Date:   Fri, 26 Mar 2021 09:08:33 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] Revert "f2fs: give a warning only for readonly
 partition"

On 2021/3/25 9:59, Chao Yu wrote:
> 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.

Any other concern about this patch?

Thanks,

> 
> 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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