nilfs2: introduce nilfs_prepare_super

This function checks validity of super block pointers.
If first super block is invalid, it will swap the super blocks.
The function should be called before any super block information updates.
Caller must obtain nilfs->ns_sem.

Signed-off-by: Jiro SEKIBA <jir@unicus.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 1f7881ca01c4..9e680a93b13a 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2408,6 +2408,7 @@ static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
 {
         struct nilfs_sb_info *sbi = sci->sc_sbi;
         struct the_nilfs *nilfs = sbi->s_nilfs;
+        struct nilfs_super_block **sbp;
         int err = 0;
 
         nilfs_segctor_accept(sci);
@@ -2423,8 +2424,11 @@ static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
                 if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) &&
                     nilfs_discontinued(nilfs)) {
                         down_write(&nilfs->ns_sem);
-                        err = nilfs_commit_super(
-                                sbi, nilfs_altsb_need_update(nilfs));
+                        err = -EIO;
+                        sbp = nilfs_prepare_super(sbi);
+                        if (likely(sbp))
+                                err = nilfs_commit_super(
+                                        sbi, nilfs_altsb_need_update(nilfs));
                         up_write(&nilfs->ns_sem);
                 }
         }