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Message-ID: <YFvA6uzDLeD7dRdY@google.com>
Date: Wed, 24 Mar 2021 15:44:58 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
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 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?
# 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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