linux-kernel - Re: [RFC PATCH v2] f2fs: record need_fsck in super

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Message-ID: <YyykoT0BdBrXfcrQ@google.com>
Date:   Thu, 22 Sep 2022 11:08:33 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] f2fs: record need_fsck in super_block

On 09/20, Chao Yu wrote:
> On 2022/9/20 8:56, Jaegeuk Kim wrote:
> > On 09/13, Chao Yu wrote:
> > > Once CP_ERROR_FLAG is set, checkpoint is disallowed to be triggered to
> > > persist CP_FSCK_FLAG, fsck won't repair the image due to lack of
> > > CP_FSCK_FLAG.
> > > 
> > > This patch proposes to persist newly introduced SB_NEED_FSCK flag into
> > > super block if CP_ERROR_FLAG and SBI_NEED_FSCK is set, later, once fsck
> > > detect this flag, it can check and repair corrupted image in time.
> > > 
> > > Signed-off-by: Chao Yu <chao@...nel.org>
> > > ---
> > > v2:
> > > - remove unneeded codes.
> > >   fs/f2fs/checkpoint.c    |  6 +++++-
> > >   fs/f2fs/f2fs.h          |  1 +
> > >   fs/f2fs/super.c         | 26 ++++++++++++++++++++++++++
> > >   include/linux/f2fs_fs.h |  5 ++++-
> > >   4 files changed, 36 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > > index c3119e4c890c..0836fce40394 100644
> > > --- a/fs/f2fs/checkpoint.c
> > > +++ b/fs/f2fs/checkpoint.c
> > > @@ -30,8 +30,12 @@ void f2fs_stop_checkpoint(struct f2fs_sb_info *sbi, bool end_io)
> > >   {
> > >   	f2fs_build_fault_attr(sbi, 0, 0);
> > >   	set_ckpt_flags(sbi, CP_ERROR_FLAG);
> > > -	if (!end_io)
> > > +	if (!end_io) {
> > >   		f2fs_flush_merged_writes(sbi);
> > > +
> > > +		if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
> > > +			f2fs_update_sb_flags(sbi, SB_NEED_FSCK);
> > 
> > Let's think of putting some more context in superblock, if we want to overwrite
> > it. E.g., a reason to stop checkpoint?
> 
> Good idea, maybe:
> Bit	Value				max number of type
> [0]	need fsck flag			1
> [1-5]	reason to stop checkpoint	32
> [6-13]	reason to fsck			256

How about just keeping the counters of the reasons? (e.g., EIO count which
stopped checkpoint)

#define MAX_CRASH_REASON 32
char array[MAX_CRASH_REASON];

> 
> Thanks
> 
> > 
> > > +	}
> > >   }
> > >   /*
> > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > > index dee7b67a17a6..1960a98c7555 100644
> > > --- a/fs/f2fs/f2fs.h
> > > +++ b/fs/f2fs/f2fs.h
> > > @@ -3556,6 +3556,7 @@ int f2fs_enable_quota_files(struct f2fs_sb_info *sbi, bool rdonly);
> > >   int f2fs_quota_sync(struct super_block *sb, int type);
> > >   loff_t max_file_blocks(struct inode *inode);
> > >   void f2fs_quota_off_umount(struct super_block *sb);
> > > +void f2fs_update_sb_flags(struct f2fs_sb_info *sbi, unsigned int flag);
> > >   int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover);
> > >   int f2fs_sync_fs(struct super_block *sb, int sync);
> > >   int f2fs_sanity_check_ckpt(struct f2fs_sb_info *sbi);
> > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > > index b8e5fe244596..c99ba840593d 100644
> > > --- a/fs/f2fs/super.c
> > > +++ b/fs/f2fs/super.c
> > > @@ -3846,6 +3846,32 @@ int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
> > >   	return err;
> > >   }
> > > +void f2fs_update_sb_flags(struct f2fs_sb_info *sbi, unsigned int flag)
> > > +{
> > > +	unsigned short s_flags;
> > > +	int err;
> > > +
> > > +	if (le16_to_cpu(F2FS_RAW_SUPER(sbi)->s_flags) & SB_NEED_FSCK)
> > > +		return;
> > > +
> > > +	f2fs_down_write(&sbi->sb_lock);
> > > +
> > > +	s_flags = le16_to_cpu(F2FS_RAW_SUPER(sbi)->s_flags);
> > > +
> > > +	if (s_flags & SB_NEED_FSCK)
> > > +		goto out_unlock;
> > > +
> > > +	F2FS_RAW_SUPER(sbi)->s_flags = cpu_to_le16(s_flags | SB_NEED_FSCK);
> > > +
> > > +	err = f2fs_commit_super(sbi, false);
> > > +	if (err) {
> > > +		f2fs_warn(sbi, "f2fs_commit_super fails to persist flag: %u, err:%d", flag, err);
> > > +		F2FS_RAW_SUPER(sbi)->s_flags = s_flags;
> > > +	}
> > > +out_unlock:
> > > +	f2fs_up_write(&sbi->sb_lock);
> > > +}
> > > +
> > >   static int f2fs_scan_devices(struct f2fs_sb_info *sbi)
> > >   {
> > >   	struct f2fs_super_block *raw_super = F2FS_RAW_SUPER(sbi);
> > > diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
> > > index d445150c5350..124176e2a42c 100644
> > > --- a/include/linux/f2fs_fs.h
> > > +++ b/include/linux/f2fs_fs.h
> > > @@ -73,6 +73,8 @@ struct f2fs_device {
> > >   	__le32 total_segments;
> > >   } __packed;
> > > +#define SB_NEED_FSCK			0x00000001	/* need fsck */
> > > +
> > >   struct f2fs_super_block {
> > >   	__le32 magic;			/* Magic Number */
> > >   	__le16 major_ver;		/* Major Version */
> > > @@ -116,7 +118,8 @@ struct f2fs_super_block {
> > >   	__u8 hot_ext_count;		/* # of hot file extension */
> > >   	__le16  s_encoding;		/* Filename charset encoding */
> > >   	__le16  s_encoding_flags;	/* Filename charset encoding flags */
> > > -	__u8 reserved[306];		/* valid reserved region */
> > > +	__le16 s_flags;			/* super block flags */
> > > +	__u8 reserved[304];		/* valid reserved region */
> > >   	__le32 crc;			/* checksum of superblock */
> > >   } __packed;
> > > -- 
> > > 2.25.1