -201,9 +201,23 @@ THE_NILFS_FNS(DISCONTINUED, discontinued)
 THE_NILFS_FNS(GC_RUNNING, gc_running)
 THE_NILFS_FNS(SB_DIRTY, sb_dirty)
 
+#define NILFS_SUPER_SET_FN(name, type)				\
+static inline void nilfs_super_set_##name(			\
+			struct nilfs_super_block **sbp,		\
+			type val)				\
+{								\
+	sbp[0]->s_##name = val;					\
+	if (sbp[1] && sbp[1]->s_magic == NILFS_SUPER_MAGIC)	\
+		sbp[1]->s_##name = val;				\
+}
+
+NILFS_SUPER_SET_FN(state, __le16)
+NILFS_SUPER_SET_FN(mnt_count, __le16)
+NILFS_SUPER_SET_FN(max_mnt_count, __le16)
+NILFS_SUPER_SET_FN(mtime, __le64)
+
 /* Minimum interval of periodical update of superblocks (in seconds) */
 #define NILFS_SB_FREQ		10
-#define NILFS_ALTSB_FREQ	60  /* spare superblock */
 
 static inline int nilfs_sb_need_update(struct the_nilfs *nilfs)
 {
@@ -212,13 +226,6 @@ static inline int nilfs_sb_need_update(struct the_nilfs *nilfs)
 		 t > nilfs->ns_sbwtime[0] + NILFS_SB_FREQ;
 }
 
-static inline int nilfs_altsb_need_update(struct the_nilfs *nilfs)
-{
-	u64 t = get_seconds();
-	struct nilfs_super_block **sbp = nilfs->ns_sbp;
-	return sbp[1] && t > nilfs->ns_sbwtime[1] + NILFS_ALTSB_FREQ;
-}
-
 void nilfs_set_last_segment(struct the_nilfs *, sector_t, u64, __u64);
 struct the_nilfs *find_or_create_nilfs(struct block_device *);
 void put_nilfs(struct the_nilfs *);
-- 
1.5.6.5

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