Re: [PATCH v4 2/3] ext4: record error when detect abnormal 'i_reserved_data_blocks'

[Theodore Ts'o]

On Thu, Dec 08, 2022 at 11:34:25AM +0800, Ye Bin wrote:
> From: Ye Bin <yebin10@xxxxxxxxxx>
> 
> If 'i_reserved_data_blocks' is not cleared which mean something wrong with
> code, free space accounting is likely wrong, according to Jan Kara's advice
> use ext4_error() to record this abnormal let fsck to repair and also we can
> capture this issue.

If i_reserved_data_block, it means that there is something wrong with
our delayed allocation accounting.  However, this accounting is
usually only an in-memory error.  The one exception is if quota is
enabled, in which case the space is decremented from the
user/group/project quota.

However, if quota is not in use, which is the overwhelmingly common
case, there will be nothing for fsck to repair.  (It does mean that df
will show a slightly smaller free space value due to the messed up
delayed allocation accounting, but that disappears after a reboot.)

Marking the file system as in need of repair when nothing is actually
wrong with the on-disk file system can backfire, in that it confuses
users when they see the ext4 error but then when they run fsck, fsck
reports nothing wrong --- at which point they file a bug.

We could use ext4_error if quotas are enabled, and ext4_msg if not,
but it might not worth the extra complexity.

Cheers,

					- Ted