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Message-ID: <c1e48546-f61b-5db9-13b6-6430ce368661@huawei.com>
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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