linux-kernel - Re: [PATCH] f2fs: change the codes of checking CP_CRC_RECOVERY

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Date:   Fri, 24 Feb 2017 10:12:35 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Yunlong Song <yunlong.song@...wei.com>
Cc:     Chao Yu <yuchao0@...wei.com>, cm224.lee@...sung.com,
        chao@...nel.org, sylinux@....com, miaoxie@...wei.com,
        bintian.wang@...wei.com, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: change the codes of checking CP_CRC_RECOVERY_FLAG
 to macro

On 02/24, Yunlong Song wrote:
> On 2017/2/24 19:37, Chao Yu wrote:
> > On 2017/2/24 19:11, Yunlong Song wrote:
> >> I think we do not need to care about the CP_CRC_RECOVERY_FLAG status of old image, I mean we
> >> do not need to check the already-been-written node footer in the image, what we care about is the
> >> on-going-to-write node footer, which is used for recovery.
> >>
> >> If  CP_CRC_RECOVERY_FLAG is defined, then __set_ckpt_flags(ckpt, CP_CRC_RECOVERY_FLAG); is
> >> executed in each do_checkpoint actually, and CP will have that flag for each on-going-to-write node footer.
> >> I think the recovery process only needs to use the on-going-to-write node rather than the already-been-written
> >> node in the old image. The  already-been-written node in the old image should not appear in the node
> >> chain of recovery process, right?
> > Previously, we changed the disk layout of footer in node block, and then we
> > applied new verifying approach which has better reliability in order to avoid
> > chaining garbage node block.
> >
> > In order to distinguish old disk layout and the new one, we introduce
> > CP_CRC_RECOVERY_FLAG, once a CP is triggered, we will tag current CP with the
> > flag, and use new disk layout and new verifying approach for the following node
> > block updating flow and abnormal power-cut recovery flow.
> >
> > For old image which has no CP_CRC_RECOVERY_FLAG flag been set, f2fs needs to use
> > old disk layout and old verifying approach during recovery for the
> > compatibility. So that's why we need to check the flag in CP here.
> 
> For the old disk layout, because we still use new approach to set CP_CRC_RECOVERY_FLAG in the node footer in each do_checkpoint,
> then I think f2fs should also use new verifying approach during recovery rather than old verifying approach. What is the problem if
> we do like this?

This is to handle only one case in which:

1. uses old kernel without this flag,
2. calls fsync and gets sudden power-cut,
3. updates new kernel having this flag before mount.

Then, if we do not check this flag at mount time, we will lose the last fsync'ed
node blocks.

Thanks,

> 
> > Thanks,
> >
> >> On 2017/2/24 18:29, Chao Yu wrote:
> >>> On 2017/2/24 18:06, Yunlong Song wrote:
> >>>> No need to check the "if" condition each time, just change it to macro codes.
> >>> We're going to check flag in CP, not just in code of f2fs.
> >>>
> >>> Thanks,
> >>>
> >>>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
> >>>> ---
> >>>>  fs/f2fs/node.h    | 20 ++++++++++----------
> >>>>  fs/f2fs/segment.c |  5 +++--
> >>>>  2 files changed, 13 insertions(+), 12 deletions(-)
> >>>>
> >>>> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> >>>> index 3fc9c4b..3e5a58b 100644
> >>>> --- a/fs/f2fs/node.h
> >>>> +++ b/fs/f2fs/node.h
> >>>> @@ -303,11 +303,11 @@ static inline void fill_node_footer_blkaddr(struct page *page, block_t blkaddr)
> >>>>  	size_t crc_offset = le32_to_cpu(ckpt->checksum_offset);
> >>>>  	__u64 cp_ver = le64_to_cpu(ckpt->checkpoint_ver);
> >>>>  
> >>>> -	if (__is_set_ckpt_flags(ckpt, CP_CRC_RECOVERY_FLAG)) {
> >>>> -		__u64 crc = le32_to_cpu(*((__le32 *)
> >>>> -				((unsigned char *)ckpt + crc_offset)));
> >>>> -		cp_ver |= (crc << 32);
> >>>> -	}
> >>>> +#ifdef CP_CRC_RECOVERY_FLAG
> >>>> +	__u64 crc = le32_to_cpu(*((__le32 *)
> >>>> +			((unsigned char *)ckpt + crc_offset)));
> >>>> +	cp_ver |= (crc << 32);
> >>>> +#endif
> >>>>  	rn->footer.cp_ver = cpu_to_le64(cp_ver);
> >>>>  	rn->footer.next_blkaddr = cpu_to_le32(blkaddr);
> >>>>  }
> >>>> @@ -318,11 +318,11 @@ static inline bool is_recoverable_dnode(struct page *page)
> >>>>  	size_t crc_offset = le32_to_cpu(ckpt->checksum_offset);
> >>>>  	__u64 cp_ver = cur_cp_version(ckpt);
> >>>>  
> >>>> -	if (__is_set_ckpt_flags(ckpt, CP_CRC_RECOVERY_FLAG)) {
> >>>> -		__u64 crc = le32_to_cpu(*((__le32 *)
> >>>> -				((unsigned char *)ckpt + crc_offset)));
> >>>> -		cp_ver |= (crc << 32);
> >>>> -	}
> >>>> +#ifdef CP_CRC_RECOVERY_FLAG
> >>>> +	__u64 crc = le32_to_cpu(*((__le32 *)
> >>>> +			((unsigned char *)ckpt + crc_offset)));
> >>>> +	cp_ver |= (crc << 32);
> >>>> +#endif
> >>>>  	return cp_ver == cpver_of_node(page);
> >>>>  }
> >>>>  
> >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>> index 9eb6d89..6c2e1ee 100644
> >>>> --- a/fs/f2fs/segment.c
> >>>> +++ b/fs/f2fs/segment.c
> >>>> @@ -1573,9 +1573,10 @@ static void allocate_segment_by_default(struct f2fs_sb_info *sbi,
> >>>>  {
> >>>>  	if (force)
> >>>>  		new_curseg(sbi, type, true);
> >>>> -	else if (!is_set_ckpt_flags(sbi, CP_CRC_RECOVERY_FLAG) &&
> >>>> -					type == CURSEG_WARM_NODE)
> >>>> +#ifndef CP_CRC_RECOVERY_FLAG
> >>>> +	else if (type == CURSEG_WARM_NODE)
> >>>>  		new_curseg(sbi, type, false);
> >>>> +#endif
> >>>>  	else if (need_SSR(sbi) && get_ssr_segment(sbi, type))
> >>>>  		change_curseg(sbi, type, true);
> >>>>  	else
> >>>>
> >>> .
> >>>
> >>
> >
> > .
> >
> 
> 
> -- 
> Thanks,
> Yunlong Song
>