Date:   Thu, 25 Mar 2021 09:59:43 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH] Revert "f2fs: give a warning only for readonly partition"

On 2021/3/25 6:44, Jaegeuk Kim wrote:
> On 03/24, Chao Yu wrote:
>> On 2021/3/24 12:22, Jaegeuk Kim wrote:
>>> On 03/24, Chao Yu wrote:
>>>> On 2021/3/24 2:39, Jaegeuk Kim wrote:
>>>>> On 03/23, Chao Yu wrote:
>>>>>> This reverts commit 938a184265d75ea474f1c6fe1da96a5196163789.
>>>>>>
>>>>>> Because that commit fails generic/050 testcase which expect failure
>>>>>> during mount a recoverable readonly partition.
>>>>>
>>>>> I think we need to change generic/050, since f2fs can recover this partition,
>>>>
>>>> Well, not sure we can change that testcase, since it restricts all generic
>>>> filesystems behavior. At least, ext4's behavior makes sense to me:
>>>>
>>>> 	journal_dev_ro = bdev_read_only(journal->j_dev);
>>>> 	really_read_only = bdev_read_only(sb->s_bdev) | journal_dev_ro;
>>>>
>>>> 	if (journal_dev_ro && !sb_rdonly(sb)) {
>>>> 		ext4_msg(sb, KERN_ERR,
>>>> 			 "journal device read-only, try mounting with '-o ro'");
>>>> 		err = -EROFS;
>>>> 		goto err_out;
>>>> 	}
>>>>
>>>> 	if (ext4_has_feature_journal_needs_recovery(sb)) {
>>>> 		if (sb_rdonly(sb)) {
>>>> 			ext4_msg(sb, KERN_INFO, "INFO: recovery "
>>>> 					"required on readonly filesystem");
>>>> 			if (really_read_only) {
>>>> 				ext4_msg(sb, KERN_ERR, "write access "
>>>> 					"unavailable, cannot proceed "
>>>> 					"(try mounting with noload)");
>>>> 				err = -EROFS;
>>>> 				goto err_out;
>>>> 			}
>>>> 			ext4_msg(sb, KERN_INFO, "write access will "
>>>> 			       "be enabled during recovery");
>>>> 		}
>>>> 	}
>>>>
>>>>> even though using it as readonly. And, valid checkpoint can allow for user to
>>>>> read all the data without problem.
>>>>
>>>>>>     		if (f2fs_hw_is_readonly(sbi)) {
>>>>
>>>> Since device is readonly now, all write to the device will fail, checkpoint can
>>>> not persist recovered data, after page cache is expired, user can see stale data.
>>>
>>> My point is, after mount with ro, there'll be no data write which preserves the
>>> current status. So, in the next time, we can recover fsync'ed data later, if
>>> user succeeds to mount as rw. Another point is, with the current checkpoint, we
>>> should not have any corrupted metadata. So, why not giving a chance to show what
>>> data remained to user? I think this can be doable only with CoW filesystems.
>>
>> I guess we're talking about the different things...
>>
>> Let me declare two different readonly status:
>>
>> 1. filesystem readonly: file system is mount with ro mount option, and
>> app from userspace can not modify any thing of filesystem, but filesystem
>> itself can modify data on device since device may be writable.
>>
>> 2. device readonly: device is set to readonly status via 'blockdev --setro'
>> command, and then filesystem should never issue any write IO to the device.
>>
>> So, what I mean is, *when device is readonly*, rather than f2fs mountpoint
>> is readonly (f2fs_hw_is_readonly() returns true as below code, instead of
>> f2fs_readonly() returns true), in this condition, we should not issue any
>> write IO to device anyway, because, AFAIK, write IO will fail due to
>> bio_check_ro() check.
> 
> In that case, mount(2) will try readonly, no?

Yes, if device is readonly, mount (2) can not mount/remount device to rw
mountpoint.

Thanks,

> 
> # blockdev --setro /dev/vdb
> # mount -t f2fs /dev/vdb /mnt/test/
> mount: /mnt/test: WARNING: source write-protected, mounted read-only.
> 
>>
>>   		if (f2fs_hw_is_readonly(sbi)) {
>> -			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>> -				err = -EROFS;
>> +			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG))
>>   				f2fs_err(sbi, "Need to recover fsync data, but write access unavailable");
>> -				goto free_meta;
>> -			}
>> -			f2fs_info(sbi, "write access unavailable, skipping recovery");
>> +			else
>> +				f2fs_info(sbi, "write access unavailable, skipping recovery");
>>   			goto reset_checkpoint;
>>   		}
>>
>> For the case of filesystem is readonly and device is writable, it's fine
>> to do recovery in order to let user to see fsynced data.
>>
>> Thanks,
>>
>>>
>>>>
>>>> Am I missing something?
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> Fixes: 938a184265d7 ("f2fs: give a warning only for readonly partition")
>>>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>>>> ---
>>>>>>     fs/f2fs/super.c | 8 +++++---
>>>>>>     1 file changed, 5 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>>>> index b48281642e98..2b78ee11f093 100644
>>>>>> --- a/fs/f2fs/super.c
>>>>>> +++ b/fs/f2fs/super.c
>>>>>> @@ -3952,10 +3952,12 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>>>>     		 * previous checkpoint was not done by clean system shutdown.
>>>>>>     		 */
>>>>>>     		if (f2fs_hw_is_readonly(sbi)) {
>>>>>> -			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG))
>>>>>> +			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>>>>>> +				err = -EROFS;
>>>>>>     				f2fs_err(sbi, "Need to recover fsync data, but write access unavailable");
>>>>>> -			else
>>>>>> -				f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>> +				goto free_meta;
>>>>>> +			}
>>>>>> +			f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>>     			goto reset_checkpoint;
>>>>>>     		}
>>>>>> -- 
>>>>>> 2.29.2
>>>>> .
>>>>>
>>> .
>>>
> .
> 

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